Replacement display for Datron 1271/1281 and possibly for 4950/4920 as well - Page 1
Forum section: electronics / repair

author: picburner
author_rank: Frequent Contributor
timestamp: February 13, 2021, 05:15:45 pm
content: Some time ago I bought a working Datron 1271 multimeter, but as has happened other times, the shipment was not painless: the right VFD display arrived damaged.The packaging had been done well enough but the instrument had two very thin adapters on the sides of the front for rack mounting.The blows received during the transport concentrated on these adapters and broke the little glass tube that was used to create the vacuum in the VFD.This display is essential for some operations, so I first looked for a spare but soon I realized that it is practically unobtainable.So I tried, through the signals generated by the instrument, to convert the bits dedicated to the switching on of the individual pixels of the original display into characters and symbols to be sent to an LCD or better an OLED.After a few unsuccessful attempts I finally succeeded in using a "Bluepill" as a development board and writing a dedicated program in 'C'.The photos show some menus of the instrument with a 4002OLED display but an LCD can also be used.I also made the final pcb but I'm still waiting for it to be delivered to me (I finished it just in time for the start of CNY ....).If someone else is in the same condition as me I can give the gerbers, the schematics and the code, but first I have to wait for my pcb and check that the front cover of the instrument closes without problems...

author: doktor pyta
author_rank: Frequent Contributor
timestamp: February 13, 2021, 10:17:22 pm
content: picburner,display substitutes certainly deserves a place hereP.S. I didn't knew that finding suitable 1x40 VFD occurs to be such problem.

author: coromonadalix
author_rank: Super Contributor
timestamp: February 14, 2021, 01:21:31 am
content: Good job

author: guenthert
author_rank: Frequent Contributor
timestamp: February 14, 2021, 03:31:11 am
content: Hmmh, while it's a job well done, it's a pity that you lost the original VFD. It's emerald and by far the most beautiful display of all my DMMs.

author: TheSteve
author_rank: Unknown
timestamp: February 14, 2021, 04:56:53 am
content: Awesome work! The vacuum port is hanging out in such a dangerous place. I've operated my 4920M during repair with the front plastics removed and that thing has "break me" written all over it. Please do share everything you've created as others will certainly benefit from it.Maybe we can get a matching left side display made too at some point.The original VFD's are very nice, and a rather unique color it seems.

author: picburner
author_rank: Frequent Contributor
timestamp: February 14, 2021, 05:54:40 am
content: @ doktor pyta:The original display is an Itron DC405E2 and due to how the dot matrix is organized makes it difficult to replace with other VFDs.

author: picburner
author_rank: Frequent Contributor
timestamp: February 14, 2021, 05:56:46 am
content: @ guenthert:I would have preferred the original display too but unfortunately I have no other choice.However, the color of this 4002Oled is a little closer.

author: picburner
author_rank: Frequent Contributor
timestamp: February 14, 2021, 05:58:22 am
content: @ TheSteve:Emulating the left side display is perhaps even easier using a graphical display and the stm32f103c8t6 has enough power to drive both.At that point, however, it would be convenient to replace all the original pcb with a new one.Yes, the two vacum ports are very very too close!

author: MadTux
author_rank: Frequent Contributor
timestamp: February 17, 2021, 12:08:19 am
content: If it fits, I'd simply rewire such a display with thin enamel wirehttps://www.ebay.com/itm/Noritake-CU406ECPB-U2A-vacuum-VFD-display-/392966929744

author: picburner
author_rank: Frequent Contributor
timestamp: February 17, 2021, 05:43:47 am
content: Thanks for the warning but I have ascertained that the glass is longer: about 220mm against about 182mm of the original.But the biggest problem is the different organization of the pixel matrix (in the original VFD the anodes of the first 20 characters are separated from the following 20 characters, in the newer VFDs are not) which would oblige me to modify the electronics too.But at that point....

