Author Topic: LED display for HP 3457A multimeter - I did it :-)  (Read 24808 times)

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Offline xi

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LED display for HP 3457A multimeter - I did it :-)
« on: November 10, 2017, 02:07:51 am »
    Hi there,

    The HP 3457A is a well known really good DMM, I bought one for my hobbyist lab (got two for some reasons). Its main drawback is the LCD display! It's hard to read, especially when doing some critical measurements on a board, and trying to read the DMM at the same time :-[

    I know there are some mods to add a backlight - though this is a good idea, I am not a big fan of LCD displays at all: there is always some angles where you don't see anything

    So I though it could be a good idea to rebuild a display with some LEDs :) There were two major difficulties:
    - reverse-engineer the HP LCD protocol.
    - recreate a display identical to the LCD one, eg with two point (colon) and a comma between each digit.

    I succeeded and here is the result (before / after):


I am going to show the different steps of the design.

  • HP LCD display protocol spying

I used 2 floppy drive disk ribbon cables to get a straight extension in order to connect my Saleae logic analyser. Then I tried to understand the HP LCD protocol (this was far from trivial, because the data for one digit are scattered at various places in the transmission frame).


But I succeeded and was able to decode the digits with an ATMega32:


  • Mechanical considerations
Second biggest problem was to add the two points and the comma between each digit. I initially though about using some really small LED 14 digit display and use some discrete LED between each digit, with eg some 3D printed light pipes. But there were two new problems with this solution: the smallest display I found are 10mm width (there are 12 digits, and the DMM window is about 120mm with - meaning that there is absolutely NO room for some LED between each digit). The other problem was the price of the 3D printed light-pipe: more than 60€!
So I thought about another solution: machine the displays to remove about 0.5mm on each side and use an additional PCB with some miniature LED in order to display the punctuation :-/O And it worked :) Below is the image of the aluminium support to machine 4 display at a time:


  • Electronic board
Next steps were to design the electronic board. I choose to design the display in 3 floors: one for the CPU and power / one for the 14 seg. displays / one for the punctuation. The board are single side PCB, so that I can easily engrave them at home. But I designed them with two layers, thus no straps are needed if they are engraved with two layers ;)
I used an Atmel ATMega162 which has 35 IO in a TQFP44 & DIP40 package (most of the other Atmel in this packages only have 32 IO lines). I will publish the schematics and some detailed explanations if there are some interests in that!
Below are the boards just drilled and cut on my CNC machine.


And here is the board just before engraving:


  • Assembly
The 3 boards after mounting all the components:



The hardest part was to solder the miniature LEDs, especially the comma, because normally these LEDs are designed to be mounted horizontally, but I mounted them vertically ... (I wasn't able to find any LED with an elongated form factor, except these ones).


Once assembled, comparison with the original LCD display:


The original HP ribbon cable is reused and inserted into a DIP support:

[/list]

To be continued...

Online Vgkid

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #1 on: November 10, 2017, 02:32:45 am »
That is really good looking , look forward to seeing more.
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Offline xi

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #2 on: November 10, 2017, 03:01:49 am »
follow-up

  • Tests
I used the SPI hardware module of the Atmel to retrieve the info from the HP 3457A. The frame are not SPI at all (10 bits vs 8 bits, ...), but adding a few discrete logic gates I was able to decode every frame of the HP DMM using the Atmel SPI.

First step was to display the decoded values in a serial terminal (Values in RED):


Then on the LED display - this is one of the first test I made:



All digit lit, once assembled:


  • Final result
I am really pleased with the final result: viewing angle are - as expected - really really good (see top and side views just below), and the display is really fast - data are displayed as soon as they are received ; I think it's even faster than the LCD version, because the CPU is faster. As for the refresh rate, I achieve 80Hz, so there is no visible flickering at all.

Power consumption is directly related to the brightness of the display. The yellow version of these Kingbright display would need about 10mA per segment to be really bright (meaning nearly 2A @ 5V for the 12x 14 segment display when everything is lit) ; this is way too high for the transformer of the DMM. I ended up in sending about 5mA per segment (mean value): when everything is lit, it adds about 4.5W of consumption on the transformer, and when some useful stuff is displayed, the consumption increase is about 2W, which is perfectly acceptable.
For the next module, I will choose red display, because there is a high luminosity version for this color.





That's all for now! If there are some interest, I will post the schematics and more detailed explanation ;)
« Last Edit: November 10, 2017, 03:06:29 am by xi »
 
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Offline IanB

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #3 on: November 10, 2017, 03:12:19 am »
Wow! That's some serious hacking. You must have been really upset with that LCD display  :)
I'm not an EE--what am I doing here?
 

Offline retiredcaps

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #4 on: November 10, 2017, 03:18:41 am »
Awesome job!  :-+

I have one bench meter, but I never use it.  It is a Keithley 175 and it has the same hard to read display at certain angles.  I got it for $30 CDN out of curiosity more than anything.

I can certainly say that I would never even attempt this LED modification given the time required to do so.  It is easier to reach for another handheld multimeter with a bigger display and backlight.
 

Offline ludzinc

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #5 on: November 10, 2017, 03:26:52 am »
WOW

A thing of beauty, and a Joy forever!
 

Offline drussell

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #6 on: November 10, 2017, 04:14:51 am »
Slick!   Nicely done!   :)
 

Offline rsjsouza

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #7 on: November 10, 2017, 04:20:58 am »
Congratulations on the modifications! The display looks stunning. I have two 3478As that have the same type of display... Perhaps some day I take the plunge to replace them...
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Offline Tomorokoshi

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #8 on: November 10, 2017, 04:24:39 am »
Very impressive. That would make a good upgrade kit.
 

Offline TheSteve

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #9 on: November 10, 2017, 05:21:52 am »
Hardcore - I love it!
VE7FM
 

Offline razberik

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #10 on: November 10, 2017, 09:24:20 am »
Amazing !
Shall it fit to 3478A ?
 

Offline kripton2035

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #11 on: November 10, 2017, 09:40:08 am »
you can start a kickstarter for this now ... ;)
 

Offline brabus

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #12 on: November 10, 2017, 10:08:43 am »
Very, very well made. Congratulations!
 

Offline tooki

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #13 on: November 10, 2017, 11:56:00 am »
Wow, that's beautiful!!!

I've never used that model or any relative. What does it use the colons between digits for?
 

Offline tooki

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #14 on: November 10, 2017, 12:01:32 pm »
Awesome job!  :-+

I have one bench meter, but I never use it.  It is a Keithley 175 and it has the same hard to read display at certain angles.  I got it for $30 CDN out of curiosity more than anything.
I'm working with Technogeeky to come up with a replacement display board for the Keithley 197/197A, and I wouldn't be surprised if it used a very similar display board, if not the same one. Keep your eyes peeled. :)
 

Offline Mr. Scram

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #15 on: November 10, 2017, 12:04:58 pm »
Nice job, and certainly something I would have been interested in if I didn't lose the auction the other day.
 

Offline capt bullshot

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #16 on: November 10, 2017, 12:06:25 pm »
Wow, that's stunning
Great job!
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Offline ElektroQuark

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #17 on: November 10, 2017, 12:30:03 pm »
 :clap:

Impressive work.
As someone has noted, you could sell some kits.

Offline Dr. Frank

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #18 on: November 10, 2017, 01:12:50 pm »
Great job, very well done and documented!
Thanks for sharing.
 

Online xrunner

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #19 on: November 10, 2017, 01:17:11 pm »
Impressive - most impressive!  :clap:
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Offline Back2Volts

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #20 on: November 10, 2017, 03:20:12 pm »
Wow, awesome, impressive, most impressive...   what else can I say !!!
 

Offline sokoloff

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #21 on: November 10, 2017, 03:25:53 pm »
Hacks like this are simply amazing to me.
Such dedication and effort for such an elegant outcome; I love it.

