Products > Test Equipment
Tektronix TDS744 CRT to LCD color converter FPGA module DIY
TerrySt:
Here are the KiCad design files. The socket I am using is the Methode p/n 213044401 through hole. I modified it by milling away the raised areas on the bottom of the socket so that it would sit down further onto the RamDAC chip. I also re-shaped the contacts in the socket to allow them to grip the RamDAC chip better. It seems to work OK after those changes. I never found a socket that worked really well without modifications. The closest one I could find is the Methode p/n 213044601 surface mount socket. It can be made to make contact (with a bit of a struggle), but will pop off a little too easily for my taste. Another socket that can be modified to work is the ASSMAN A-CCS-044-G-T (DigiKey p/n AE10064-ND). It requires less milling of the bottom (just four small posts that can be cut off with a sharp exact-o knife), but the contacts must be removed individually and re-shaped one by one. The design of the Methode through hole socket allows all of the contacts in a row to be shaped at once, which yields more consistent results. I made a small bar out of aluminum that allowed me to bend the contacts around it to get the desired shape.
You also need to source the various cables to connect the board to the o'scope and lcd. No cables came with the lcd I purchased. For the backlight cable, I ordered a DigiKey WM15267-ND. But I had to swap the pins at one end to reverse the order of the pins. The board is laid out for a 1:1 cable, but the cable as supplied by DigiKey reverses the order of the pins.
For the LCD connector, I ordered several from various places on eBay and AliExpress. I was looking for one a little longer than 250mm but could never find one. 250mm works in my o'scope, but not much to spare. I think I ended up using this one: https://www.ebay.com/itm/202290058359, but I'm not sure.
For the connection from the o'scope to the board, I used DigiKey p/n H3CCH-1606G-N. It is a little long, but not too much.
I used a Spartan 7 dev board from Trenz. It was the smallest dev board I could find for a reasonable cost. Others would work (with a new pcb layout of course). The Spartan 7 is much larger than needed. The design I ended up using only uses 49 FFs and 81 LUTs. Just be sure what you choose supports a PLL or MMC module that can provide the 175MHz clock for the lvds interface to the lcd panel. It needs to be phase locked to the 25MHz clock from the o'scope. The CMOD S7 from Digilent would certainly work, but is a little larger. I am already thinking about a new version with an FPGA instead of an FPGA dev board. That might allow me to use the lvds outputs of the FPGA instead of having to use the lvds converter chips.
Terry
TerrySt:
Here is the VHDL code that is based on Vincent's code but with modifications for the serial interface on the V2 version of the LCD panel, and the backlight and reset changes that go with the new design. It works OK, but will occasionally display the wrong colors as settings are changed that affect the palette or overlays. Such as when the colors are changed, or the intensity settings are changed. It works 99% of the time, but occasionally glitches. It is 100% stable when the color, palette or intensity settings aren't being changed.
I was trying to debug the glitches, but I decided to just start over with my own code from scratch so that I understood it better. That version seems to be simpler (to me anyway) and is 100% stable. I'll post it also.
First, the version based on Vincent's code is attached.
Terry
ltarjanyi75:
Hi Terry,
Why can't you use the LVDS of the FPGA with the devboard? Isn't its LVDS outputs available on your devboard?
Btw I am now planning a small board with a Spartan 3. The board will be small (44*41mm) which is ok from the point of fitting on top of the RAMDAC, but I don't know if I will be able to solder it... :)
Thanks,
Laszlo
TerrySt:
And here is the version I created from scratch. This is my first attempt at VHDL coding, so no guarantees. I'm not sure how to attach the automatically generated clock wizard files, so if you need some other files you will have to let me know or just generate them yourself (easy using the clocking wizard in Vivado).
Terry
TerrySt:
--- Quote from: ltarjanyi75 on December 10, 2023, 10:58:28 pm ---Hi Terry,
Why can't you use the LVDS of the FPGA with the devboard? Isn't its LVDS outputs available on your devboard?
Btw I am now planning a small board with a Spartan 3. The board will be small (44*41mm) which is ok from the point of fitting on top of the RAMDAC, but I don't know if I will be able to solder it... :)
Thanks,
Laszlo
--- End quote ---
None of the dev boards that I could find (at least the reasonably priced ones) allow you to set the voltages on the FPGA to the voltage required by the LVDS interface. They all seem to be set to 3.3V, and for LVDS you must set the domain voltage to 2.5V.
I don't know anything about the Spartan 3, but it should be fine as long as it can generate the phase locked 17MHz clock.
Terry
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