Author Topic: HP3548 / HP3457 OLED display (Read 11399 times)

Xyphro · « **on:** February 01, 2022, 08:33:28 pm »

Hi Guys (and Girls),

I have since quite some time a HP3457 multimeter and hate the display. Had to do something about it. The typical LED Backlight mod was not resonating - it looked still very bad - low contrast.

I had to come up with something else. I loved this idea here from Xi: https://www.eevblog.com/forum/projects/led-display-for-hp-3457a-multimeter-i-did-it-)/50/

But mechanical wise it is very hard to reproduce for others (including me).

After many weeks of hunting for OLED screens in the right format I had a brilliant Idea: Why not use the typical small OLEDs that you can get for extremly low price on Aliexpress and use a single display per digit?! Immediately routed a PCB and ordered it and after some months I had time to take this up and program the SW (thanks again Xi for your groundwork in decoding the protocol!).

The current consumption is extremly low, while the display is very bright: only 20mA are consumed.
Instead of isolating the power supply, I isolated the datapath, so it can still be powered from an AC supply in an galvanically isolated way.

The PCB is from JLCPCB. No milling required and a second PCB (which is not shown) acts as a mechanical holder which has mounting holes and can be mounted without any modification of the multimeter. Also the original flatband cable connector can be used.

Work is nearly done. I think I will put everything together tomorrow and share the final pictures :-)

Best regards,

Kai

Edit: Here a very bad quality video of the current state: https://youtu.be/hoUbkyWuI_g

EHT · « **Reply #1 on:** February 01, 2022, 10:58:24 pm »

Looking great! I'd seen the backlight mods but didn't fancy the risk of cracking the display open, and then ending up with poor contrast anyway. A new module mechanically compatible with the LCD is perfect!

free_electron · « **Reply #2 on:** February 01, 2022, 11:40:10 pm »

coooooooool !

Xyphro · « **Reply #3 on:** February 02, 2022, 04:26:14 pm »

Have built it in and I am very pleased with the result.
Now I have to finish the annuciators (small triangles on the bottom of the screen).

Xyphro · « **Reply #4 on:** February 02, 2022, 04:27:32 pm »

Some more Photos...

Hexley · « **Reply #5 on:** February 02, 2022, 05:01:02 pm »

Quote from: Xyphro on February 02, 2022, 04:26:14 pm

Have built it in and I am very pleased with the result.
Now I have to finish the annuciators (small triangles on the bottom of the screen).

That looks really great, Xyphro.
Question: is there enough resolution to display text annunciators below the digits, such as is done in the 3478A? Those vary from three letters, like "TLK" or "RMT", up to five or six, like "SHIFT" or "AZ OFF". If that could be done, your approach could lead to an excellent replacement for the 3478A LCD.

Xyphro · « **Reply #6 on:** February 02, 2022, 05:12:16 pm »

Hmm, Funny. My hp3547 lcd just had arrows pointing down and no Text. Underneath the display there is a Text printed on the frontpanel of the hp3547.

The witdh of the Oled is 32 pixels.

Challenge accepted :-) I have 3KB Flash space left of the total 8KB.

Kleinstein · « **Reply #7 on:** February 02, 2022, 05:42:34 pm »

12 digits time 32 byte for the graphics to display would only 384 bytes of the memory. So in princuple it could work with a little text / symbols.
It is stiff the question if just the same arrow / block for all positions could work as well.

free_electron · « **Reply #8 on:** February 02, 2022, 05:49:15 pm »

Quote from: Xyphro on February 02, 2022, 05:12:16 pm

Hmm, Funny. My hp3547 lcd just had arrows pointing down and no Text. Underneath the display there is a Text printed on the frontpanel of the hp3547.

The witdh of the Oled is 32 pixels.

Challenge accepted :-) I have 3KB Flash space left of the total 8KB.

depends on the vintage of the machine.

i like how you even made the pressfit dip socket. so this is a real replacement for the hp 5 bit drivers.

Xyphro · « **Reply #9 on:** February 02, 2022, 06:04:29 pm »

I'd make it configurable (triangles or different Text variants) . If 32 pixels results in unreadable Text, I can go for 2 line Text.

Xyphro · « **Reply #10 on:** February 02, 2022, 09:10:59 pm »

I think it should work. I designed below icons (Mix of icons for different multiple multimeter types) and converted them to .c / .h. Will try this out tomorrow and post some pictures. The selection between booring triangles and device specific variants can be made during compile time (select 1 icon per digit position).