I'd love to see the schematics and more detailed information about how did the decoding and reverse engineering. (It's not like I even own that equipment, but I love reading the nitty-gritty details.)
 

Offline bookaboo

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #22 on: November 10, 2017, 03:58:06 pm »
Incredible job  :-+ :-+
 

Offline ealex

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #23 on: November 10, 2017, 04:16:30 pm »
that's awesome  :-+

i'm interested in the protocol .
maybe a small CPLD can be used to capture the data an drive the display ?
 

Offline cvanc

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #24 on: November 10, 2017, 04:44:15 pm »
Beautiful, elegant work.  Well done.
 

Offline bingo600

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #25 on: November 10, 2017, 05:39:20 pm »
Wooowww   :clap: :clap:

Very nice looking mod  :-+

Any chance you would describe the protocol ?

/Bingo
 

Offline stj

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #26 on: November 10, 2017, 06:17:16 pm »
that's an incredible amount of mechanical effort!!

i would have used a starburst VFD, it would have looked good, but probably not even close to that good.  :-+
 

Offline texaspyro

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #27 on: November 10, 2017, 07:48:35 pm »
I've got 3 or 4 3457's hanging around here that could use a display upgrade.  If you build more of these, I'm in.  I'd also be interested in your code / protocol info.   I'd probably implement it using a VFD or modern backlight LCD.

I have a project on the back burner to do a replacement front panel board for the HP-531xx counters using (probably) a backlit LCD.  There are a lot of those out there with weak VFD's.  HP only sells the display as a complete front panel board... $1800.
 

Offline xi

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #28 on: November 11, 2017, 12:42:15 am »
Wow, I didn't expect so many answers! Thanks for your nice comments about my mod :D

Just answering quickly some of your questions ; I will post the protocol and schematic on tomorrow, I am too tired tonight ;)

As for the 3478A, I think it would work too (I used the doc of this DMM to get the pinout of the display and the function of each line - it is more detailed than the 3457A one). But, you would loose the indications at the bottom of the display (MATH, CAL, SHIFT, ...), because on the 3478A, these indications appear directly on the display (contrarily to the 3457A where the indications are printed below the display).

The colon is used to describe parameter's value. For example, if you launch the command "ID?" from the menu, it displays "ID?:HP3457A".

As for selling a kit ... I don't know, I think it would be too expensive compared to the current price of the HP 3457A. But I will calculate with the BOM.

 

Offline Macbeth

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #29 on: November 11, 2017, 01:31:29 am »
Amazing job, especially all that work to add the colons and commas on the third PCB.  :-+

Please do publish the protocol, even though it removes some of the fun for us masochists who enjoy reverse engineering that kind of stuff!
 

Offline Dave

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #30 on: November 11, 2017, 04:12:02 am »
Absolutely superb! These are the kinds of amazing projects that keep me hooked to this forum. :-+
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Offline timb

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #31 on: November 11, 2017, 04:50:07 am »
Awesome job!  :-+

I have one bench meter, but I never use it.  It is a Keithley 175 and it has the same hard to read display at certain angles.  I got it for $30 CDN out of curiosity more than anything.
I'm working with Technogeeky to come up with a replacement display board for the Keithley 197/197A, and I wouldn't be surprised if it used a very similar display board, if not the same one. Keep your eyes peeled. :)

We should pool our resources, as I’m halfway done with an OLED mod for the 197. I’ve almost got the mechanical portion down (I designed a small frame that can be laser cut from plastic), now all I need to do is design the replacement PCB. The trick is getting the button positions right (I’ve scanned in the existing board so I can get precise measurements).

I’ve also got some preliminary firmware going on an MSP430 to decode the signals.

I’m still waiting on the OLEDs to get in from China so I can try it out on the meter itself.

Initially, I was going to use LEDs like the OP’s 3457A mod, however it would have been difficult to replicate the annunciator symbols (BATT, HOLD, etc.) without implementing a diffuser and custom cut mask (I experimented with cutting the symbols into a black vinyl mask, adding a diffuser and then lighting them from behind with a single LED, but I wasn’t quite satisfied with the results). An LED cluster would have also used a lot power, which the 197 doesn’t have to spare. An OLED display won’t use more than 50mA, which is inside the 5VD rail’s buffer.

Anyway, send me a PM, I’m about 50% done with my project. I was planning on releasing it as a retrofit kit.



As for the OP’s project: A work of art! Please release schematics and such. From the looks of the 3457A’s LCD and interface, this LED mod should be extendable to other gear from that era, like the HP 3488A switch mainframe, which has the same style LCD as the 3457A. (In fact, it may even be the same LCD, it’s the same size and alphanumeric, with bottom markers and everything.)
Any sufficiently advanced technology is indistinguishable from magic; e.g., Cheez Whiz, Hot Dogs and RF.
 
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Offline precaud

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #32 on: November 11, 2017, 06:53:03 am »
Superb! Congrats!  I want one!
 

Offline TiN

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #33 on: November 11, 2017, 07:10:47 am »
Very cool, impressed with amount of work into that old meter.  :-+
Where did you get black screen in front of LEDs for contrast? I'm looking for that film for VFD displays...
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Offline cs.dk

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #34 on: November 11, 2017, 08:21:45 am »
Very nice mod :-+ :-+
 

Offline SeanB

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #35 on: November 11, 2017, 08:31:49 am »
Looks like a regular 80% or so solar film, simply cut to size. You can buy a whole roll, or just ask any car tint installer for an offcut in the desired shade and they likely will have a load of pieces you can cut the window out of for free.
 

Offline tggzzz

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #36 on: November 11, 2017, 08:43:41 am »
Have you done any tests to ensure and assure that changes in the current powering the LEDs doesn't affect the measurements?
« Last Edit: November 11, 2017, 08:45:50 am by tggzzz »
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline hugo

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #37 on: November 11, 2017, 07:50:06 pm »
Congrats to you XI, awesome job.  ;)
 

Offline cncjerry

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #38 on: November 11, 2017, 08:25:28 pm »
I'm really impressed.  I have two of those meters and coupled with very bad eyesight with Glaucoma and cataracts, I hate the display.  Absolutely hate it.

Did you engrave the boards with CNC or etch them?

Nice work all around.

Jerry
 

Offline xi

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #39 on: November 11, 2017, 11:52:40 pm »
HP 3457A multimeter LCD display protocol

As several of you asked for it, this is the protocol of the HP LCD display :-DMM

  • Electrical lines description
A 34 pin HE10 connector is used on the HP 3457A digital motherboard (same as those used for the 3.5" floppy drives). The ribbon cable attached is cut in two parts: pins 1 to 16 for the keyboard and pins 17 to 32 for the LCD display (pins 33 and 34 are NC).

Below is the pinout and the description of the LCD part of this HE10 connector.
Code: [Select]
                                               (NC) 17|18 (V3V: power supply for the LCD)
                            (instruction line: ISA) 19|20 (V2V: power supply for the LCD)
(1 = read data on ISA / 0 = read data on INA: SYNC) 21|22 (V1V: power supply for the LCD)
                                               (NC) 23|24 (GND)
                                   (data line: INA) 25|26 (OS1: for internal oscillator of the LCD display ; connected to a 470pF capacitor on the motherboard)
  (second clock, same as O1 with a small delay: 02) 27|28 (NC)
                                        (clock: 01) 29|30 (NC)
                          (global chip select: PWO) 31|32 (VCC: +5V with a serial resistor of 1k on the motherboard)
                                               (NC) 33|34 (NC)

So this is a serial synchronous transmission, and for us there are 5 interesting lines: PWO, 02 clk, SYNC, ISA and INA. With these lines we are able to completely decode the protocol of the LCD display. (note: O1 and O2 clocks are exactly the same, but the O2 line is 6µs late compared to O1. We will use rising edge of O2 clock to sample the data, because it has the best timing (middle of each data bit)).

Note: the pinout of the DIL connector (LCD end of the ribbon cable) is given on my schematic that I will publish soon. Basically, pin 17 of the HE10 goes to pin 1 of the DIL support, pin 18 on pin 2, ... and pin 32 on pin 16!


