Advantest R6581 VFD replacement

[Mickle T.]

As is well known, the Advantest R6581 DMM has two main problems, the second of which is a custom VFD display that is not available commercially.
As a result of reverse engineering the multimeter firmware and analyzing the circuit diagram, I was able to find at least two possible ways to replace the VFD that has become unusable:
1) A difficult to implement, but flexible and interesting way: installing a microcontroller module that "spy" on reading the external dual-port display buffer from the Hitachi H8 controller on the front panel board. The resulting ASCII character codes and their attributes can be rendered on any graphic display.
2) A simple and cheap to implement way: installing a microcontroller module that "spy" on writing to the shift registers on the front panel board of the multimeter. The resulting bit image of characters can be output only to a limited number of displays with a resolution of at least 256x48 pixels.

If you choose the second way (which is what I did), then replacing the display will cost about $20 and half an hour of your time. As a basis, I took the most common STM32 Blue Pill (STM32F103C8T6) and 3.12" OLED with SSD1322 controller. Attached is the schematic diagram and the project archive in STM32CubeIDE.

[TheDefpom]

That is excellent, thank you for providing this !

Now I just need to figure out how to use the STM32 IDE and get a blue pill board and ST-link.

I've never used an STM32 so a bit of STM32 learning is in my near future, which is probably a good thing anyway !

[dietert1]

In another thread a 4.58" TFT bar display was proposed as a possible replacement. In comparison to original VFD it might look like this. Don't know yet how it fits inside the R6581.
The controller uses a STM32H730 and its LTDC peripheral. It fits to the back of the TFT. At 300 MHz the MCU needs about 5 msec to paint the image in its video memory. TFT refresh rate came out as 41 Hz.

Regards, Dieter

[dietert1]

Thanks to Mickle T.s great reengineering it was fairly easy to connect the TFT display to one of our R6581. Also i unmounted the R6581 display board to check available space. The TFT and its controller can become one module and fit very similar to the original VFD.
The firmware reads all display data packets and paints each one of them, so there is no visible delay in comparison to the VFD. I also added kind of OCR to the firmware. Right now it only recognizes that strange "DISPLAY OFF" message and turns the TFT backlight off. Maybe one can substitute the 5x7 matrix by a higher resolution font.

Regards, Dieter

[dietert1]

In order to train the OCR i would like to post various text messages to the R6581 display via GPIB. Many GPIB devices support some kind of message display but i couldn't find the proper GPIB command in the R6581 manual. Who can help with hint?

Regards, Dieter

[Mickle T.]

The original, unmodified firmware does not contain commands for text output and complete blanking of the display.

[dietert1]

Unsoldering the original VFD display was quite some exercise. Meanwhile some brackets (3D printed) were glued to the boards as support for the 4.58" TFT display and its graphics card. A narrow fit!
By the way: The VFD cathodes need about 4 W for heating, while the TFT needs about 20 mA x 12 V = 240 mW for its backlight plus 150 mW for the graphics card. Roughly a 10x reduction.

Regards, Dieter

[dietert1]

First image shows the +12 V backlight supply. It has a voltage doubler and a LM7812.
Meanwhile i finished two R6581T with the replacement TFT display.

The interesting number in the image is the upper one with 15.57 uV. This is with an 18 MOhm resistor and a 1 uF cap across input, so input offset current < 1 pA. That R6581T got a mosfet input mux. The other one got a mains preregulator similar to the Keithley 2002. So there is more work to do..

Regards, Dieter

[kjk24]

Thank you 👍 verry much

[TheDefpom]

Well thanks to Mickle T. I have now replaced my display with a 3.12" OLED, it was always in my plans to do something to replace it, and thankfully I didn't have to sit down for days trying to work it out !

Not sure I went with the best colour, maybe I should have gone with Yellow instead, but it is still a lot better than it was.

I am watching the 4.58" display version with interest (I have a display here already), as that would be even better as then the text would not need to be shortened, would also be nice to use a smoother font for the 5x7, but now I am just being picky LOL.

I have recorded a video of the conversion which I will publish on my channel at some point, I didn't go into detail about the programming of the STM32, as I did that a couple of weeks ago (first time using an STM32), I might have to record something to fill that information gap.

