HP3548 / HP3457 OLED display

[kawal]

Added a drawing to illustrate the issue of ear overlap.

[kawal]

instead of cutout there could be just drilled holes.  There are extra long headers .

[kawal]

This is the shape i propose to make the PCB

[TERRA Operative]

Good stuff, I'll take a look this week and make the changes.

[kawal]

Good stuff, I'll take a look this week and make the changes.

If you have KiCAD  version  of your board I can do the modifications.

[TERRA Operative]

Only Diptrace unfortunately.
I have yet to figure out how to use KiCad for more than 30 minutes without rage quitting... Open-source syndrome with the UI and all....

[kawal]

Looks like diptrace available as freeware up to 500 pins.  Could you  send the schematic and design  files?  I will see if there are export options or just use diptrace to modify .

[TERRA Operative]

Here you go.

(Latest version further down this thread).

[kawal]

This is what i was thinking

[kawal]

I don't know whats up with Diptrace, but not happy. Again the footprint is wrong for U3. The footprint is too big for SC-70 and too small for Sot-23.  The Sto23-5 used is not standard size of 0.95mm pitch but 0.65mm pitch.  Not sure what that even is.  .......


OK  figured it out SOT-23-5 0.65mm pitch is SC-70-5  OMG!!! 

[TERRA Operative]

Ok, I've made another revision with the clearances made for adjacent screens.
I also measured up one of my 3478A multimeters and adjusted the board outline and mounting hole positions to be more accurate.
And finally, I tweaked a few things and have updated the BOM file etc to use more of JLCPCB's basic parts to try to reduce cost and make assembly easier.


I'm getting a quote on a run of 20, 10 of which will be spare, so in a while I might have a bunch for anyone who wants some. But no promises how long away...

[TERRA Operative]

So I finally got a batch of PCB's made and the first one I hooked up works. (Soldering the OLED's was a slight pain, took a few passes with the soldering iron to get them all reliably working. I need to design an alignment jig...)
I had to figure out the fuses thing (I am completely NOT a software person... ) but it seems to be working well, besides a few things detailed below.

When I turn the instrument on, instead of 'SELF TEST OK' showing, I get 'P@@@ P@PP @@', then it all works ok as expected when showing the readings. If I have the programmer plugged in (supplying 3.3V directly to the MCU) then SELF TEST OK appears as expected. So I think this is a power supply thing, maybe the 3.3V rail takes too long to come up? Or I have a fuse setting to change?

I have the following fuses set in Microchip Studio:
HIGH.SPIEN
HIGH.BOOTSZ -> Boot Flash size=256 words Boot address=$0E00

LOW.BODLEVEL -> 2.7V
LOW.BODEN
LOW.SUT_CKSEL -> Int. RC Osc. 8MHz; Start-up time: 6CK + 0 ms


Also, even though I used the 3478A .hex file, the annunciators are wrong. It appears that the three different files uploaded by Xyphro are identical, not three different versions...
I found sagias had the same problem but they provided a .hex which has the correct annunciators. Thanks!
How do we go about making our own annunciators? I see the python script etc, but is there any instructions anywhere? I wouldn't mind making some more firmware files with different annunciators for other instruments too.


And finally, when performing a self test, the annunciators don't appear as they do on the original LCD (to check all segments work on the LCD), if this worked it would help identify what firmware the MCU contains. Is this difficult to implement?



Anyway, here are some pics of it in one of my 3478A multimeters.
I had to make some last minute manual changes with a nibbling tool to one of the PCB's to fit this model. This 3478A is the type with individual removable panels instead of one single outer case, and needed just a bit of a trim to fit.
The latest files with the mods are attached below too. It should fit everything else still.


I have a few ideas for further improvements, mainly to manufacturability, and I want to try to fix that garbled display on power-up if possible, so stay tuned for another revision some time soon-ish.

[wkb]

OMG.. now you are tempting me to convert at least one, if not both of my 3478A.

As if I need more projects 

[porter]

Beautiful job.
I have a bit of affection for my 3478A.
One of the nice things about it is the 30mv range. If my math is any good, it gets close to 6 1/2 digit accuracy of some meters with 200 mv ranges.
For example if I want to measure  10mv, the Siglent 3065x has 5uv accuracy (1 year specs). The 3478A for the same measurement has 7.5uv accuracy (1 year spec). Plus it has the famous LM399. Not bad for the oldie.
 