  • Protocol overview


Let's observe a capture of a full frame (once received, this frame will display the above text "BEEP,-99999.1_", with two annunciators lit : "SMPL" & "MATH"):


Description of each line:
PWO: this is the global chip select, when at level "1", the LCD display is selected and must read the data.
CLK 02: this is the clock for the data received on ISA and INA lines. Max clock frequency is 55kHz (may be less, I guess it depends on the processor load).
SYNC: this line is at level "1" when the data must be read on ISA line / at level "0" when the data must be read on INA line. On the above screenshot, the SYNC line goes "high" 7 times, meaning there are 7 instructions sent on ISA line
ISA: this line sends the instructions to the LCD display, I have found 7 types of instructions:
 - 0x3F0: select the LCD display (1 byte)
 - 0x2E0: ?
 - 0x320: toggle display ON/OFF
 - 0x2F0: annunciators ON/OFF ("SMPL", "REM", "SRQ", "ADRS", "AC+DC", "4W", "AZOFF", "MRNG", "MATH", "REAR", "ERR", "SHIFT") (2 bytes)
 - 0x028: write A registers (6 bytes)
 - 0x068: write B registers (6 bytes)
 - 0x0A8: write C registers (6 bytes)
INA: this line sends the data to the LCD display (eg the values to display on the digits)

Chip Select: is not a line from the motherboard, it is generated by my board with a bit of logic (we will see why later)

Let's zoom on the complete frame: complete frame (very large image)
We can see 7 instructions sent on the ISA line in this order: 0x3F0, 0x2E0, 0x320, 0x2F0, 0x0A8, 0x028, 0x068. Some frame will have less instructions, in fact, only the data that change are re-transmitted (if you press the "SINGLE" button of the DMM, the data are sent once to the LCD display, then nothing changes, so nothing is transmitted anymore (to be exact, when nothing changes, the data are retransmitted each 2 minutes or so).
Below is a screenshot of two successive frames, one has 7 instructions, the following only has 4 instructions, because only the annunciator changed:


The INA line shows the data that follow each instruction. In the following section we will describe the useful sections more in-depth.


  • Examining the first instruction: 0x3F0 = select the display
General info about the transmission:
- Each bit are transmitted reverse, ie the bit 0 (= Least Significant Bit) of a register is sent first ...
- The same apply for the digits: digit 12 (the last one) is transmitted first ...

Let's observe the first instruction received on the above complete frame: 0x3F0:

The doc I found says this instruction is to select the display, and the display is selected when the data received on INA line is 0xFD. Let's verify!

Let's check the instruction between C1 and C2 markers first: remember that instructions are sent on ISA line when SYNC line is at level "1". On the above screenshot, we can see that we received these bits:
0000111111 (10 bits).
Also remember that the bits are sent in reverse order, so once reordered, the data on ISA line is:
1111110000 = 0x3F0 = select the LCD display command :-+

Now we are going to check the data between A1 and A2 markers: remember that data are sent on INA line when SYNC line is at level "0". On the above screenshot, we can see that we received these bits:
10111111 (8 bits).
Also remember that the bits are sent in reverse order, so once reordered, the data on INA line is:
11111101 = 0xFD = select the LCD display value :-+

What about the bits received between C2 and A1 markers ? (two clock pulses)
There are always these two bits, whatever the line (ISA or INA), and they are always 0. The useful data always starts after these 2 bits, and are then sent on a multiple of 8 bits.
In other words, each transmission of data starts with a 10 bits set, followed by n 8 bits sets. But since the first 2 bits are always 0, we can ignore them and consider that the data are only composed of 8 bits sets.
Ignoring these 2 bits is not an easy task for the microcontroller, because it is not designed to receive a variable length of data on the SPI bus ;) For this reason, I have added a bit of logic (two D flip-flop to delay the SYNC signal and an XOR gate to generate my "Chip Select"). With this logic, I am able to decode directly the data from the HP 3457A using the hardware SPI module from the Atmel microcontroller (the "Chip Select" line directly drives the CS input of the Atmel: the CS input is only enabled when at logic level "0" :)).


  • The Digits part
Ok, I hope you have understood how the frame is built, so now let's decode the interesting part of the frame: the data sent to the digits 8)
We will ignore the useless (for the mod) instructions (0x2F0, ...) and we will decode the 0x028 / 0x068 / 0x0A8 instructions. There are 3 registers of 6 bytes each = 18 bytes in total to describe the 12 chars of the display + the punctuation. Each register is set by one instruction received on ISA line: 0x028 for register A, 0x068 for register B and 0x0A8 for register C.

This screenshot shows the complete decoding of the 0x028 command (values for register A), up to the next command 0x068.

The principle for decoding this instruction is exactly the same as for the "First instruction: 0x3F0", so refer to this section to understand it ;)
The data set received for register A is (hexadecimal): 1F 99 99 D9 50 25

Note that there are 6 more bytes transmitted after these 6 bytes, but they are always 0, so we don't bother to retrieve and decode them (I don't know the purpose of these bytes).

This is screenshot for 0x068 command = values for register B:

The exact same principle applies to decode it, and the data set received is: 31 37 33 23 0D 00

Similarly, the register C (0xA8 command) will decode as: 00 00 00 00 00 00

Ok, so "BEEP,-99999.1_" is displayed on the screen, and we have 3 registers, containing the following values ... how to match them?
 reg A = 1F 99 99 D9 50 25
 reg B = 31 37 33 23 0D 00
 reg C = 00 00 00 00 00 00


  • Decode the Digits
After much research for "HP LCD charset" and other similar things, I ended-up finding this little treasure: the complete doc of a ROM for the HP41C! This is a calculator that contains a LCD display with a similar protocol as the one used on the DMM ; thanks HP for the good consistency between the products :-+ This is here: http://www.series80.org/Misc/ZenROM.pdf

The most interesting info are on page 115 and following (section 8.2 "Display handling"):
- description of the format of the frames
- description of the instructions (some are missing, like the 0x2E0, but it's enough to understand the protocol)
- and the most interesting: the HP character set for the LCD display! 8) Below is a reproduction of this charset, with the value for each char (eg, char 'X' has value "0x18")


Each byte of register A contains 4 LSB bits for each digit (meaning there are the LSB part of 2 digits in each byte)
Similarly, each byte of register B contains 2 MSB bits for 2 digits and 2 bits for the punctuation of 2 digits
And, each byte of register C contains the Extended bit for 2 digits.

Below is a table that represents the 6 bytes received for each registers (A, B & C), and the matching digits data.
Code: [Select]
----------------------------------------------------------------------------------------------------------------------
|Byte nr received |        1        |        2       |       3       |       4       |       5       |       6       |
----------------------------------------------------------------------------------------------------------------------
|Digit number     |   11   |   12   |   9   |   10   |   7   |   8   |   5   |   6   |   3   |   4   |   1   |   2   |
----------------------------------------------------------------------------------------------------------------------

Char value is given by retrieving the following bits from register A, B & C:
(The first line represents the 7 bits of the char value ; this value directly matches the HP charset showed above)
(The second and third line show which register and bit needs to be read to retrieve the char value. Eg, "RegB3_bit1" means Register B, byte 3, bit 1)
Code: [Select]
------------------------------------------------------------------------------------------------------------------------------
| bit number for one char         |     6      |     5      |     4      |     3      |     2      |     1      |     0      |
------------------------------------------------------------------------------------------------------------------------------
| pos in the reg. for even digits | RegCn_bit0 | RegBn_bit1 | RegBn_bit0 | RegAn_bit3 | RegAn_bit2 | RegAn_bit1 | RegAn_bit0 |
------------------------------------------------------------------------------------------------------------------------------
| pos in the reg. for odd digits  | RegCn_bit4 | RegBn_bit5 | RegBn_bit4 | RegAn_bit7 | RegAn_bit6 | RegAn_bit5 | RegAn_bit4 |
------------------------------------------------------------------------------------------------------------------------------

