Author Topic: HP 34401a DMM with leaking segments  (Read 16723 times)

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Offline HighVoltage

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Re: HP 34401a DMM with leaking segments
« Reply #50 on: June 22, 2018, 12:00:42 pm »
Really nice job!
Looking forward to your final design.
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Offline bitseeker

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Re: HP 34401a DMM with leaking segments
« Reply #51 on: June 22, 2018, 09:03:21 pm »
I second what HV said.

Somewhere, I have some Noritake dot matrix VFDs. I think they're 40x2 or maybe 40x4; don't quite remember. If I find them, I'll have to see if they might fit on some of the HP devices I have (DMMs and power supplies). Although replacement isn't necessary now, eventually they might need them.
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Offline qu1ck

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Re: HP 34401a DMM with leaking segments
« Reply #52 on: June 25, 2018, 12:18:17 am »
All right, here it is. Behold: the secret feature unveiled :D

https://youtu.be/LWxOfaXVN3I

That's right. It's a 240 positions resolution, 20fps bar graph. Supports signed and unsigned measurements.
For high fps you have to switch to 4 digit mode. In 5 and 6 digit modes you get 2-3 fps. You can see fps counter in top right on the display.

Pic of an unsigned measurement:
« Last Edit: June 25, 2018, 12:20:18 am by qu1ck »
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Offline wictor

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Re: HP 34401a DMM with leaking segments
« Reply #53 on: June 25, 2018, 06:54:31 pm »
Nice work!
 

Offline bitseeker

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Re: HP 34401a DMM with leaking segments
« Reply #54 on: June 25, 2018, 10:45:56 pm »
I love it! :clap: Makes me want to buy another 34401A, but with a bad display, to upgrade it.

Next secret features: graph and histogram? ;D
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Offline HighVoltage

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Re: HP 34401a DMM with leaking segments
« Reply #55 on: June 26, 2018, 07:00:03 pm »
I have a broken 34401A with a bad VFD laying around, would be nice to test !

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Offline qu1ck

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Re: HP 34401a DMM with leaking segments
« Reply #56 on: June 26, 2018, 09:38:57 pm »
bitseeker
I considered a graph but decided against it (at least for now) because 1) 64 pixels vertical resolution makes a graph not that useful and 2) display does not support horizontal scrolling so I would have to refresh big poligon every time. I'm not sure if I have time budget between text refreshes for that.

HighVoltage
Are you asking for firmware? If you want to reproduce this experiment I can provide wiring diagram and a binary. Source is not ready for public yet.
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Offline bitseeker

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Re: HP 34401a DMM with leaking segments
« Reply #57 on: June 27, 2018, 01:49:08 am »
bitseeker
I considered a graph but decided against it (at least for now) because 1) 64 pixels vertical resolution makes a graph not that useful and 2) display does not support horizontal scrolling so I would have to refresh big poligon every time. I'm not sure if I have time budget between text refreshes for that.

I was partly joking, but for future exploration, a higher resolution screen might make it feasible. The need for hardware scrolling is a good point. It's fun thinking about the possibilities.
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Offline qu1ck

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Re: HP 34401a DMM with leaking segments
« Reply #58 on: June 27, 2018, 02:58:35 am »
High resolution has drawbacks too, either big pixel density (single pixel line not visible from typical distance) or big size and definitely price. Also you will have to go back to lcd most likely so add low contrast to the list.

I even thought of doing the whole thing on esp8266 and stream data to any mobile device/pc. Then you can have any graphs you want. But that is also a lot of software to write and I'm in this business for the rosin smoke lol. When I publish the protocol maybe someone else will do it. Esp8266 has probably enough speed for it.
Although another reason I didnt start with esp is I didnt want a rf antenna inside the metal can that is 34401a generating lots of reflections and affecting measurements god knows how.