[TERRA Operative]

So, I've been playing around a bit, trying to iron out that 'SELF TEST OK' not showing correctly on boot.

I thought maybe the MCU needed more time to settle down so I added a 4.7uf capacitor in parallel with C763 on the meter's main board (located just near where the transformer wires are soldered to the board) to increase the power-on-reset time of the multimeter.
That took the reset time from about 11ms up to around 128ms, but still I get the garbled display.

I'm thinking that maybe the MCU doesn't sync properly until it receives a message or two?
Anyone good with firmware? I'm not... 


Here's a quick video of what it does on boot:
https://youtu.be/hfPargPhheM

[robert.rozee]

just an observation, and i don't have one of these meters, is that using 13 displays would have enabled the use of a dedicated display for the decimal point and made for a far easier to read result. the down side (assuming 13 of these displays would even fit) is that shuffling digits around the decimal point would have added an extra layer of complexity.


cheers,
rob   :-)

[porter]

So, I've been playing around a bit, trying to iron out that 'SELF TEST OK' not showing correctly on boot.

I thought maybe the MCU needed more time to settle down so I added a 4.7uf capacitor in parallel with C763 on the meter's main board (located just near where the transformer wires are soldered to the board) to increase the power-on-reset time of the multimeter.
That took the reset time from about 11ms up to around 128ms, but still I get the garbled display.

I'm thinking that maybe the MCU doesn't sync properly until it receives a message or two?
Anyone good with firmware? I'm not... 


Here's a quick video of what it does on boot:
https://youtu.be/hfPargPhheM

Is this section relevant? (maybe not since you mention the 3.3v supply)

 

[Miti]

Hmm, this caught my attention. I have two HP3478A and even though there’s nothing wrong with their displays, this project looks really good.
Regarding the SELF TEST OK not showing up, did you try to do a hard reset on the instrument (short C763) after it start showing the reading? If the self test shows up, that means the board needs more time, if it doesn't, well, needs more digging. Or try the soft reset, SHIFT + RESET.
Also disable BOD and see what happens.
I’m thinking of making a single board with 3D bracket, as an improvement.

Cheers,
Miti

Edit: Edited my first post for clarity.

[Miti]

I looked through the code a bit. It takes the display 500ms+ to initialize. There are three 100ms delays and a 200ms one. I think that’s your problem. I’m not sure if it needs that much time but in my opinion they are excessive. You can try recompile the code with something like 10-20ms delays.

Cheers,
Miti

[TERRA Operative]

I played around with some things and now it's working! Thanks for the pointer!

Attached is the working hex files for both the 3478A and 3457A.


Last thing to make it all 100% as per original, is to get the annunciators to show when manually performing a self test.
I'll poke at things later. I'm slooowwwlllyy learning this firmware stuff...

[Miti]

What did you play with, the delays?

[TERRA Operative]

I think I didn't need to.... Somehow when I recompiled the .hex, even with the original delay times it just 'started working'. Not sure why, but maybe I accidentally fixed something that I somehow broke as I have no idea how to use the Atmel Studio software....

[TERRA Operative]

Anyone smarter than me able to tell me how to make all pixels on all the displays set to 'on', and also all the numeric 'segments' and all annunciators set to on too?
I just want to have a .hex file for each mode so I can turn on power and it just constantly displays regardless of data input.

I want to measure current draw of the OLED displays... But I'm not very good with firmware....   


I'm 99% to the point of completing my design. Just a few small details to make it perfect.

[Kean]

Anyone smarter than me able to tell me how to make all pixels on all the displays set to 'on', and also all the numeric 'segments' and all annunciators set to on too?

On a 3478A if you initiate a self test via blue then SGL TRIG buttons, the full display should come on for as long as you hold SGL TRIG.
This won't be all OLED pixels, only those associated with numeric segments and annunciators - but that should be worst case for normal firmware operation.

[TERRA Operative]

Yeah, this is what I want to ultimately measure the current draw of, but when doing the self test, the OLED firmware doesn't seem to show the annunciators.