Lets apply this table to our example. Remember we got these values in the registers:
 reg A = 1F 99 99 D9 50 25
 reg B = 31 37 33 23 0D 00
 reg C = 00 00 00 00 00 00

So if we want to decode digit 4 for example, using the first table, we know that digit 4 data are stored in byte number 5:
Digit 4 data are 50 (reg A), 0D (reg B), 00 (reg C). Written in binary, this is:
01010000 (reg A), 00001101 (reg B), 00000000 (reg C)
Now we use the second table to decode the char ; digit 4 is an even number, so decoding is done using these bits:
Code: [Select]
| RegC_bit0 | RegB_bit1 | RegB_bit0 | RegA_bit3 | RegA_bit2 | RegA_bit1 | RegA_bit0 |
|     0     |     0     |     1     |     0     |     0     |     0     |     0     |
= 0010000 = 0x10
Last, we use the HP charset to see that char 0x10 is the letter 'P', eg what was expected ;D (forth digit of "BEEP,-99999.1_" text)


  • Decode the Punctuation
The punctuation is transmitted in the register B, using the exact same principle as above.
Code: [Select]
-------------------------------------------------------------
| bit number for the punctuation  |     1      |     0      |
-------------------------------------------------------------
| pos in the reg. for even digits | RegBn_bit3 | RegBn_bit2 |
-------------------------------------------------------------
| pos in the reg. for odd digits  | RegBn_bit7 | RegBn_bit6 |
-------------------------------------------------------------

And the charset for the punctuation is this one:
Code: [Select]
--------------------
|Value | Sign      |
--------------------
| 0    |   (none)  |
| 1    | . (point) |
| 2    | : (colon) |
| 3    | , (comma) |
--------------------
(note: the annunciators are transmitted separately in another instruction)

Lets apply this table to our example. Remember we got these values in the registers:
 reg A = 1F 99 99 D9 50 25
 reg B = 31 37 33 23 0D 00
 reg C = 00 00 00 00 00 00

So if we want to decode punctuation for digit 10 for example, using the first table, we know that digit 10 data are stored in byte number 2:
So, digit 10 data is 0x37 (reg B) = 00110111 (reg B)
Now we use the punctuation decoding table ; digit 10 is an even number, so decoding is done using these bits:
Code: [Select]
| RegB_bit3 | RegB_bit2 |
|     0     |     1     |
= 0b01 = 1
Last, we use the charset for the punctuation to see that value 1 corresponds to punctuation '.' (point), eg what we expected ;D (punctuation for 10th digit of "BEEP,-99999.1_" text)


  • Decode the Annunciators
Remember, the annunciators are the functions "SMPL", "REM", "SRQ", "ADRS", "AC+DC", "4W", "AZOFF", "MRNG", "MATH", "REAR", "ERR", "SHIFT" below the display.
They are send just after the instruction 0x2F0, like in the screenshot below:


As always, the instruction is between C1 & C2 markers. Decoding the instruction gives 0x2F0, which indicates that the annunciators will follow on INA line.

Decoding the annunciator is really simple: they are sent on INA line between markers D1 & D2, and there is one bit per annunciator. The only difficulty is that they are written reverse (as always), so the first transmitted bit is the last annunciator.
Code: [Select]
---------------------------------------------------------------------------------------------------
| annunciator  | SMPL | REM | SRQ | ADRS | AC+DC | 4Wo | AZOFF | MRNG | MATH | REAR | ERR | SHIFT |
---------------------------------------------------------------------------------------------------
| bit position |  12  | 11  | 10  |  9   |   8   |  7  |   6   |  5   |  4   |  3   |  2  |   1   |
---------------------------------------------------------------------------------------------------

Applied to our example, we have bit's positions 4 and 12 which are at level "1", meaning that "MATH" indicator and "SMPL" indicators are ON ;)


  • Literature
- This is the key documentation, starting at page 115, it gives the instructions supported by the display, and the complete charset: http://www.series80.org/Misc/ZenROM.pdf
- This one shows the representation of the HP charset on 14 segments display (the chars are scattered at various places, and some symbols are missing) : https://www.pungerer.net/pfx/MesPockets/HP/hp41cv/QuickCards/HP41QuickGuideSunthProgA.jpg
- The service manual of the HP 3478A for the description of the LCD display lines (page 141, section 7-F-66): http://www.arimi.it/wp-content/Strumenti/HP/Multimetri/hp-3478a-Service.pdf


That's the end! I have spent a lot of time writing this "spec" ; I hope it will benefit to someone!
Feel free to ask if something is unclear or poorly written ...
« Last Edit: November 12, 2017, 12:07:53 am by xi »
 

Offline xi

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #40 on: November 12, 2017, 01:38:14 am »
Very cool, impressed with amount of work into that old meter.  :-+
Where did you get black screen in front of LEDs for contrast? I'm looking for that film for VFD displays...
This is grey perspex (the original brand) ref 923 in 3mm thickness. I have tested several colors, and this one is the best for this application (once multimeter is closed, you don't see at all the unlit digits nor the punctuation). Specs are here: http://www.perspexsheet.uk/neutral-923-perspex/ and I bought it from here: https://www.ebay.fr/itm/361076230021

And no problem at all to machine this perspex sheet on my CNC:



Have you done any tests to ensure and assure that changes in the current powering the LEDs doesn't affect the measurements?
The original HP 3457A consumes about 9.5W on the mains input line, with the extension board inserted. The mains fuse is 80mA at 230V, meaning that max power consumption could be 18W in theory (just to give an idea). The LED module consumes 2W in normal use with yellow displays (up to 4.5W when all digits are lit). It is plugged directly on the same transformer output as the digital motherboard, using an extension (see image below), so I don't load at all the 5V regulator of this board nor I load the windings used for the analog board.

I have also measured the input voltage on the 5V regulator of the digital board: 10.9V when the LED display is disconnected / 10.4V when the LED display is connected and used normally / 10V when the LED display is all lit. And ripple is 0.5V peak-peak on this input, so the 5V regulator will fully work at all loads.

So I am quite confident that the power consumption increase will not affect at all the measurements. HP took a large security margin for the voltages, and after several hours of work, the transformer keeps quite cool.
In case of doubt, I could still mount the red version of the Displays, which is low power / high brightness, and thus reduce the power consumption by a factor 2 I think.




I'm really impressed.  I have two of those meters and coupled with very bad eyesight with Glaucoma and cataracts, I hate the display.  Absolutely hate it.

Did you engrave the boards with CNC or etch them?

Nice work all around.

Jerry
Thanks for your feedback!
And sorry, I used the wrong term: the boards are etched and not engraved, you are right ;) I use the CNC to drill and cut them.
« Last Edit: November 12, 2017, 01:44:48 am by xi »
 
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Offline tggzzz

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #41 on: November 12, 2017, 08:18:32 am »
Have you done any tests to ensure and assure that changes in the current powering the LEDs doesn't affect the measurements?
The original HP 3457A consumes about 9.5W on the mains input line, with the extension board inserted. The mains fuse is 80mA at 230V, meaning that max power consumption could be 18W in theory (just to give an idea). The LED module consumes 2W in normal use with yellow displays (up to 4.5W when all digits are lit). It is plugged directly on the same transformer output as the digital motherboard, using an extension (see image below), so I don't load at all the 5V regulator of this board nor I load the windings used for the analog board.

I have also measured the input voltage on the 5V regulator of the digital board: 10.9V when the LED display is disconnected / 10.4V when the LED display is connected and used normally / 10V when the LED display is all lit. And ripple is 0.5V peak-peak on this input, so the 5V regulator will fully work at all loads.

So I am quite confident that the power consumption increase will not affect at all the measurements. HP took a large security margin for the voltages, and after several hours of work, the transformer keeps quite cool.
In case of doubt, I could still mount the red version of the Displays, which is low power / high brightness, and thus reduce the power consumption by a factor 2 I think.