author: picburner
author_rank: Frequent Contributor
timestamp: February 17, 2021, 08:58:19 am
content: To highlight the problem mentioned in the previous post here is the solution adopted by a bbs.38hot.net forum user: he had to use two separate 20x2 VFDs.In doing so, however, an empty hole remains in the center between the characters.

author: coromonadalix
author_rank: Super Contributor
timestamp: February 17, 2021, 12:00:32 pm
content: If picburner solution works for him goood other will do their own implementation, even i could not do better, i'm good in electronics, do rewiring etc ... but i'm bad at any coding or protocol sniffingI helped quick1 complete his oled variant for the 34401a display, he was missing some data signal / timings etc ... and i had problems to make an cheap stm32 work at first lolllThe graphical display advantage, its already wired and have the drivers on it, just need the stm32 as an interpreterI think someone remade an complete front pcb for a datron calibrator and added more modern displayMaybe the @Madtux Ebay display could work or fit if the vfd section is pulled out and retrofitted on a new board ??Some vfd's have began to be discontinued on some sites ....

author: picburner
author_rank: Frequent Contributor
timestamp: March 03, 2021, 01:14:25 pm
content: Finally I have completed my project and, as anticipated, I publish the necessary files for the realization of the right display replica for the Datron 1271/1281.As you can see from the images, using a blue OLED, you hardly notice the difference in tint between the original VFD display and the replacement one.I had to do some small tweaks to the pcb, things you notice when you do the final assembly, so I was right not to post the files immediately.You need two 5mm spacers (with 3 mm hole) between the original pcb and the new one and four 5mm spacers (with 3 mm hole) between the new pcb and the OLED panel.The connections to be made are specified in the schematic.To program the micro stm32F103 you need an ST-Link v2.A forum user asked me in PM if it was possible to make a left display replica also: this is possible but I think it will take some time, at the moment I am a bit busy in other projects.Note: The gerbers are made with JLCPCB rules.

author: picburner
author_rank: Frequent Contributor
timestamp: March 03, 2021, 01:29:49 pm
content: Ah, I forgot to add a pic of the pcb which, due to some modifications, now it can be considered another prototype (but for me it remains definitive).The pcb dimension is 184x36mm.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 03, 2021, 03:17:15 pm
content: looks like it was made like this

author: doktor pyta
author_rank: Frequent Contributor
timestamp: March 03, 2021, 03:55:54 pm
content: beautiful

author: TheSteve
author_rank: Unknown
timestamp: March 04, 2021, 05:24:21 am
content: Looks amazing! Thank you for sharing the design. I don't need it today, but tomorrow you just never know. The lab will always welcome more Datron equipment.

author: chinapp
author_rank: Contributor
timestamp: March 13, 2021, 05:25:36 am
content: waiting for the left display project

author: pelule
author_rank: Frequent Contributor
timestamp: March 13, 2021, 09:33:26 pm
content: Grate job, hope to see more

author: picburner
author_rank: Frequent Contributor
timestamp: March 19, 2021, 02:53:43 pm
content: For all those who are asking me here and in PM when the project of the other display will be ready:I can devote only a little of my free time to this undertaking, so it will take several months, be patients.

author: jfriend
author_rank: Contributor
timestamp: May 22, 2023, 01:57:14 pm
content: What was the P/N of the oLED display you used that had a very similar color to the original VFD?

author: picburner
author_rank: Frequent Contributor
timestamp: May 25, 2023, 01:21:27 pm
content: I bought it on Aliexpress some time ago. The shop isthisIn the description it says: SOC4002A.Of course you have to choose the blue one.

author: rigrunner
author_rank: Frequent Contributor
timestamp: May 26, 2023, 05:07:08 pm
content: That looks great. Well done

author: jfriend
author_rank: Contributor
timestamp: July 20, 2023, 10:35:51 pm
content: I had a board made using the gerbers you provided and populated it according to the schematic. I successfully loaded the hex into the STM32. However, nothing happens when I connect the board to the VFD board. I've triple checked all the connections, they are correct. Turing my attention to the build, I don't read any crystal oscillation when using a 10:1 oscilloscope probe. My question is, is the hex up-to-date and has anyone else built one of these successfully? I'm not sure what else to test or check.I noticed on your board photo R4 and R13 are not installed.