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Online TiN

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Re: HP 34401a DMM with leaking segments
« Reply #59 on: June 27, 2018, 04:39:52 am »
qu1ck
Awesome works, keep it up.
Extra thumbs-up for making (or planning) to make it open to community.
I'd love to have similar one for my Keithley 6485 and 2182A here, which use UART datalink to FP too.  :-+

Hate ugly single-line Keithley VFD.  :--
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Offline bitseeker

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Re: HP 34401a DMM with leaking segments
« Reply #60 on: June 27, 2018, 05:32:50 am »
I even thought of doing the whole thing on esp8266 and stream data to any mobile device/pc. Then you can have any graphs you want. But that is also a lot of software to write and I'm in this business for the rosin smoke lol. When I publish the protocol maybe someone else will do it.

Yep, was just brainstorming, rather than intending for anyone in particular to implement. Thanks for making the project open. :-+
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Offline qu1ck

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Re: HP 34401a DMM with leaking segments
« Reply #61 on: July 06, 2018, 11:05:50 am »
Had a productive couple of days on holidays.
Git log:
* b4a62e0 (HEAD -> master) Fix blink interrupt bug
* f16535b Hide bar in menus
* dbaedcc Implement blinking chars
* 016474b Overhaul decoder, separate event handler logic
* 9033e10 Improve init sequence
* 2e2d7ea Clean up display lib
* c055959 Wrap things in namespaces
* 531cf67 More main.cpp cleanup

I implemented one of the last main lacking features, blinking characters. The display is quite usable now. There are some niceties left like better fonts and correctly aligned glyphs but I'm really close now.
Time to start thinking of hardware. I think I'll just remove the filament voltage bias and use that winding of the transformer as power supply for my thingamabob. Haven't tried how the display and blue pill fits inside yet. Hopefully I won't have to do a custom board too, as much fun as that is.
Nothing is true (as far as measurements go)
and everything is permitted (as long as you are ok with magic smoke escaping)
 

Offline bitseeker

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Re: HP 34401a DMM with leaking segments
« Reply #62 on: July 06, 2018, 06:01:09 pm »
Thanks for the update. Yeah, hopefully it all fits nicely inside. Keeping my fingers crossed.
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Offline qu1ck

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Re: HP 34401a DMM with leaking segments
« Reply #63 on: July 07, 2018, 08:04:20 am »
Wrote bmp file to binary convertor and now we have proper icon support. See debug image below with all annunciators lit (diode and continuity are icons).


Funny thing, MS paint is the only (free) program that still supports monochrome bmp that I could find. And it has a bug where you can't paint in white with pencil tool :D
Nothing is true (as far as measurements go)
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Offline HighVoltage

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Re: HP 34401a DMM with leaking segments
« Reply #64 on: July 07, 2018, 08:21:06 am »
Very nice and impressive work!

How does it show up, if you put the Agilent window in front of your display.
Is it still readable?
Or do you rather have to use a clear custom window?
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Offline qu1ck

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Re: HP 34401a DMM with leaking segments
« Reply #65 on: July 07, 2018, 09:14:03 am »
HighVoltage
I'm going to find that out tomorrow when I take the multimeter apart again to do the fitting of the display and mcu board. From what I remember when I disassembled front panel earlier that window is just light blue acrylic (or some kind of plastic) and it should just tint my display in light blue but that's it.
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Offline bitseeker

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Re: HP 34401a DMM with leaking segments
« Reply #66 on: July 07, 2018, 06:54:55 pm »
Wrote bmp file to binary convertor and now we have proper icon support. See debug image below with all annunciators lit (diode and continuity are icons).


Excellent work. I really like how this turned out. Yours is the first successful matrix screen (LCD or OLED) implementation I've seen.

Quote
Funny thing, MS paint is the only (free) program that still supports monochrome bmp that I could find. And it has a bug where you can't paint in white with pencil tool :D

You can make them with GIMP as well. In the current version, go to the Image menu, select Mode, then Indexed. In the Indexed Color Conversion dialog, select "Use black and white (1-bit) palette." When you're done, export the image in Windows BMP format (saving, on the other hand, uses GIMP's native format).
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Offline qu1ck

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Re: HP 34401a DMM with leaking segments
« Reply #67 on: July 08, 2018, 05:40:00 am »
bitseeker
Thanks for the tip, I found a plugin for paint.net can do it too so I'm using it now. GIMP's ux makes my skin crawl.