Xyphro · « **Reply #11 on:** February 03, 2022, 02:02:17 pm »

...and I think I am done!

Now it is possible to select between 3 different flavors:

HP3457_ORIGINAL => Uses triangles as annuciator
HP3457_ICONS => Uses Icons matching HP3457
HP3478_ICONS => Uses Icons matching the HP3478

The Icons I made are well visible, but very hard to read. Allthough it looks nice on the pictures, I would make the Icons a bit bigger if I'd seriously use them. But as the source is a .GIF file it is easy to do that. Maybe in the next days I'll try this out.

Here an updated Video (unfortunately it started looking blury once I uploaded it to youtube): https://youtu.be/EYaLf55-z-o

BTW: On the pictures it looks as if the digits are not perfectly centered towards the labels underneath. Actually it is perfectly aligned. It looks shifted because the camera was very close to the display.

Xyphro · « **Reply #12 on:** February 03, 2022, 02:25:24 pm »

I remeasured the current consumption with the triangular annuciators. When supplied with 12V DC it is 30mA.

There is a 5V Regulator on the Digital Board which is supplied with 12V on its input side where I hooked it up to. So no additional supply is needed.

Dr. Frank · « **Reply #13 on:** February 03, 2022, 04:39:04 pm »

Hello Kai,
great work so far!

Your headline implies that you have another version available, maybe for the HP3458A, or is it just a typo?

Would be great, but you'd need a 16 digit, 12 annunciator version.
Frank

TERRA Operative · « **Reply #14 on:** February 03, 2022, 04:54:22 pm »

If the 3478 version icons can be made to be nicely readable, I'm interested.

Will you sell PCB's? Or provide gerbers etc? I have two, maybe three 3478's that can do with an upgrade...

Xyphro · « **Reply #15 on:** February 03, 2022, 05:38:01 pm »

Good remark Dr. Frank. I though they both have 12 digits :-) the scheme can be scaled, but obviously not with the same PCB. The parallel i2c control would be ready to control 16 displays at 100kHz.

Xyphro · « **Reply #16 on:** February 03, 2022, 05:40:30 pm »

I plan to put it on Github soon. Hp3478 is not tested, but I guess the protocol is not different. A confirmation if it works would be great.

dietert1 · « **Reply #17 on:** February 03, 2022, 07:27:49 pm »

Great work! One could invert those icons though to increase font size and readability, maybe using only three letters if four don't fit.

How does the durability of those OLED displays compare to a VFD?
The best OLEDs nowadays are good for 100 000 hours, that is 11 years. But there are differences. As far as i remember the first OLEDs were good for 2 years only. And as far as i remember they degraded even when not in use (oxygen leaks to organic material).

Regards, Dieter

EHT · « **Reply #18 on:** February 03, 2022, 07:31:00 pm »

Such a professional job! I love that the blue OLEDs even match the colour on the front panel. I'm in for one for a 3457A, if there is likely to be any bulk order of PCBs etc.

Xyphro · « **Reply #19 on:** February 03, 2022, 07:32:38 pm »

About burnin: Not sure, but I had that thought also already. Time will show.

rsjsouza · « **Reply #20 on:** February 03, 2022, 08:09:54 pm »

This is a fantastic mod, Xyphro. I look forward for your design!

Xyphro · « **Reply #21 on:** February 03, 2022, 09:11:39 pm »

About the annuciators: I have tried to increase the textsize a bit and inverted them. Attached a photo for the HP3547 version of the textual icons.
Might still be improved a bit, but I am happy with it.

Edit: A PM reminded me, that I also have A HP6651A power supply with a very similar kind of display. Unfortunately that supply is lying like a ZOMBI (half dead half alive [1]) in a shelf, but still I can try the display out and maybe that stimulates me also to repair the supply...

[1] (one of the very expensive DACs is dead and I lost interest because it is such a heavy beast.)

TERRA Operative · « **Reply #22 on:** February 03, 2022, 11:34:15 pm »

That latest design is much nicer IMO.

I have a few HP power supplies, but the LCD setup is quite different to the meters, so I'm not sure how cross compatible it will be, I can open them up and take a look when the time comes.

EHT · « **Reply #23 on:** February 04, 2022, 12:37:44 am »

Quote from: TERRA Operative on February 03, 2022, 11:34:15 pm

I have a few HP power supplies, but the LCD setup is quite different to the meters

+1: also have 6644A and 6622A PSUs that could benefit from readable displays!

