Electronics > Repair

Advantest R6581 VFD replacement

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IanJ:

--- Quote from: gamalot on December 01, 2024, 10:33:16 am ---I tried to capture the dot pattern of all characters, but I only got 80 of them. There are a few characters that I have not been able to display on the screen, such as lowercase letters b, j, p, q, and left and right brackets.
I attached the characters I found, each character takes 6 bytes, the first 5 are captured from the serial bus, and the last byte is the ascii value.
I also tried to use different fonts to present them, maybe because of my lack of artistic cultivation, I am not satisfied with my work so far ...

--- End quote ---

Thanks, I know there are some characters I haven't mapped properly yet, certainly some of the alphabet, and those up/down arrows etc. MickleT also mentioned some special graphics under one of the menu's.
Not sure if they and some others are available in the LT7680A-R character map sets, if not I'll have to create a few UDG's. The LT7680A-R has a flash rom on it that's available to upload to.

A couple of limitations, one being there is a maximum font size of 32x32 in the LT7680A-R internal set, but it does allow a x2 to x4 multiplier on top of that for the size. Their way of reducing character map memory footprint I guess.
So, I am using 16x32 with a x3 multiplier, you can see the jaggies on some of my characters.....................The pitfalls of such a hi-res LCD!

Pic below of my progress today, live data now working. Hmmmm, wonder if it's worth putting the AUX line in a different colour!

EDIT: Added another couple pics with Annunciators and different colours, taking my Keysight 34461A for some ideas. Green behind the R6581T panel looks too dim I think.

This has been great fun so far......especially as I am no software engineer!

Notes:
TFT LCD Display refresh rate = 14.5Hz
Used FLASH: 25KB out of 64KB (39%)
Used SRAM: 3544 bytes out of 20KB (17%)

Ian.

dietert1:
That looks nice, so higher resolution fonts may be worth it. I also went to white as the R6581 front bezel takes away quite some brightness and i wanted to stay with 20 mA backlight current.
I also thought about using color, e.g. show the error anunciator or other error info in red.
Or if the meter operates in the same range for some time, one could replace the range info by a running average including standard deviation. A real playground..

Regards, Dieter

IanJ:
All,

For some reason I found yellow has more punch through the R6581 bezel than white, not a lot in it mind you and maybe just my eyes.

The OHMS symbol is testing me to the limit of my C coding ability.......
The LT7680A-R only supports ISO 8859-1, 2, 4 & 5....and not an OHMS symbol in sight.

It does support UCG - User defined Characted Sets - but the datasheet/manual/App note is pretty sketch in it's usage.
I think I have my hex array stored properly, but calling it up for display brings up a blank.
I swear it was a lot easier to do on the ZX Spectrum back in the day!

I have a contact at Levetop Semiconductor, waiting on a reply, and hopefully some sample code.
They have been great, offering assistance!

It'll be nice to get the UCGs working, it will help with the E0 to E8 extended chars required for the DIAG screen vertical and horizontal fills.

EDIT: Levetop sent me sample code for UCG’s…….great stuff!

Ian.

IanJ:
Hi all,

Managed to get the UCG user-defined characters working on the LT7680A-R IC per the attached.

Small issue with the smaller one, so had to swap it out for the word 'ohm'......for now anyways.
I can create any amount of UCGs and call them up as long as they are all the same size.......but defining 16x32 and 12x24 has proved problematic due to the way the LT7680A-R works.......as I see it.

Another small issue is the line right along the bottom of the LCD (which actually won't show up behind the bezel), I can get rid of it by adjusting the display parameters, but it tends to make the display unstable in other ways.....so leaving it as it is. If I had access to the FULL spec of the TFT LCD then I could probably fix it but alas no full spec!

UPDATE:
I fixed the 2nd OHM symbol on the AUX line. Suggestion from Levetop, instead of rendering the UCGs at boot and using them individually, I am now rendering them on the fly just before they get used in the same area of memory. A little bit more of a CPU overhead for the Blue Pill but it seemed to handle it ok and the display is still fast.

Ian.

IanJ:
Hi all,

Enough software for now, all working including ohms symbol.

Info:
Lcd update rate in every mode except resistance = 20.4Hz.
Lcd update rate in resistance modes = 14Hz.
This is due to the on-the-fly uploading of the user defined ohms graphic (hex symbol data) to the LT7680A-R IC.

I have also been working on a Pcb that will mount on the back of the display board and hold the LT7680A-R and Blue Pill board, keeping everything as low profile as possible.
Resultant connections to be made are just the 5 wires to the R6581 display board to pick up +5Vdc and the 3 serial signals.

Photos attached.

EDIT:
Re-mounted on back of display board (more room), much better mounting.

EDIT2:
Found issue with backlighting registers so have managed to increase brightness by about 10%+ over the photos below.

EDIT3:
My GitHub repo for this project:
https://github.com/Ian-Johnston/R6581_VS_Display

EDIT4:
I have edited the character encoding on the ones I had missed on the DIAG screen, and have come up with my own idea for the animated DISPLAY test. That should now cover everything and thus no longer displaying "?" for any missing font data.
Also added an option to tie input pin B0 down to 0V to swap the colours on the MAIN and AUX lines at boot. Default white for MAIN and yellow for AUX.
https://youtube.com/shorts/ayPeOh1u92w?feature=share

Ian.

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