author: picburner
author_rank: Frequent Contributor
timestamp: July 21, 2023, 03:26:10 am
content: R4 and R13 are only needed if you're using an LCD display (Look at the schematic).Crystal Y2 must oscillate at 8MHz otherwise U4 cannot work.Y1 was needed for an unimplemented function instead, you can also not mount it.Check the soldering of the U4 pins very well and that there are no jumpers between one pin and the adjacent ones with a microscope or a very powerful lens.

author: jfriend
author_rank: Contributor
timestamp: August 09, 2023, 11:12:18 pm
content: I still haven't had success getting the circuit to run. I finally found time to start over and build another one but it has the same result; it doesn't run. In my experience with other microcontrollers (mostly Microchip), you have to specify the clock source at some point either when writing or compiling the code. I just wondered if you had done this or if there's a parameter I need to set when programming from Cube.

author: picburner
author_rank: Frequent Contributor
timestamp: August 10, 2023, 06:31:33 am
content: The micro clock configuration is already in the supplied HEX file. The internal clock is 72MHz obtained by activating the internal PLL.You have to upload the file via STM32CubeProg & ST-Link/V2 only.However, as previously said, if there is no 8MHz on pin 6 of U4 (STM32F103C8T6) the circuit will never work.The processor must be an original STM32F103C8T6, there are currently clones such as the CS32F103C8T6, STM32FEBKC6 and CH32F103C8T6 which I have not tested and cannot guarantee that they will work without software changes.Take some pictures (detailed) of your pcb (front and back) maybe I can see something you missed.

author: jfriend
author_rank: Contributor
timestamp: August 10, 2023, 01:36:34 pm
content: So it's an STM32F103C8T6? The schematic shows STM32F100C8T6B, which is exactly what I purchased. Maybe that's the whole problem. I'll get a 103 and try it. And yes, I am using genuine ST parts and Cube programmer with a genuine ST-LINK/V2, not a clone. If that doesn't work, I'll take some clear board photos for you to examine. Thanks so much for your attention and help!

author: picburner
author_rank: Frequent Contributor
timestamp: August 10, 2023, 05:20:56 pm
content: Sorry, a while ago I fixed the error in my schematic and in my pdf but I forgot to replace the schematic in pdf format into the zip archive.Now, albeit a little late, I did.The reason for the failure is obviously that.

author: DavidAlfa
author_rank: Super Contributor
timestamp: August 10, 2023, 05:31:52 pm
content: Make the binary limited to 64KB / 8KB and 24MHz, then it will compatible with any stm32F10x C8/CB.If you limit it even more to 16KB/4KB (Shouldn't be too hard unless you use HAL) then it will also work with C6 and C4 devices.Your binary only uses 12.7KB, so only needs tweaking the cpu speed and ram block in the Linker Script.Also, is the external oscillator actually required?

author: picburner
author_rank: Frequent Contributor
timestamp: August 10, 2023, 06:34:40 pm
content: QuoteThe internal oscillator could probably suffice. I'd have to do some testing to be sure though. But since it's a one-of-a-kind piece and not a mass production, I might as well waste a quartz.

author: jfriend
author_rank: Contributor
timestamp: August 13, 2023, 01:50:34 am
content: I got it to work the first time with an STM32F103C8 processor. That was definitely the problem. Now I've got another small issue, a couple characters randomly appear as inverted question marks (¿). I haven't gone past the first warm-up screen to see if it still shows up. Photo attached.

author: picburner
author_rank: Frequent Contributor
timestamp: August 13, 2023, 03:06:16 am
content: What Wavetek model is it? I tried it on a 1271.The inverted question mark means it doesn't recognize a character pattern.Strange that it is the "T" character that is in the table.What is the other character?