FWIW, the new design with non-inverted annunciators is great!

Xyphro · « **Reply #24 on:** February 04, 2022, 06:44:03 am »

The Hp66xx supplies have mechanical same displays, also with 12 digits. Of course supplies like E3632 and similar ones are very different.

Btw. My hp3547 shows when the input is left open in Volt Mode a very huge drifting voltage until I connect it to a source or I change the input impedance to the lower setting. Is this normal or an indication of something dying?

Berni · « **Reply #25 on:** February 04, 2022, 07:00:50 am »

Wow nice one! It looks great!

I suppose for the HP 3458 it is a bit less attractive since it already has a VFD display(Unless you had high mileage one with a very faded VFD), but for a HP 3457 it sure does make a night and day difference. I always found non backlit LCD screens on test equipment a pain in the ass with how difficult they are to read.

I love VFD style displays on test gear. The new fangled color LCD stuff never looked good to me.

Xyphro · « **Reply #26 on:** February 04, 2022, 07:12:40 am »

Fully agree! Vfd is really great. Actually also looked for 12 digit VFDs btw. before making this (and smaller IPS TFT panels, which unfortunately did not align well with the 12 digit pattern on its 10mm increments).
Some equipment like fluke 289 has a back Light LCD. Allthough it helps, it also reduces the contrast when it is turned on, but it still helps in some situations.

Kleinstein · « **Reply #27 on:** February 04, 2022, 08:36:48 am »

Quote from: Xyphro on February 04, 2022, 06:44:03 am

The Hp66xx supplies have mechanical same displays, also with 12 digits. Of course supplies like E3632 and similar ones are very different.

Btw. My hp3547 shows when the input is left open in Volt Mode a very huge drifting voltage until I connect it to a source or I change the input impedance to the lower setting. Is this normal or an indication of something dying?

In high Z mode a drifting input voltage when open circuit is normal. The 3457 is supposed to have some 220 pF plus some parasitic capacitance at the input. So a 25 pA input current would cause a dirft rate of some 0.1 V per second. If the dirft is considerably large this points to higher than normal input current. This could be from leaking parts, contamination or from a problem with the precharge circuit. The precharge part could be excluded in the non AZ mode.

Xyphro · « **Reply #28 on:** February 04, 2022, 09:42:18 am »

I have to disappoint in the feasibility to reuse this exact same display design as it stands for the HP66xx supplies. Mechanical it is very easy to make it fit (just a notch has to be inserted in the PCB outline). BUT (and a big one) the protocol seems different.

If I'd have all time in the world and this power supply would be extremly interesting for me to get it repaired I'd immediately jump on it to get it done, but I would here prioritize other things first. Maybe.... maybe I'd take this up in future. Decoding it should not be too tough, but time is an issue here.

Xyphro · « **Reply #29 on:** February 04, 2022, 09:42:57 am »

2 more pictures of the supply

Xyphro · « **Reply #30 on:** February 04, 2022, 10:14:12 am »

Actually, after a close look the protocol seems not THAT different.

Pin 9 seems to contain the data sent to the display
Pin 11 is the clock signal
HO2 is the command data stream
HO3 is the SYNC line (HIGH indicates a new command ID beeing sent, low indicates data payload)

HO0 is unknown... maybe some chip select signal?

I just did a very quick screening, but I see commands like 0x028 and 0x2F0 flying by with the above assumption.

There are a lot of unrequired pulses visible (maybe because the HSO bus of the MCU is used for other purposes too), but if you only look at the onces that are sampled on a clock edige of the Pin 11 clock signal it seems to be similar.

So maybe... I have been too negative about my previous statement?!

Attached a saleae logic trace (done with version 1.2.18)

EHT · « **Reply #31 on:** February 04, 2022, 12:55:22 pm »

Quote from: Xyphro on February 04, 2022, 06:44:03 am

The Hp66xx supplies have mechanical same displays, also with 12 digits. Of course supplies like E3632 and similar ones are very different.

Great job checking these out already. For everyone's benefit: on the 6644A, a 16-pin connector J2 on the attached diagram. I couldn't see the equivalent for the 3457A because the copy I have is pretty poor quality.

Quote from: Xyphro on February 04, 2022, 06:44:03 am

Btw. My hp3547 shows when the input is left open in Volt Mode a very huge drifting voltage until I connect it to a source or I change the input impedance to the lower setting. Is this normal or an indication of something dying?