I took the multimeter apart and did a whole lot of measurements.
TLDR is I'll have to do a custom board.

All measurements in mm
Viewport dimensions (cutout in front panel plastic): 143.5x27
Useable width of the viewport (metal chassis takes away few mm on the left) ~137mm
OLED display board dimensions: 100.5x33.5
Blue Pill mcu board dimensions (without jtag header, board only): 53x23

In terms of height everything fits fine, the original display has a metal shroud that is 35mm, new display board will fit there easily.
Depth is tight but should be ok too. Old display has distance board to top of glass of 13.3mm but it sits in a little recess in the viewport. New display doesn't fit in that recess so I have to fit into 11.5mm of depth. And there is that fat DIP42 UPD7527 that takes 4-4.2mm of space under display. So there is ~7.3 left. New display is 6.5mm deep, including components on back side.
Problem is width. As you can see 53 + 100.5 > 137 by quite a bit. You can win 6-8mm by moving display to the right so that the board edge and part of display bezel edge is not in the viewport but it is still not enough.
If you overlap left part of display board with mcu board and chop off the jtag header part completely (may have to sacrifice LEDs too) then maaaybe it will fit. But that is too barbaric for my taste.

So next thing i'll focus on is designing custom board. It's a shame, many people are afraid of soldering 0.5mm pitch qfps so it will limit this mod's accessibility for a hobbyist. I just hope that the kind of people that have this type of instrument are advanced enough in the soldering department that it won't be much of a deterrent. With custom board I will be able to stick the USB out through a small cutout in the front window panel. That will make firmware updates so much easier.
And no, arduino pro mini while being smaller doesn't have the speed. 8bit AVRs suck these days, their only upside is availability in easily soldered packages.

On the bright side, the display is quite, well, bright :D even behind the original tinted window. It doesnt even tint it blue, just decreases the contrast a bit.
Without the window both displays have approximately the same contrast and brightness.
Nothing is true (as far as measurements go)
and everything is permitted (as long as you are ok with magic smoke escaping)
 
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Offline HighVoltage

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Re: HP 34401a DMM with leaking segments
« Reply #68 on: July 08, 2018, 07:39:52 am »
It looks very nice readable behind the original window.
Very nice job!
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Offline bitseeker

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Re: HP 34401a DMM with leaking segments
« Reply #69 on: July 09, 2018, 05:13:29 am »
bitseeker
Thanks for the tip, I found a plugin for paint.net can do it too so I'm using it now. GIMP's ux makes my skin crawl.

Yep, always good to have options.

Quote
I took the multimeter apart and did a whole lot of measurements.
TLDR is I'll have to do a custom board.

I kind of figured that might happen. However, you can then get things just the way you want them.

Quote
So next thing i'll focus on is designing custom board. It's a shame, many people are afraid of soldering 0.5mm pitch qfps so it will limit this mod's accessibility for a hobbyist. I just hope that the kind of people that have this type of instrument are advanced enough in the soldering department that it won't be much of a deterrent.

Hopefully, they didn't blow their budget getting the 34401A and can get a hot air station, if they don't already have one.

Quote
On the bright side, the display is quite, well, bright :D even behind the original tinted window. It doesnt even tint it blue, just decreases the contrast a bit.
Without the window both displays have approximately the same contrast and brightness.


That's good news. I was afraid that the filter would be too dark. It looks fine.
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Online zucca

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Re: HP 34401a DMM with leaking segments
« Reply #70 on: July 09, 2018, 07:12:00 am »
qu1ck, impressive. Somebody should give you a Keithley 2xxx when you are done with the 34401a.  ::)

Congrats.

TLDR is I'll have to do a custom board.