author: picburner
author_rank: Frequent Contributor
timestamp: August 13, 2023, 04:02:47 am
content: But I see that in the previous word the "T" is there, so it's not a pattern failure problem and moreover the problem is randomly.Isn't that the cables between the Wavetek and the pcb/display assembly are a bit long?

author: jfriend
author_rank: Contributor
timestamp: August 13, 2023, 01:46:42 pm
content: After a little more testing, I see it is the 21st character position on the first row that does it most. The first position does it once in a while, and the 3rd or 4th (don't remember which) does it rarely. It does not matter if there is a character there, it will do it even when the position is blank.

author: jfriend
author_rank: Contributor
timestamp: August 14, 2023, 05:15:03 pm
content: To answer the previous question, this is a Wavetek 4950.

author: jfriend
author_rank: Contributor
timestamp: September 01, 2023, 10:09:31 pm
content: I ordered a second OLED just in case it was the module itself. Installed it, no change. It is doing exactly the same thing, although it seems to be favoring the first position on the first row rather than the 21st character. The cable length is 12" to connect to the back of the Wavetek display and wrap around the front to the connector. The wires are all the same length. If that were an issue, I would expect a lot more trouble with random characters, not the consistency I'm observing.

author: picburner
author_rank: Frequent Contributor
timestamp: September 02, 2023, 05:54:58 am
content: The problem you described wasn't the OLED, so replacing it wouldn't have changed anything.The cable should be fine I was able to make it an inch shorter only, so that's not the problem.I don't know if you have the service manual of your Wavetek 4950 and you happened to study how the image on the two displays is built starting from the serial data stream.However, on the display located on the right, the raster is built by sending the first and twenty-first character, then the second and twenty-second, then the third and twenty-third and so on. So if for some reason there is a timing problem the 1st and 21st characters can be misread and show uncertainty (As it happens now).Adding an unexpected device (the new display circuit) may affect the stability of the existing system.I initially had this problem myself and fixed it with a software delay.Unfortunately now I can no longer access the computer and the compiler that I used at the time to create the code and I can no longer make changes.The only thing you can do is introduce/modify a hardware delay on the data line of the signal (a capacitor, C6 1nF*, already exists on the Data-IN line). Try decreasing or increasing it.* on the original Datron/Wavetek Display Board.

author: jfriend
author_rank: Contributor
timestamp: October 02, 2023, 09:49:10 pm
content: Update on the 4950 compatibility... the design offered in this thread doesn't appear to be fully compatible with the 4950. Nothing so far has worked to clear up the inverted question mark ¿ character, and the display test fails to sequence blocks left-to-right as a button is pressed. As-is, this design probably isn't going to work with the 4950 (can't answer for the 4920 but I suspect it will be the same).What I have tried:- Started over with a new blank board and new components (again).- Installed only required components for OLED as indicated by the OP and schematic.- Experimented with various capacitors as suggested to skew the data line timing slightly.- A different OLED module.- Resoldered the wires from the 4950 to the converter.Because itpartiallyworks, it doesn't appear to be a wiring or display module problem but rather the microcontroller program or timing.

author: picburner
author_rank: Frequent Contributor
timestamp: October 03, 2023, 05:43:58 am
content: In fact, in the title I wrote: "and possibly for 4950/4920" because, unfortunately not having a 4950 and/or a 4920, I was unable to test them.The display schematic is almost the same for all four instruments but Wavetek may have changed something in the firmware regarding the timings.The fact that the problem is always on the first and twenty-first characters indicates that there is a synchronization problem.You can try to slightly modify, in more or less, the value "17" indicated by the red circle in the image of the HEX file of the code.Naturally you have to recalculate the checksum of the row according to the change.That value modifies the timing of the synchronism.

author: jfriend
author_rank: Contributor
timestamp: October 03, 2023, 01:48:29 pm
content: Correct, I knew this wasn't a guaranteed solution for the 4950.Location 0x100D90 in the updated HEX you posted (that worked with the STM32F103C8) is nowhere near the same as your screenshot.