Yes, mine shows this with no input:
* DCV about +1.4V
* ACV about 2mV

voltsandjolts · « **Reply #32 on:** February 04, 2022, 05:25:14 pm »

Well done Kai, using multiple cheap oled displays in that way is a great idea

Hexley · « **Reply #33 on:** February 04, 2022, 05:36:38 pm »

@Xyphro -
In the picture of the board that you posted in reply #4 above, there is a legend on the mounting board that says something like "Short R518 on Main PCB!"

Can you elaborate, please? I'd like to map that onto the 3478A schematic.

Or if you can just confirm the resistor number, I can chase up the 3457 schematic and see for myself; no worries.

Thanks,
hb

Xyphro · « **Reply #34 on:** February 04, 2022, 05:46:33 pm »

Hi!

This shorting is actually not required.

I use an isolator IC to avoid disturbances. That one needs to be supplied with 5V on the input side. The flatband cable to the display has a 5V line but on the HPs Digital PCB there is a series resistor to Limit the current. Depending on which Generation of multimeter you have it is either 1Kohm or 470Ohm.

I have put this remark on my pcb before I checked how low the current consumption of the isolator IC is. It works Perfect without the short circuit.

Best regards,

Kai
Ps: R540 is what I refer to.

Hexley · « **Reply #35 on:** February 04, 2022, 05:56:53 pm »

Quote from: Xyphro on February 04, 2022, 05:46:33 pm

The flat and cable to the display has a 5V line but on the HPs Digital PCB there is a series resistor to Limit the current. Depending on which Generation of multimeter you have it is either 1Kohm or 470Ohm.

I have put this remark on my pcb before I checked how low the current consumption of the isolator IC is. It works Perfect without the short circuit.

It looks like that resistor is 1K in the 3478A (R508). So no need to short it, it seems. That is great. Thank you for the info.

Xyphro · « **Reply #36 on:** February 04, 2022, 06:56:21 pm »

Honestly, if I'd make another redesign I'd remove the isolator also and Power it from the 5V (then with shorted resistor). The 3.3V could be made with an LDO and the 7.5V for the Oled either using its internal chargepump (+1 transistor per oled) or a boost converter.
It would bring the complexity of the schematic down further.

RichardM · « **Reply #37 on:** February 04, 2022, 10:50:22 pm »

This looks great. Thanks.

I have an HP-3468a and was wondering if this modification would also work on it ? I will find the schematics but I had always assumed the 3468a was almost the same as the 3478a but with lower specs and HP-IL ports.

Cheers

Xyphro · « **Reply #38 on:** February 05, 2022, 09:28:33 am »

Looking at the Service manual it might work. But should be tried out. But it is not clear from the manual what Kind of connector they use (16 pin dual row pin header or press fit dip).

Xyphro · « **Reply #39 on:** February 05, 2022, 09:09:46 pm »

Hi @All:

As promissed I have just published all design files to Github:
https://github.com/xyphro/HP3457-OLED-display

Have fun :-)

Best regards,

Kai

Hexley · « **Reply #40 on:** February 05, 2022, 09:16:58 pm »

The pdf schematic in ../hardware/eagle/ renders as though it were a mirror image, at least for me.

Xyphro · « **Reply #41 on:** February 05, 2022, 09:22:27 pm »

Haha, you are right, thanks for feedback. Will fix it :-)
Edit: DONE!

Hexley · « **Reply #42 on:** February 05, 2022, 10:03:46 pm »

Thanks, Kai.

A few more questions:

1. Can you share a part number and/or vendor information for the OLED displays that you used? I am not finding any blue on black versions, only white on black or yellow on black.

2. Your writeup mentions using a TO220 regulator and connecting AC lines to pin 1 and 2. Can you elaborate on this, please?

3. Have you had a chance to think further about what you suggested a while ago in terms of powering +5 directly from the Vcc pin of the 16-pin header (after removing the limiting resistor on the motherboard)?

Thanks for posting to github. It is great to see the details of your work.

tfm · « **Reply #43 on:** February 05, 2022, 10:59:39 pm »

Quote from: RichardM on February 04, 2022, 10:50:22 pm

This looks great. Thanks.

I have an HP-3468a and was wondering if this modification would also work on it ? I will find the schematics but I had always assumed the 3468a was almost the same as the 3478a but with lower specs and HP-IL ports.

Cheers

Hi RichardM, I am in the same situation here. And I'm willing to try it, it should work for both of them.