Probably you will sell a truck of them. Please consider a group order.
Is it possible to squeeze in it a RS232-USB or Serial Bluetooth/WIFI Ethernet (for remote logging) adapter in it? I am thinking how to use the extra space in the front wisely. Also a bigger diplay with the opportunity to placing some fixed label on the side could be neat, with multiple 34401a on the bench knowing what is measuing what with display labels is nice to have. Don't know how to upgrade the labels, probably all my ideas are too complicated to realize.

Maybe creating a dedicated thread in the test&equipment is also a nice call, so other people could tip in.
« Last Edit: July 09, 2018, 09:00:59 am by zucca »
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Offline bitseeker

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Re: HP 34401a DMM with leaking segments
« Reply #71 on: July 09, 2018, 05:42:15 pm »
With custom board I will be able to stick the USB out through a small cutout in the front window panel. That will make firmware updates so much easier.

Is it possible to squeeze in it a RS232-USB or Serial Bluetooth/WIFI Ethernet (for remote logging) adapter in it? I am thinking how to use the extra space in the front wisely.

It seems that these two USB ideas go well together conceptually. Having the port in the front only for updating firmware seemed unnecessary (could just have it inside), but if the port is available for logging, too, then that'd be great.


Also a bigger diplay with the opportunity to placing some fixed label on the side could be neat, with multiple 34401a on the bench knowing what is measuing what with display labels is nice to have. Don't know how to upgrade the labels, probably all my ideas are too complicated to realize.

qu1ck said that he's making this project open, so there may be lots of interesting things to come.
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Offline qu1ck

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Re: HP 34401a DMM with leaking segments
« Reply #72 on: July 09, 2018, 07:41:54 pm »
Probably you will sell a truck of them. Please consider a group order.
Doing logistics of group order and delivery is not worth it to me. Board designs as well as everything else will be open so anyone can do it.

Is it possible to squeeze in it a RS232-USB or Serial Bluetooth/WIFI Ethernet (for remote logging) adapter in it?
Yes, stm32f103 usb port works as a serial port. For now it is only used to upload firmware and monitor debug messages but it's entirely possible to send a properly formatted data out of it and/or send commands back. You won't be able to emulate button presses though, my board only listens on the data lines.

Also a bigger diplay with the opportunity to placing some fixed label on the side could be neat, with multiple 34401a on the bench knowing what is measuing what with display labels is nice to have. Don't know how to upgrade the labels, probably all my ideas are too complicated to realize.
Bigger display will likely not fit, they are a lot more expensive too. Labels are easy to do, I can display them instead of the bar graph below. I think I'll add that feature. You'll be able to set/update/unset label via usb serial command.

Having the port in the front only for updating firmware seemed unnecessary (could just have it inside), but if the port is available for logging, too, then that'd be great.
Having port easily accessible is super useful for development. I upload firmware 10-20 times during each coding session. Having multimeter taken apart all the time would be PITA.
But yes, the port also streams display data.
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Offline floobydust

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Re: HP 34401a DMM with leaking segments
« Reply #73 on: July 09, 2018, 07:42:29 pm »
I reverse engineered the 34401-66502 front panel PCB mechanical a while ago, it was no fun. Many hours with calipers, lots of slots...

HP's mechanical engineering here has many innovations, actually very good engineering when you dig in.
The PCB sliding in and snapping into place (no fasteners) with a conductive rubber keypad, a complex difficult plastic mold to reduce costs- impressive work.

At the time I thought I had a failed uPD7527 and was designing a replacement front panel PCB that would still use the VFD but with a new MCU and VFD driver. This is for a simple Gen1 34401-66502 replacement. Not to be confused with Gen2 34401-66512 front panel PCB that uses 87C51 and SN75518's and requires different DMM firmware.
I have another 34401a to repair with the polka-dot problem, waiting for parts to arrive. If it is the NEC MCU then I will just finish the replica PCB.
 

Offline bitseeker

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Re: HP 34401a DMM with leaking segments
« Reply #74 on: July 09, 2018, 11:38:56 pm »
It'd be nice to combine qu1ck's display with flooby's replica front panel PCB. However, handling of the buttons would still need to be added, right? I assume that's what's meant by "finish the replica PCB."
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