You missed a key word in my question, even though I used italics to emphasise it: changes.

Your response above is about the mean power dissipation. Your calculations and measurements may well be true, but are only vaguely relevant and are not definitive.

The LCD display will draw a constant current no matter what is displayed. The LED display will draw a different current depending on what is displayed. Every time the current changes there might well be some noise injected into the instrument's sensitive front-end - and that could affect the measurement.

If the display is multiplexed, and most LED displays are multiplexed to reduce the pin/wire count, then the current will change at the digit rate. The worst noise injection would probably occur when the display is 181818 or 111888 since  5 segments are changing from on to off and vice versa.

If, unusually, the display is not multiplexed, then the worst noise injection would occur whenever the displayed value changes. If no part of the measurement cycle is occurring at that time, then noise injection would probably be unimportant.

Without having considered the problem in detail, I will guess that any problems are most likely to appear with measurements:
  • high source impedance, say 100kohms to pick a common value in metrology
  • AC, not DC (although there might also be issues with DC measurements)
  • values near 0V
  • where a sub-harmonic of the multiplexing is near the mains line frequency, so that the mains frequency filter does not remove interference from the main
  • where the number of displayed segments changes most, e.g. 181818
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline voltsandjolts

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #42 on: November 12, 2017, 09:42:47 am »

Quote
That's the end! I have spent a lot of time writing this "spec"

Well done on the reverse engineering and the nice write-up, much appreciated  :-+
 

Offline xi

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #43 on: November 12, 2017, 09:15:56 pm »
Have you done any tests to ensure and assure that changes in the current powering the LEDs doesn't affect the measurements?
[...]
So I am quite confident that the power consumption increase will not affect at all the measurements. HP took a large security margin for the voltages, and after several hours of work, the transformer keeps quite cool.
In case of doubt, I could still mount the red version of the Displays, which is low power / high brightness, and thus reduce the power consumption by a factor 2 I think.

You missed a key word in my question, even though I used italics to emphasise it: changes.

Your response above is about the mean power dissipation. Your calculations and measurements may well be true, but are only vaguely relevant and are not definitive.
No, I didn't miss the word in your question ;) Simply, as you must have noticed, English is not my native language and I have understood your sentence differently: I though you were talking about "changes in the current powering the LEDs" compared to the current powering the LCD, and I have answered to that question. In fact you were talking about current variations during the LEDs commutation. Sorry, It must be perfectly clear for the natives, but it was unclear for me.

The display is obviously multiplexed, otherwise It would need more than 200 pins to drive the LEDs and 200 wire passing from one board to the other in my design! Yes, the worst case is when I switch from one digit with many segments lit to a digit completely OFF (like when there is a space in the text displayed).

When designing the power supply, the perturbations were one of my concern: I have added some external filtering (coil and capacitors) at the input of the Murata DC/DC converter, in order to reduce EMI (there are some spectral analysis given by Murata that guarantee the max value of the EMI when using these external components).

I guess your overall question is about EMI? Conducted EMI or radiated EMI?
As for the conducted EMI, I am not too worried: the LED commutation is low frequency and this is typically well filtered by the capacitors and the regulators of the DMM. Moreover, a power filter doesn't eliminate these low frequencies either, so they do cross the transformer, as well as my board may generate them, and the DMM is designed to work with that.
I was a bit more worried about the higher frequency EMI (included those generated by the DC-DC), hence the coil, and hence my connection on the "Digital" winding of the transformer and not the "analog" one (I don't know if it is useful, but it won't hurt, moreover than HF generally doesn't cross well a 50Hz power transformer).
And I was also worried about radiated EMI, and for this part, I have no real clues, nor any device to measure them.

As for your proposed "problematic" tests:
- I did some measurements near 0 with a µV DC source (see the firsts photos), and results are really good: there is absolutely no visible change between the LCD version and the LED version.
- Today I did some tests with a resistor, as you advised: mounted the LCD display back, used a high stability 200k resistor, waited 3 hours for the equipment and the resistor to be perfectly warmed, mounted back the LED display, waited a bit more and compared the results: at the same room temperature (22.5°C), the result are exactly the same: 200.0118kOhms.
- I don't have a stable enough AC source, so I can't answer you on this part.
- I did another test too: simply choosing the "FREQ" measurement with nothing connected to the inputs: it still displays 50Hz as it did before, so I guess there are not too much radiated EMI.

The comparison tests I did don't show any problem, but no, I just can't assure that the LED display doesn't affect measurements. I just did what I though good to maximise my chances of success, and it seems to be OK when comparing before/after, but assuring that would need costly measurement equipments that I don't have.

Hope this answers part of your question. If you think there are some designs flaw, or if you know better ways of designing LED display, please say so. I have some Enertec 7045 here too with the schematics, I will take a look at their design.

P.S. I will be without internet during 1 week, so don't expect too quick answer.
 

Offline tggzzz

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #44 on: November 13, 2017, 12:33:35 am »
Have you done any tests to ensure and assure that changes in the current powering the LEDs doesn't affect the measurements?
[...]
So I am quite confident that the power consumption increase will not affect at all the measurements. HP took a large security margin for the voltages, and after several hours of work, the transformer keeps quite cool.
In case of doubt, I could still mount the red version of the Displays, which is low power / high brightness, and thus reduce the power consumption by a factor 2 I think.

You missed a key word in my question, even though I used italics to emphasise it: changes.

Your response above is about the mean power dissipation. Your calculations and measurements may well be true, but are only vaguely relevant and are not definitive.
No, I didn't miss the word in your question ;) Simply, as you must have noticed, English is not my native language and I have understood your sentence differently: I though you were talking about "changes in the current powering the LEDs" compared to the current powering the LCD, and I have answered to that question. In fact you were talking about current variations during the LEDs commutation. Sorry, It must be perfectly clear for the natives, but it was unclear for me.

Those are reasonable points. My apologies for being unnecessarily belligerent.

Quote
The display is obviously multiplexed, otherwise It would need more than 200 pins to drive the LEDs and 200 wire passing from one board to the other in my design! Yes, the worst case is when I switch from one digit with many segments lit to a digit completely OFF (like when there is a space in the text displayed).

When designing the power supply, the perturbations were one of my concern: I have added some external filtering (coil and capacitors) at the input of the Murata DC/DC converter, in order to reduce EMI (there are some spectral analysis given by Murata that guarantee the max value of the EMI when using these external components).

I guess your overall question is about EMI? Conducted EMI or radiated EMI?

Either or both :) From a users perspective it wouldn't matter since either would be bad.

Quote
As for the conducted EMI, I am not too worried: the LED commutation is low frequency and this is typically well filtered by the capacitors and the regulators of the DMM. Moreover, a power filter doesn't eliminate these low frequencies either, so they do cross the transformer, as well as my board may generate them, and the DMM is designed to work with that.
I was a bit more worried about the higher frequency EMI (included those generated by the DC-DC), hence the coil, and hence my connection on the "Digital" winding of the transformer and not the "analog" one (I don't know if it is useful, but it won't hurt, moreover than HF generally doesn't cross well a 50Hz power transformer).
And I was also worried about radiated EMI, and for this part, I have no real clues, nor any device to measure them.

Any such measurement is difficult - and unreliable in the sense that it is difficult to reproduce and easy to measure a different value.

Quote
As for your proposed "problematic" tests:
- I did some measurements near 0 with a µV DC source (see the firsts photos), and results are really good: there is absolutely no visible change between the LCD version and the LED version.
- Today I did some tests with a resistor, as you advised: mounted the LCD display back, used a high stability 200k resistor, waited 3 hours for the equipment and the resistor to be perfectly warmed, mounted back the LED display, waited a bit more and compared the results: at the same room temperature (22.5°C), the result are exactly the same: 200.0118kOhms.