Xyphro · « **Reply #44 on:** February 05, 2022, 11:00:00 pm »

Hi Hexley,

1.) I ordered those displays: https://m.de.aliexpress.com/item/1005001856921229.html
Or search for: XAbl 0.87 inch oled

2.) I will share a photo tomorrow

3.) I did not investigated this further. With the galvanic Isolation and the option to power it from an AC or DC source you have the most flexibility.

Best regards,

Kai

tfm · « **Reply #45 on:** February 05, 2022, 11:12:26 pm »

Quote from: Xyphro on February 05, 2022, 09:09:46 pm

Hi @All:

As promissed I have just published all design files to Github:
https://github.com/xyphro/HP3457-OLED-display

Have fun :-)

Best regards,

Kai

Thank you so much, @Xyphro! That is a great contribution!

Xyphro · « **Reply #46 on:** February 06, 2022, 01:52:34 pm »

Hi Hexley,

attached a photo that shows how I supplied the display with power.

The regulator U701 gets 12V DC on its input and outputs 5V DC. Pin 1 is the input (+12V), pin 2 is GND, the unconnected pin 3 is +5V.

I simply routed a cable from the AC connector of the new display to the regulator pin 1 and 2. As my display design has a bridge rectifier on its input, it does not matter where you connect +12V or GND to.

Best regards,

Kai
PS: The displays I bought are sold as white on black displays, but actually they look a bit blueish as you can see on the pictures.

Hexley · « **Reply #47 on:** February 06, 2022, 04:55:08 pm »

Thanks, Kai. That is very clear.

More questions:

1. Is there a special method to space the mounting board and the display board from each other when it comes time to solder the interconnecting pins?
2. Do you use anything to hold down the OLEDs to the PCB, like hot glue or super glue?
3. Do you use a jig or template to get the OLEDs centered vertically in the LCD window opening?
4. ~~Did you try pullup resistors on the I2C lines and decide that they were not needed?~~ [Edit: Nevermind; I see how you did the bit banging in software. Clever.]

Sorry to keep pestering you!

- Hexley

Xyphro · « **Reply #48 on:** February 06, 2022, 06:53:35 pm »

No issues, questsions are there to get asked :-)

1.) See 1st attached picture. It is simply the spacing as given by a standard pinheader - not more and not less.

2.) I used doublesided "foam tape". Not sure what the proper american term is for that. It is foam that is sticky on both sides and a bit compressable. See 2nd picture.

3.) for the orientation in Y-direction I had put 2 layers of the "foam tape" at the bottom side. I could nicely hold the OLED against it and then press it down, so that it sticks to the other foam tape. Afterwards I removed those 2 layers of foam tape (white in the picture) again. This is all I did. I did not create a template for it.

4.) I did not use Pullup resistors (a deliberate design choice). This might look hacky of course, but is perfectly OK. Yhe MCU drives I2C in push-pull mode. The SSD1306 will not do clock stretching, so the SCL line is never driven low by the display. The SDA line is driven low by the display only in the ACK phase. In that phase I do switch the MCU to open drain with pullup resistor (but actually don't read the ACK bit). So there are never 2 drivers working against each other on the SDA line. Even if this would happen, the IOs are current limited and no transistors get hurt :-) During development I had this happening a few times of course, but nothing got destroyed.

RichardM · « **Reply #49 on:** February 07, 2022, 08:40:14 am »

Having problems posting so I apologise if this appears twice.

The 3468a appears to use a DIP press fit connector, 2 rows of 8 pins. Do these pull out or are they soldered in after pressing together ? The same connector is used on the other end on the main board.

The annunciations are also attached, the spacing between the screw holes for the LCD board are 149 mm.

How does this compare to the 3478a ?

Cheers

Xyphro · « **Reply #50 on:** February 07, 2022, 11:16:19 am »

It looks exactly as my hp3457a allthough that was not the question you asked. It has the same press fit 2 rows by 8 pins connector. Also the mechanical mounting points look identical.

Xyphro · « **Reply #51 on:** February 07, 2022, 11:17:29 am »

And you can just pull the connector out. It is not soldered, but has a spring mechanism.

Le_Bassiste · « **Reply #52 on:** February 07, 2022, 12:06:35 pm »

Quote from: Xyphro on February 04, 2022, 09:42:18 am

I have to disappoint in the feasibility to reuse this exact same display design as it stands for the HP66xx supplies. Mechanical it is very easy to make it fit (just a notch has to be inserted in the PCB outline). BUT (and a big one) the protocol seems different.

