2
\$\begingroup\$

I just scavenged an TFT display from a digital picture frame. Using the number on the back of the panel, I was able to locate and download the data sheet.

The Picture frame panel The number and manufacturer of the display I read through the document hoping to drive it using rows and columns using a Microcontroller, but I am stumped by the terminology and concepts,

Other online and offline resources all discuss how to drive the display using a specialized, dedicated interface chip. Are there any resources that discuss how a TFT works and how to interface with it at the "glass root level"? I am assuming they all operate similarly and have similar hardware interfaces.

\$\endgroup\$
3
  • \$\begingroup\$ You will need that specialized, dedicated interface chip. If you can find its part number and use it, that is the only way you will get that TFT to work. You do not know how to interface to the existing board? \$\endgroup\$
    – user105652
    May 22, 2016 at 21:37
  • \$\begingroup\$ Before you waste any more time, no, it's not possible to drive a raw TFT display with a microcontroller, it is far far too slow. \$\endgroup\$ May 22, 2016 at 22:52
  • 1
    \$\begingroup\$ @TomCarpenter - that's not really correct. There are many, many micros that could probably get an image on this, it's more a question of how complicated an image, something with a synchronous serial interface engine that can be kept full (no dead time between words) could do quite well. And unlike CRTs, many LCDs tolerate being underclocked well below their stated timings. \$\endgroup\$ May 22, 2016 at 23:02

1 Answer 1

1
\$\begingroup\$

That's one of the odder LCD interfaces I've seen, but it doesn't seem like the uniqueness would be a complete show stopper.

While many LCD panels are digital (potentially even multiplexed schemes like LVDS) this one is actually analog - more like say, VGA, and a register-programmable VGA interface might be where you could start to drive it. Or you could use a conceptually similar FPGA project or software in a very high speed MCU, or a synchronous serial engine in a medium speed one, particularly if you would settle for all-or-nothing on each color, or else a few resistive ladder bits - otherwise you need a video-speed DAC channel per color or to multiplex your colors as described in the next paragraph.

It also appears that there is a separate dot/sampling clock for each color, permitting the three colors to be driven in turn (likely if they are being decoded from a composite source, or if there is only one DAC). However, if you set the MOD input high and ground CPH2 and CPH3, it appears you can use CPH1 as a single dot clock for all of them so you could use independent color channels like in VGA. See the data sheet for the required timing between the CPH1 edge and data validity.

You will also of course need to supply some slightly obscure voltages for the operation of the LCD itself, typically provided by switching converters on whatever is doing the driving, and formally there are power sequencing requirements (perhaps you could re-use the original board for that?). And you will need to insure that all of your signal and clock (strobe) voltages match the ranges on the data sheet, which may require some simple analog networks to achieve.

There are some LCDs which will tolerate having data clocked into them at rates far, far below those specified by the data sheet. The actual rates here seem to be something you would have to deduce from the given clock pulse width and duty cycle range, but you can also try others.

This also is not a project you would likely want to attempt without access to a 20 MHz or so dual channel scope, not only to check your implementation but also potentially to examine the output signals from the original driver if there are details you have trouble deducing from the data sheet.

Keep in mind that this is not a very impressive LCD - if you do the project, do it for the adventure, not the result.

\$\endgroup\$
2
  • \$\begingroup\$ Does it use analog to control pixel positioning? If so, that's really weird. \$\endgroup\$
    – user148298
    May 23, 2016 at 0:41
  • \$\begingroup\$ No, like VGA it uses analog to communicate pixel intensity. As the data sheet shows, the timing strobes are digital, again like VGA - though the exact signals and timing differ. \$\endgroup\$ May 23, 2016 at 0:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.