Did you try measuring the DC voltage across the (relatively high) resistor, which should, of course, be zero. The AC voltage across the resistor should be the thermal Johnson noise in the resistor. If not then it is possible that interference is causing problems - of which one interference source might be from the LED commutation currents.

Quote
- I don't have a stable enough AC source, so I can't answer you on this part.
- I did another test too: simply choosing the "FREQ" measurement with nothing connected to the inputs: it still displays 50Hz as it did before, so I guess there are not too much radiated EMI.

I think it would be unlikely that the meter could measure a frequency of switching noise.

Quote
The comparison tests I did don't show any problem, but no, I just can't assure that the LED display doesn't affect measurements. I just did what I though good to maximise my chances of success, and it seems to be OK when comparing before/after, but assuring that would need costly measurement equipments that I don't have.

Accepted, but if you lack expensive equipment then you have to think and to use skill and imagination - which is usually beneficial :)

Quote
Hope this answers part of your question. If you think there are some designs flaw, or if you know better ways of designing LED display, please say so. I have some Enertec 7045 here too with the schematics, I will take a look at their design.

P.S. I will be without internet during 1 week, so don't expect too quick answer.

No answer is necessary!

If you can devise measurements that would be most affected by interference, and can compare the measurements with an unmodified meter, and show there is no difference, then you have gone a long way to demonstrating interference isn't a problem.
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline coromonadalix

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #45 on: November 15, 2017, 09:47:47 pm »
wow   just wow    i wish i could do some reverse protocol etc ... ,  great work
 

Online Specmaster

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #46 on: November 16, 2017, 12:24:10 am »
Really is a great job you did there and I agree with the other lads on here, you could set up a small manufacturing process for these and sell them as complete replacement displays.

Perhaps starting up a small company designing replacement displays for other similar meters now you know how to do it. This could be your chance to go into business developing these kits and offering them as kits and or complete pre-built units with all the instructions on the procedure for fitting the replacement displays?  :-+ :-DMM
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Offline Keicar

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #47 on: November 16, 2017, 01:16:29 am »
I'm in awe - that's gorgeous!

Cheers,

Karl.
 

Offline Echo88

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Offline Swake

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #49 on: November 16, 2017, 10:22:44 am »
Félicitation, très belle réalisation!  :-+

There might be a market for these kinds of mods. Lots of HP/Agilent equipment are build with very similar LCD displays. Would not be surprised if all of these use the same protocol. Also those with the fading VFD displays.
As you have access to a CNC machine you might consider milling your own segmented digits out of some black plexiglass. Very similar as what is done in cheap LED clocks. They solder the leds directly to the PCB board with the milled-out plexy hot-glued on top. This way you can have any design you want and choose from many more LEDs to suit your color and power consumption needs.
 

Offline macboy

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #50 on: November 16, 2017, 08:53:18 pm »
Excellent work. Looks really really great.
While I do appreciate that you tried to stay with a 1:1 segment-to-segment identical replacement to the LCD, I wonder if you also considered using a graphic display to produce a custom display? With the data decoded, you could easily decode everything to an alpha-numeric string and display on a (e.g.) 256x64 pixel OLED like this one:

This would be more software work but a lot easier mechanically.
 
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Offline niekvs

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #51 on: November 17, 2017, 11:40:01 am »
Excellent work. Looks really really great.
While I do appreciate that you tried to stay with a 1:1 segment-to-segment identical replacement to the LCD, I wonder if you also considered using a graphic display to produce a custom display? With the data decoded, you could easily decode everything to an alpha-numeric string and display on a (e.g.) 256x64 pixel OLED like this one:
This would be more software work but a lot easier mechanically.

But now try to fit that into the space of the original HP device and make it look good. Unless you have an elongated graphics display in the dimensions of the original it's replacing, it's probably going to look very ugly. Your example display would probably fill up only half of the horizontal space available. You may have some additional space and put in a larger display that's mostly hidden by the enclosure, but how elegant would that be? I think the elegance of the OP's solution is how it fits so perfectly and looks as though it should have been there from the start. Great job!
 

Offline 001

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #52 on: November 18, 2017, 11:03:47 am »
Awesome work  :-+
 

Offline USMC_Spike

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #53 on: November 19, 2017, 05:04:25 am »
I also am interested.

I've found that to be a major drawback to the HPs with LCD readouts.
If you are doing work...it's a real pain to read the display.

I have only a cursory understanding of what you've accomplished,
well done.

We have some of the nice CNC machines at school, I assume
they use a standard protocol for programming.

Could use the information for the CNC too.

it's very good stuff!


 
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Offline Icchan

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #54 on: November 19, 2017, 09:03:45 pm »
Oh darn this is great!

I have an 3478A and the display is basically driving me crazy... I really hope you release more details about this project as open source so I could get this otherwise great device to be even better!

I'm mostly intrested in the protocol details and what discreet logic you used to help you out with the SPI compatibility.

I mean it's all about those details and everythign else is how one wants to tackle the issue.

I was considering a graphics LCD myself for the replacement since I don't own a CNC.


Offline xi

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #55 on: November 19, 2017, 11:37:36 pm »
Hi,

I am back from my business trip, I will answer the questions and post more details (schematics, ...) on the upcoming week. I have already posted the protocol, I hope everything is clear?
I will also see if I can provide some replacement kits at a reasonable price.

Thanks for all your comments and for the post on hackaday ;)
(I am currently mounting the red version of the display)

Xavier
 

Offline vgskb4

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #56 on: December 16, 2017, 06:51:56 am »
Great job on this mod!

Thanks for sharing your work.
 

Offline mlefe

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #57 on: December 24, 2017, 04:17:05 pm »
Excellent work!! Great skills :)
 

Offline dxl

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #58 on: January 03, 2018, 11:48:12 am »
Awesome Work on reversing this. I'm thinking of replacing the display in my HP 4263A LCR Meter, which is (i guess) the same kind of display. This will save me a lot of work :-). I thought someone did the replacement in the 4263A already, but can't find the thread.

Regards
dxl
 

Offline 5065AGuru

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #59 on: January 05, 2018, 05:28:54 am »
 :clap:
VERY nice! The guys at Time Nuts have complained about displays for the 53131A/53132A counters going bad. This would be a very popular fix for those units!!!
Cheers,

Corby
 

Offline Inverted18650

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #60 on: January 05, 2018, 05:34:34 am »
Great work mate and I'm sure you've just inspired many more to follow. :-+

Offline O_Shovah

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #61 on: April 11, 2018, 06:28:55 pm »
I really appreciate the work of Xavier for this great substitute for the HP series.
Here is a HP3457A, a Agilent 4263B and others lacking in the Display department.

@Xi

May i kindly ask you to post/share the firmware and the layouts of your PCB as you proposed.
I would be interested in ordering a batch of PCBs so we could share those as a starting point
for the people who haven't got access to a milling machine. :)

Best regards

Jens
 

Offline pelule

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #62 on: April 11, 2018, 07:52:40 pm »
As far as I know, thats the same LCD Display module used in the HP 6624 Power Supplies (the "tank").
I planned to replace that module as it's readability is quite bad - thus your great work may help a lot to make that project reality.
/PeLuLe
You will learn something new every single day
 

Offline xi

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #63 on: April 22, 2018, 09:45:21 pm »
Hello,

I finally found some time for cleaning my program, so, attached to this message you will find the source code for the ATMega162 that I used for my HP 3457A LED display ;)
https://www.eevblog.com/forum/projects/led-display-for-hp-3457a-multimeter-i-did-it-)/?action=dlattach;attach=415101
It is distributed under the open source GPL licence, please comply with it.

I am also including the complete schematic, also attached to this post: https://www.eevblog.com/forum/projects/led-display-for-hp-3457a-multimeter-i-did-it-)/?action=dlattach;attach=415104

As for the PCB, since there were some demand, I tried to make it manufactured, here is the result:

As you may have noticed, they did it completely wrong |O They didn't follow my instructions (wrong dimensions), neither they worried about drilling all the holes at 0.8mm diameter, telling me that my files were wrong (the same files that I used to make my prototype ::)). Anyway, this is still in progress, and for now I want to keep the PCB design and try to make a kit with it. If it doesn't work, I will provide the PCB files too in the future.