If I'd have all time in the world and this power supply would be extremly interesting for me to get it repaired I'd immediately jump on it to get it done, but I would here prioritize other things first. Maybe.... maybe I'd take this up in future. Decoding it should not be too tough, but time is an issue here.

have a look in https://www.eevblog.com/forum/repair/replace-lcd-on-hpagilent-664xa-psus/msg2137255/#msg2137255, might help figuring out the hp66xx display communication.

Xyphro · « **Reply #53 on:** February 07, 2022, 12:49:48 pm »

Thanks for sharing. Actually the protocol is the same! Just the connector has a different pinout.

Kean · « **Reply #54 on:** February 07, 2022, 01:04:39 pm »

Quote from: Xyphro on February 07, 2022, 11:17:29 am

And you can just pull the connector out. It is not soldered, but has a spring mechanism.

I can confirm. I have my HP 3468A open on the bench, and the DIP connector has split pins which press fit into the PCB. Just be gentle removing it.

I took a quick peek into one of my HP 3478A's, and it has the same display PCB labelled "5061-5212". A google on that brings up lots of hits.

Kean · « **Reply #55 on:** February 07, 2022, 01:08:28 pm »

Hmmm... newer ones seem to use a "5181-2813" display PCB. I wonder what the difference is.
If it wasn't already past midnight here I'd check the service manual.

Xyphro · « **Reply #56 on:** February 07, 2022, 08:04:45 pm »

However this turns out with those multimeter, just want to say you get my full support in adjusting the AVR Software whereever/ifever required :-)
This would especially work well in case you can make logic analyzer dumps. I have a method to play back logic analyzer traces physically.

RichardM · « **Reply #57 on:** February 07, 2022, 09:03:17 pm »

Ok

Does the whole thing come off the board ? Or is half the dip socket remain after removal ? The spring is easy tonremove and suggests half the socket remains ?

Richard

Xyphro · « **Reply #58 on:** February 07, 2022, 09:25:33 pm »

The whole thing comes off the Board, so the cable including all the plastic parts in one piece. Just apply some force between the lcd pcb and the plastic Part where the cable ends up in.
Don't be afraid, it is not a lot of force required.

Best regards,

Kai

Xyphro · « **Reply #59 on:** February 07, 2022, 09:30:29 pm »

Or to explain it differently: after you have the dip press fit removed, the display lcd had no plastic parts, but you just see holes in it. The cable side has all plastic parts and metal spring pins that were pushed before removal into the PCB.

RichardM · « **Reply #60 on:** February 07, 2022, 10:04:00 pm »

Great thanks

I am willing to give this a try on my 3468a.

Regards

Richard

P.S If anyone else in Australia wants to make the same modifications I would be happy to share the PCB costs, I certainly don't need 5 boards

Kean · « **Reply #61 on:** February 08, 2022, 11:41:45 am »

Quote from: RichardM on February 07, 2022, 10:04:00 pm

P.S If anyone else in Australia wants to make the same modifications I would be happy to share the PCB costs, I certainly don't need 5 boards

Richard, Yes! I am in Sydney and have 1 x 3468A and 3 x 3478A. I'd like to try this on at least one of them.

Xyphro · « **Reply #62 on:** February 08, 2022, 01:51:37 pm »

Lucky guys, you have summer, while we have it freezing cold here :-)

Hexley · « **Reply #63 on:** February 08, 2022, 05:04:50 pm »

The datasheet for the OLED display has a section on "Image Sticking" that refers to a ghost image that can remain if a fixed pattern is displayed for long periods.

From the datasheet:
"If you remain a fixed image on OLED Display for a long period of time, you may experience a phenomenon called Image Sticking. Image Sticking - sometimes also called “image retention” or “ghosting”- is a phenomenon where a faint outline of a previously displayed image remains visible on the screen when the image is changed. It can occur at variable levels of intensity depending on the specific image makeup, as well as the amount of time the core image elements are allowed to remain unchanged on the screen."

They go on to say that it is not true burn-in, and can be reversed by displaying a black screen for an extended time. They recommend not showing a fixed display for more than 2 hours.

A DMM display will be a mix of dynamic elements (the numbers) and static elements (the mode letters and the annunciators). The latter may remain unchanged for long periods, and thus invite ghosting.