[IanJ]

Hi all,

Just a wee note.......I have an R6581T on it's way, and I think the VFD is ok (famous last words!), but decided to put together one of these OLED solutions anyway. Those that know me will know I like modifying/upgrading my gear!

I have the .HEX file and have uploaded it to one of my BluePill STM32 boards, however, in regards to the toolchain my app of choice is Visual Studio (I don't use Eclipse) for everything including Win apps in VB, Arduino ATMEGA & STM32, so decided to try VisualGDB plugin for Visual Studio (VS 2022) and lo & behold I was able to import Mickle T's source, set up the configuration and compile a .HEX file of my own.

Looking forward to receiving my OLED and trying the original Mickle T HEX file as well as the one compiled by Visual Studio.....see if it works!

Anyone else tried this?.......so far VS VisualGDB plugin is looking workable!

UPDATE:
No R6581T yet so scoped the STM32 pins with original HEX, got some waveforms, then uploaded my own HEX file from VS and scoping them again I get exact same waveforms, so looking good.
Original HEX file = 29.6KB
VS HEX file = 39.9KB, so I can only assume VS debugging overheads & optimization.
I haven't started looking at Mickle T's source code at all, but looking forward to having a look around, and knowing me tweaking.

UPDATE:
The VS2022 compiled project does work with the R6581T & OLED.

Ian.

[TheDefpom]

Here is my video about replacing the display on my unit:

[IanJ]

Hi all,

Below is a link to my conversion of Mickle T's original source project to a Visual Studio project (Windows).
It compiles to a hex file just fine..........Untested though, although the uploaded HEX file does seem to scope the same signals on the STM32 board.
No source changes were necessary at all.

VS2022 64-bit, Community Edition
Requires VisualGDB plugin for VS (30-day demo version will do) - https://visualgdb.com

https://github.com/Ian-Johnston/OLED_SSD1322_DMA

Ian.

[dietert1]

Here is a zip archive with that H730 LTDC TFT replacement display project. As i have some ready to use PCBs left i thought about making them into kits, but i don't have time to support that.

Regards, Dieter

[IanJ]

Here's my OLED conversion photos below.
And my YT video: https://youtu.be/QyP6tK9EIsg

I also modified the OLED display (SSD1322 iREF pin) to increase the brightness just a touch to compensate for the smoked perspex. Instructions are in the video.

A big thanks to Mickle T......what a difference this has made to my R6581T.

Ian.

[IanJ]

Here is a zip archive with that H730 LTDC TFT replacement display project. As i have some ready to use PCBs left i thought about making them into kits, but i don't have time to support that.

Regards, Dieter

Hi,

Any chance you can export the gerbers?
Looks like and older Eagle binary .brd file which Kicad etc can't open.
Thanks,
Ian.

[dietert1]

Yes, it's Eagle version 4.16. Can't you just order the PCB using the board file? I never had to supply Gerber files. The PCB is four layers, size 65 x 40 mm.
In case somebody wants to design his own PCB i added a schematic. R7 .. R12 are three voltage dividers for the 5V logic data inputs. Later i checked that those STM32H730 pins are 5 V tolerant and omitted R10 .. R12.

Regards, Dieter

[branadic]

Hi,

Any chance you can export the gerbers?
Looks like and older Eagle binary .brd file which Kicad etc can't open.
Thanks,
Ian.

Workflow is easy, open it with Eagle 7 Lite, save it and you can import it to KiCAD. Attached is the Eagle 7 board file.

-branadic-

[IanJ]

Hi all,

So far so good, a day spent on Visual Studio and I have mapped the incoming bitmap data to ASCII characters, getting ready for driving a TFT display.

Screenshot attached, a live debug session in VS with the STM32 and that's "+ 1.2345638    VDC" appearing in the code (G1 to G18) from the R6581T.

Next, I'll deal with the AUX display G19 to G47, and the annunciators after that.
From there get a LT7680 TFT driver loaded and start send data to the new display and playing with fonts etc.

Again, completely impossible without MickleT's great work on the original reverse engineering.

PS. C is pretty new to me albeit I've done loads of C++, so it's not too far away.

Ian.