Other news about the display are:
As suggested by tggzzz, I measured the AC noise across a 100k resistor with the LCD display and just after with the LED display, the good news is that I can't see any difference in the value measured between the two displays!


Also made the red version version of the display, using the High Luminosity (Kingbright Super Bright Red PSA39-21SRWA) version of the 14 digits displays:

The result is both nice and a bit disappointing, because these display are not really brighter than the normal version. To be more precise: they can be much brighter, but the segments lit will leak on the other segments that are off ... I initially though that there were some commutation latency problems with my board, but no, in fact the compartment between each digit let pass the light, like on my photo below:

(Only one digit is lit trough a 1k2 resistor 5V => about 3mA ; as you can see, surrounding digits are also lit a bit, even-though they are not powered (one of them is even shorted)).

So the only advantage of this High Luminosity version is that it consumes less power!
« Last Edit: April 22, 2018, 09:49:29 pm by xi »
 
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Offline cheeseit

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #64 on: April 23, 2018, 05:40:00 pm »
This is an awesome project and I've been following it for some time, even though I don't (yet) own a 3457. If I did, I would totally buy a kit and I hope that you're able to make a bit of money off it! Well done! :clap:
 
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Online Specmaster

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #65 on: April 23, 2018, 06:31:19 pm »
Agreed, you have done an awesome job with the and deserve to make at least some money from it. I'm not sure if you are aware of this or not but the links you provided do not work?
Who let Murphy in?

Brymen-Fluke-HP-Thurlby-Heathkit-Thander-Tek-Extech-Black Star-GW-Advance-Avo-Kyoritsu-Amprobe-ITT-Robin-TTi
 
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Offline TERRA Operative

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #66 on: June 29, 2018, 06:41:48 pm »
If you decide to sell PCB's etc, you have a guaranteed sale here! :)
Any circuit design must contain at least one part which is obsolete, two parts which are unobtainable, and three parts which are still under development.

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Offline bitseeker

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #67 on: June 30, 2018, 02:33:21 am »
You know a forum is big when you've missed an awesome hack like this for so long.

Great job, Xavier! I must say I like the yellow display more than the red, even if there wasn't light bleed. For some reason the yellow LEDs go better with the look of the 3457A.
TEA is the way.
 

Offline precaud

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #68 on: June 30, 2018, 01:11:18 pm »
I must say I like the yellow display more than the red, even if there wasn't light bleed. For some reason the yellow LEDs go better with the look of the 3457A.

Same here. Our eyes are more sensitive in the green part of the spectrum. So even with equivalent luminance, the yellow would appear to us to have better contrast.
 

Online intabits

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #69 on: July 05, 2018, 04:15:35 am »
Xi, that is fantastic work you have done there!

Thanks very much for your efforts in decoding the protocol and making your findings available.
I've only skimmed what you've provided, but it looks scary complicated at first glance.

I have three HP3468A's, and I can't stand the LCD displays on them.

They seem to use the same part for the display as yours, with the same signals, so your project is of great interest to me.
I can't find the part (5061-1166) in the HP3457A manual, as it seems to be part of a larger assembly.

The processor in the 3468A is different (1820-2718), an 8039 (from the Intel MCS-48 family), but it's also used in other HP test gear.

I have been thinking about something similar for the last year, and just found this thread, which tells me that it's doable.
But the approach I've been thinking of has differences:-
* Use OLED display(s)
* Hack the firmware, replacing the display protocol entirely.
(among other possibilities that this would enable, the cal values could be saved in EEPROM, rather than depending on the battery backed RAM)

To this end, I wrote a "smart, interactive" disassembler for the 8039, so that I could see how it talked to the display.
The disassembler still needs more work, so almost no progress on unraveling the ROM code so far.
(Member "sailor" was also working on this, and I was hoping to collaborate, but he hasn't been here in over a year)

In any case, your protocol "specification" will be invaluable in deciphering the contents of my ROM, thanks again.
 

Offline mcinque

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #70 on: July 05, 2018, 04:22:34 pm »
That's talent.
 

Offline fenugrec

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #71 on: November 11, 2018, 05:49:48 pm »
Awesome work, xi. I've worked on the 3478A firmare and can confirm almost exactly the same LCD protocol, with one minor interpretation difference.
In the code, they send instruction words as 8-bit bytes, so for instance "0x0A" for "write reg A". The 2 bits difference is easily explained : in your analysis you shift in the 2 bits (always 0) sent while "CS" is high.

In the end it makes no difference though, the actual data exchanged seems identical.

Also, I've emulated the 3478A to a limited extent in MAME , for testing firmware hacks. Current status is rough WIP, no keypad, AD LINK FAIL (of course), no CAL RAM, no GPIB.

 
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Offline bitseeker

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #72 on: November 12, 2018, 02:33:44 am »
A MAME DMM? That's cool.
TEA is the way.
 

Offline McBryce

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #73 on: November 26, 2018, 11:30:39 am »
Seriously cool mod.

I turned on my 3478A last night and noticed the black crystals have started to leak from the bottom left  :--
So add me to the list if you start selling kits.
I'd actually prefer to stay with the original LCd, but I doubt I'll be able to find a drop-in replacement.

McBryce.
« Last Edit: November 26, 2018, 11:32:21 am by McBryce »
 

Offline rastro

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #74 on: November 26, 2018, 03:48:03 pm »
...
I'd actually prefer to stay with the original LCd, but I doubt I'll be able to find a drop-in replacement.

McBryce.

You may want to look at taking the LCD from an hp 3488a - it think they are interchangeable (but you should verify).  You can usually find these pretty cheap on eBay.  However shipping it is sometimes more than the unit costs.  However you might see if the seller will just ship the front panel or display PCB since that would lower shipping cost.  There is not much in HP 3488A unit so you wouldn't be losing much junking the rest of the unit if you are just interested in the LCD.

I just saw two on ebay (unfortunately for Europe buyer it is in the US) for $15.00 but shipping in US about $20.00.

rastro
 

Offline TERRA Operative

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #75 on: November 27, 2018, 03:36:53 am »
I wonder how hard it would be to get a Chinese manufacturer to make some replica LCD panels, along the lines of what Dave did for his uCurrent.
I wonder what the general minimum quantity is on this sort of thing?

Not as cool as the LED's, but maybe more easily accessible pending final cost.....
Any circuit design must contain at least one part which is obsolete, two parts which are unobtainable, and three parts which are still under development.

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Offline bitseeker

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #76 on: November 27, 2018, 03:48:05 am »
It seems getting them made isn't a problem. It just depends on the amount (cost and quantity) required.
TEA is the way.
 

Offline TERRA Operative

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #77 on: November 27, 2018, 04:07:29 am »
Yeah, 100-odd is doable, but 1000 or more is stretching it whether you'd even sell them all...
Any circuit design must contain at least one part which is obsolete, two parts which are unobtainable, and three parts which are still under development.

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Offline floobydust

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #78 on: November 27, 2018, 04:56:37 am »
I think the deal breaker, as far as mass-producing this really neat retrofit, is milling the LED displays to get the width down by 1mm and leave room for discrete colons and comma.
Throwing numbers out there...

OP used Kingbright PSA39-21 0.39" displays about $1.15 each 1000-lot X 12 digits  = $14

For a custom LED display, I imagine it's the NRE to get a custom injection mold made and the custom LED die mounts.
Say it's $10,000 and good for a 4 digit module, need 3 per multimeter and you sell enough for 333 retrofits, total 1,000 pcs. of a custom 4-digit module.
That would make the NRE $10 per (4-digit) display module, and then add the LED module's cost to that, say $11 ea. so $21 per module ($63 per DMM) and $21,000 outlay then.