This suggests that it might be good to add a screen saver mode to the Kai Display. Perhaps something that follows this logic:

1. Create a watchdog timer with a period of, say, 30 minutes. This will determine the timeout period.
2. Start the timer at power on.
3. Restart the timer if there are any signs of activity, such as:
* Any change in the operating mode, as determined by a change in the right-most 4 characters of the display. E.g., if those go from "MADC" to " VAC", that shows the user has interacted with the instrument.
* Any change in the annunciators. E.g., if the "Shift" annunciator comes on, the user has interacted with the instrument.
4. If the timer times out, display a screen saver image, such as:
*Black screen.
*Animated image, e.g. the "flying geese" of the HP41 calculator.
5. When in blanked mode, unblank (restart the timer and restore the normal display) if any user activity is detected. See step 3 above.

The screen saver function could be enabled/disabled by a jumper, perhaps. The parameters suggested above would need tweaking, no doubt -- exactly which annunciators should be monitored, for example.

There are probably some corner cases that would allow an undesired timeout, or perhaps prevent a desired timeout. But for the majority of uses, the algorithm above would probably work adequately, or so it seems to me.

I'm curious what others might think about this.

Xyphro · « **Reply #64 on:** February 08, 2022, 06:16:03 pm »

Agree, this would prevent issues. About 2008 when I used oleds the first time there were recommendations to limit burnin of pattern like shifting every few second the picture by a Pixel or so,... I hope those oleds are better, but I cannot tell that by experience.

The SW can certainly detect if the content did not change over the last x minutes and then darken the display, turn it off,... And on again when something in the content changed. Maybe the sample annuciator should be ignore then or a smarter time out method found.

I can do something in the Software if we agree on a scheme and reaction.

Possible actions I can imagine
- blank screen
- dim screen
- shift over time every few seconds/minutes the screen content up and down very few pixels

RichardM · « **Reply #65 on:** February 08, 2022, 09:09:35 pm »

Quote from: Kean on February 08, 2022, 11:41:45 am

Quote from: RichardM on February 07, 2022, 10:04:00 pm
P.S If anyone else in Australia wants to make the same modifications I would be happy to share the PCB costs, I certainly don't need 5 boards

Richard, Yes! I am in Sydney and have 1 x 3468A and 3 x 3478A. I'd like to try this on at least one of them.

Hi Kean, thats great. I am just up the freeway in Newcastle. I would be happy with 2 boards but to be honest we may as well order 5 each and combine postage.

Any ideas on a source for the OLED's ? Aliexpress is mentioned above ?

PM sent.

Richard

Berni · « **Reply #66 on:** February 09, 2022, 06:54:04 am »

Yep burn in is a thing for OLED as the tiny LEDs inside it get worn out and become dimmer

However if you are just displaying static segments the burn-in might be very hard to notice. It's hard to tell if a segment is just slightly dimmer, so in order to see the burnin you typically need to fill up the display with solid lit pixels that way you can see the slight 'shadow' of the burned shape on the area of lit pixels (the difference between fresh new pixels and tired used ones right next to each other). So what the "shifting by 1 to 3 pixels" does is smear out that shadow images edge making it less noticeable in that case.

So id say for your use case OLED burn in is not an concern. It would only become an issue once the burning becomes really really severe to the point where you can notice some segments being dim. Same as what you can see on VFD display test equipment that has had a lot of hours put on it.

mapleLC · « **Reply #67 on:** May 15, 2022, 06:38:44 pm »

Beautiful work.

srb1954 · « **Reply #68 on:** May 15, 2022, 10:13:13 pm »

Quote from: Xyphro on February 04, 2022, 06:44:03 am

The Hp66xx supplies have mechanical same displays, also with 12 digits. Of course supplies like E3632 and similar ones are very different.

Btw. My hp3547 shows when the input is left open in Volt Mode a very huge drifting voltage until I connect it to a source or I change the input impedance to the lower setting. Is this normal or an indication of something dying?

Perfectly normal. It is just the stray leakage currents generating a voltage across the very high (10G $\$\Omega\$$ ) input impedance of the meter. Switching the input impedance to 10M $\$\Omega\$$ is sufficient to drain the stray leakage currents.