author: picburner
author_rank: Frequent Contributor
timestamp: October 03, 2023, 05:10:41 pm
content: Yes, my bad. I got a file that does another job.I downloaded the hex file directly from msg#3492190 to be safe.The string to search for is "2F07C0F200" and the number to change is "2F"

author: View[+]Finder
author_rank: Unknown
timestamp: January 25, 2025, 08:05:27 pm
content: Yes, this thread has not had much posting in the last four months. There are not a lot of Datron meters in use and building displays from scratch takes time. I have displays from AliExpress and boards from PCLPCB ready to build. Meanwhile, i need to use the 1271 "as is".Soooo, back to basics with @picburner initial post.To use the info display while fixing other issues, my plan is to use a pre-built board and the AliExpress display.Seephotos below.NOTE: my vision is not good enough to solder tiny components.

author: View[+]Finder
author_rank: Unknown
timestamp: January 29, 2025, 08:37:17 pm
content: Attached is documentation for the OLED display. Wish me luck, it is supposed to work with Arduino . . .

author: picburner
author_rank: Frequent Contributor
timestamp: January 31, 2025, 05:03:02 am
content: I am answering here to the question posed in (https://www.eevblog.com/forum/metrology/datron-1271-replacement-right-side-display/) since it is more related to repair than to metrological issues.The connections I used are shown in the schematic (the pdf file contained in the zip archive, Reply #12 on: March 03, 2021) and are exactly those shown on the display pcb silkscreen as per the attached images."F1 and F2" are the connection to the VFD display filaments.Since I put a switch to turn off the displays in case of prolonged operation of the instrument via gpib, this connections allows you to turn off the oled display also.Edit: P1 is the connector used to program the STM32 micro. I use a special clamp that connects to the programmer ST-Link V2.

author: View[+]Finder
author_rank: Unknown
timestamp: January 31, 2025, 11:32:45 pm
content: PCB layout for text output attached. Shows connections for SCK1 MOSI1 PA11 VCC and GNDPhoto is of my probe of signals:CH1 is SCK1CH2 is MOSI 1no data on PA11MY PLAN is to try "@picburner 1.0" and use an Arduino or Blue Bird STM32 to see if text data can be extracted to the 4002 OLED. The DT1271 output is serial and the OLED is 4-bit parallel, so there is probably something online already, not necessarily for Datron. Now back to the documentation.If this problem has been solved already, send link.p.s. I have been through the schematics for both 1271 and 1281 and have not found the PCBLayout provided by @Picburner. If that was done by hand, many thanks !!!

author: silly sausage
author_rank: Regular Contributor
timestamp: February 01, 2025, 08:22:03 am
content: looks just like a brough one!

author: picburner
author_rank: Frequent Contributor
timestamp: February 01, 2025, 09:35:48 am
content: @"View+Finder"I can give you a little help since I found a my note on the data to convert to text based on the VFD display bit firing map taken from the serial stream.This data, once you understand how it all works, should make your job easier.All I managed to recover is this and I can't help you further, sorry.Others have recently done similar work,hereandhere, for another DMM, the Advantest R6581, but the display they use is graphical, not character.

author: View[+]Finder
author_rank: Unknown
timestamp: February 01, 2025, 05:04:19 pm
content: @picburner Thanks for the bit pattern--that will make the task easier for sure.As I mentioned in an earlier post, my short term goal is the replicate @picburner's initial Blue pill version--just to get the 1271 working. If anyone has the original code in C, that would move my repair along faster. Otherwise, I can load the hex file into the Blue Pill and see what happens. Yes, I have the OLED documentation and five of @picburner's design PCB's for use down the road.Am I correct that the SCK1 and MOSI1 signals comprise the character data stream that could be translated by the bit pattern?At present I am using paper cutouts of what the right side display should show for various operations. Also using GPIB to take measurements and control the 1271.Oh, and FYI: the broken right display is available if anyone wants it. It was cut from the board, not desoldered.