Someone would have to hit up some LED manufacturers and see if my guess is far off.

Kingbright SMT LED display ACPSA04 is 9.3mm wide vs the original through-hole 9.9mm-1mm milling... I wonder if that would work? It's not as thick too.
 

Offline texaspyro

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #79 on: November 27, 2018, 05:47:37 am »
Use standard SMT LEDs on a PCB to make the segments.  3D print a housing for 7-seg digits.  Maybe fill segments with clear resin.
 

Offline fenugrec

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #80 on: November 27, 2018, 05:54:04 am »
is milling the LED displays to get the width down by 1mm and leave room for discrete colons and comma.
Throwing numbers out there...
Indeed, but I think @TERRA meant manufacturing *LCD* panels, like Dave's multimeter with a custom vector drawing of the segments, etc.
 

Offline bitseeker

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #81 on: November 27, 2018, 06:14:35 am »
Correct, fenugrec. Nevertheless, both possibilities are certainly interesting for the various HP equipment from this era.
TEA is the way.
 

Offline McBryce

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #82 on: November 27, 2018, 08:02:29 am »
...
I'd actually prefer to stay with the original LCd, but I doubt I'll be able to find a drop-in replacement.

McBryce.

You may want to look at taking the LCD from an hp 3488a - it think they are interchangeable (but you should verify).  You can usually find these pretty cheap on eBay.  However shipping it is sometimes more than the unit costs.  However you might see if the seller will just ship the front panel or display PCB since that would lower shipping cost.  There is not much in HP 3488A unit so you wouldn't be losing much junking the rest of the unit if you are just interested in the LCD.

I just saw two on ebay (unfortunately for Europe buyer it is in the US) for $15.00 but shipping in US about $20.00.

rastro

Can anyone here confirm that the 3488 LCD is compatible with the 3478?

McBryce.

Edit: Forget the question, they are not the same. The 3478 has text along the bottom row (SRQ, LSTN, TLK etc), the 3488 has just arrows.
« Last Edit: November 27, 2018, 08:07:20 am by McBryce »
 

Offline TERRA Operative

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #83 on: November 27, 2018, 08:26:19 am »
Yeah, maybe discreet SMD LED's with a 3D printed frame for the segments sounds like a doable idea.
I wonder if a stack of a few PCB's could have the cutout shapes routed out and used the same way?
Any circuit design must contain at least one part which is obsolete, two parts which are unobtainable, and three parts which are still under development.

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Offline rastro

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #84 on: November 27, 2018, 06:11:54 pm »
...
I'd actually prefer to stay with the original LCd, but I doubt I'll be able to find a drop-in replacement.

McBryce.

You may want to look at taking the LCD from an hp 3488a - it think they are interchangeable (but you should verify).  You can usually find these pretty cheap on eBay.  However shipping it is sometimes more than the unit costs.  However you might see if the seller will just ship the front panel or display PCB since that would lower shipping cost.  There is not much in HP 3488A unit so you wouldn't be losing much junking the rest of the unit if you are just interested in the LCD.

I just saw two on ebay (unfortunately for Europe buyer it is in the US) for $15.00 but shipping in US about $20.00.

rastro

Can anyone here confirm that the 3488 LCD is compatible with the 3478?

McBryce.

Edit: Forget the question, they are not the same. The 3478 has text along the bottom row (SRQ, LSTN, TLK etc), the 3488 has just arrows.

You are correct.  I was thinking it is a possible replacement for the HP 3457 which does use arrows like the 3488. 

It slipped by me you were taking about an HP 3478; a different meter from the one of the OP referenced.  Sorry for the confusion.

rastro
 

Offline enochRoot

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #85 on: August 19, 2019, 12:43:57 pm »
Hello Xi,

Not sure if you saw but I sent you a PM.  Interested in any progress on the kit for this.  Would love to inject some visibility into my 3457!

 

Offline coldframe

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #86 on: September 01, 2019, 03:10:44 pm »
Shut Up And Take My Money!
 
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Offline k007007

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #87 on: January 29, 2020, 10:05:31 pm »
Hello!
Really nice job by Xi on both decoding the protocol and building the replacement display!
However, as long as no kit for a LED display appears to be available, this solution might be too consuming for some of us.
A compromise way might be a graphical LCD or OLED.
There is another hurdle though at this way: apparently both 3457A and 3478A send O and S instead of 0 and 5 to LCD. This will make alphanumeric messages look ugly on any display, which presents S and 5 differently; probably there is no chance to "guess" between 5 and S (respectively 0 and O) in the display's controller.
Fenugrec's (https://www.eevblog.com/forum/testgear/hp-3478a-rom-modification-relative-mode/msg2048623/#msg2048623) excellent disasm of 3478A makes chances better at least for 3478A:
hier https://github.com/fenugrec/hp3478a_utils/blob/master/ROM_disasm/dc118.d48#L3965 might be the routine substituting those two bytes.
Though it is not quite clear, why or how 5 is passed to that routine as number 0x05 rather than as symbol 0x35.
Any thoughts or deeper insights greatly appreciated.
 

 

Offline fenugrec

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #88 on: January 29, 2020, 10:59:42 pm »
might be the routine substituting those two bytes.
Though it is not quite clear, why or how 5 is passed to that routine as number 0x05 rather than as symbol 0x35.
Any thoughts or deeper insights greatly appreciated.

You must also look at the code for "render_reading" around 18AD, which takes the packed-BCD reading and prepares the "string" to be sent to the LCD.
Now keep in mind I haven't looked at 8039 asm and this project in a while -
but see how it calls "append_hsdigit" or _lsdigit to go through both upper and lower nibbles of each byte containing packed-BCD.

And later in the implementation of those :
Code: [Select]
append_digit:
anl a,#0xf ; 1d25 - 53 0f S.
orl a,#0x30 ; 1d27 - 43 30 C0
append_tail:
jc X1d2e ; 1d29 - f6 2e v.
mov @r1,a ; 1d2b - a1 !
inc r1 ; 1d2c - 19 .
ret ; 1d2d - 83 .
;
X1d2e: mov r7,a ; 1d2e - af /
xrl a,#0x30 ; 1d2f - d3 30 S0
jz X1d3e ; 1d31 - c6 3e F>
xrl a,#0x5 ; 1d33 - d3 05 S.
jnz X1d39 ; 1d35 - 96 39 .9
mov r7,#0x13 ; 1d37 - bf 13 ?.
X1d39: sel mb0 ; 1d39 - e5 e
call X17ca ; 1d3a - f4 ca tJ
sel mb1 ; 1d3c - f5 u
ret ; 1d3d - 83 .
;
X1d3e: mov r7,#0xf ; 1d3e - bf 0f ?.
jmp X1d39

see how "orl   a,#0x30" would appear to transform digits to "ASCII" numbers (0x30-0x39), but immediately after, you have two XOR operations with 0x30 and 0x05 which seem to do exactly as you describe: check if =='0' or '5' and replace with O/S. (keep in mind the LCD character map has 0x01-0x1A mapped as uppercase letters. (?? see detailed charmap that someone posted earlier)

I still think it would be a better project to emulate some of the code from a modern mcu and replace the display + cal code with something easier to work with. Luckily  my display still works so I don't need to worry about that !
« Last Edit: February 03, 2020, 12:50:11 am by fenugrec »
 
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Offline k007007

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #89 on: January 30, 2020, 01:17:07 am »
Ok, thank you!
now it's clear.
 

Offline graybeard

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    • Chris Grossman
Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #90 on: February 02, 2020, 09:36:29 pm »
excellent work!

Offline dietert1

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Re: LED display for HP 3457A multimeter - I did it :-)
« Reply #91 on: June 16, 2021, 06:54:34 pm »
Today i found this quick fix using pieces of 24 V LED strip. These meters will be in a stationary setup for a long time and i needed illumination for debugging GPIB control.

Regards, Dieter
« Last Edit: June 16, 2021, 06:58:29 pm by dietert1 »
 


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