ArgyllGargoyle · « **Reply #69 on:** February 01, 2023, 02:55:50 pm »

This looks like a fantastic solution for the stock display - I am probably going to give it a try.
I wonder if there is any EMI impact from the switch-mode DC-DC converters in this design? Has anybody looked at this aspect?

sagias · « **Reply #70 on:** March 09, 2024, 07:07:54 am »

Tested 3478a works ok but i have smpl in place off srq,2w in place of azoff azoff in place of 4w readings are accurate
found 3478a hex icons and 3457a hex are the same compare in hex editor we need the right file

wolfy007 · « **Reply #71 on:** March 10, 2024, 01:28:05 am »

Quote from: RichardM on February 08, 2022, 09:09:35 pm

Quote from: Kean on February 08, 2022, 11:41:45 am
Quote from: RichardM on February 07, 2022, 10:04:00 pm
P.S If anyone else in Australia wants to make the same modifications I would be happy to share the PCB costs, I certainly don't need 5 boards

Richard, Yes! I am in Sydney and have 1 x 3468A and 3 x 3478A. I'd like to try this on at least one of them.

Hi Kean, thats great. I am just up the freeway in Newcastle. I would be happy with 2 boards but to be honest we may as well order 5 each and combine postage.

Any ideas on a source for the OLED's ? Aliexpress is mentioned above ?

PM sent.

Richard

Well if you fellas are going to give it a try, Ill have a go (3x 3478A, 1x3468A & 1x3468B) I have one 3478A going thru repair at the moment I could try it on. Im down Wollongong way.

Kean · « **Reply #72 on:** March 10, 2024, 01:43:27 am »

Quote from: wolfy007 on March 10, 2024, 01:28:05 am

Well if you fellas are going to give it a try, Ill have a go (3x 3478A, 1x3468A & 1x3468B) I have one 3478A going thru repair at the moment I could try it on. Im down Wollongong way.

Hmm, well I forgot all about this and I don't know if I ever ordered any parts. I have acquired another 3478A which arrived with a slightly damaged display, so maybe I should look into this again.

cncjerry · « **Reply #73 on:** March 10, 2024, 03:10:32 am »

I'm using a 3457 more lately and the display sucks in fluorescent light. It looks like the parts used two years ago generally available? I looked at the project and I'm not familiar with the OLED displays. I see they come in 128x32 pixels? I had thought they were just one character, but it looks like that size are all 128x32. But those available are white, and I want blue!

thanks

Jerry

sagias · « **Reply #74 on:** March 10, 2024, 04:52:46 pm »

Fitted neen some trim on pcb and open the right hole a little to align,marks are messy due to wrong fw on github for 3478a,i dont know how to compile hex for 3478a from source, measurements are ok

sagias · « **Reply #75 on:** March 11, 2024, 11:52:56 am »

fw compiled and works flawessly
i provide the filee

cncjerry · « **Reply #76 on:** March 12, 2024, 04:15:39 am »

What oleds did you use?

Kean · « **Reply #77 on:** March 12, 2024, 05:30:05 am »

Quote from: cncjerry on March 12, 2024, 04:15:39 am

What oleds did you use?

The ones linked earlier in the thread are no longer available, but at least the listing with specs and dimension drawing are still there.
I found another listing with similar specs, pin out, and dimensions - but I have not ordered any yet.
https://www.aliexpress.com/item/1005005770683719.html

The price of these is better that the previous listing, but I also saw some even cheaper but from "less reputable" sellers (not necessarily untrustworthy, but just lower reputation).
I will probably order 50 of them in the next couple of days as I want to convert a few meters, and can use these on other projects as well. I guess I need to order the PCBs and other parts too...

sagias · « **Reply #78 on:** March 12, 2024, 05:36:08 am »

As described on xyphros github

sagias · « **Reply #79 on:** March 16, 2024, 11:03:28 am »

Prove

Miti · « **Reply #80 on:** April 02, 2024, 02:51:24 pm »

What about this OLED? Reputable and the visual area seems to be a little wider, it fills the space between digits better.

https://www.buydisplay.com/white-0-87-inch-oled-display-panel-128x32-iic-i2c-ssd1316

Edit: Ignore, the visual area is the same, just different source.

Kean · « **Reply #81 on:** April 07, 2024, 06:25:59 am »

I've just received 20 PCBs and 60 of the previously linked OLEDs [1]. Hopefully in the next week or two I will find time to assemble a sample and check operation.
If any of the Aussie followers of this topic are interested, then feel free to DM me your interest in either bare or partially assembled PCBs.
I may have some OLEDs left over from my builds, but otherwise it is not hard to source them yourselves.

[1] https://www.aliexpress.com/item/1005005770683719.html


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