# How to drive scavenged TFT screen?

How can I drive a scavenged TFT screen, from an MP4, without its datasheet?

I'm thinking about making a low cost bluetooth wrist watch to check my messages on my phone on the go. I'm going to open-source the code and the hardware if I succeed.

I have scavenged an LCD panel, but do not know how to drive it.

Here are two photos from the TFT screen on the MP4 circuitry.

I labelled my opinions on some of those pins on the LCD.

• I don't see a question here. – Olin Lathrop Jul 17 '11 at 17:26
• How to drive TFT screen of MP4 with arduino?????? the title itself is question.. in other words how to drive a tft screen without its datasheet? – Ahmet Yildirim Jul 17 '11 at 17:38

It's very possible that you'll never find a datasheet. Reverse engineering may be your best option for understanding what you have.

I recommend that, rather than dissecting a dead one - study a live one.

I would work from the bottom up. First find the LCD lines, look for meaningful signals. Use a logic analyser or oscilloscope to determine the type of bus and the shape of a transaction.

For example, for SPI you'd see a chip select, a square wave clock and two data lines. For RGB video, you might see three analogue ouputs with luma components. Or, for CVBS/Composite you might observe a colourburst.

Once you can take some action on the original device and predict the signals to the LCD, you can clone it.

Build a software implementation on your microcontroller to output the same patterns. Observe that it drives the LCD in the same way.

Alter the behaviour of your software driver repeatedly in small meaningful ways to discover how inputs relate to outputs. Try to determine the effect of flipping bits in the data and the effects they have, use this to guess at the data format.

The simple answer is - you don't.

I recently looked into the exact same thing.

Unless you have a TFT with built-in video memory and some simple low-speed interface you will need something powerful enough to generate a stream of 8 bit parallel data at typically around 27MHz (depending on the screen resolution etc).

Certainly not something an arduino can do.

And as for working out what to do without a data sheet? Well, there is absolutely zero chance of that. Even with a data sheet it's not an easy task - understanding the waveforms, the pin meanings, etc.

I was lucky and managed to find a data sheet for my scavenged LCD (it was from an HP printer), but still, I have put it away in a box and I may look at it at some time in the future when I have more powerful processors to hand.

• It is likely that the display has a controller, and if it has, you can easily drive it with with an Arduino. – morten Jul 17 '11 at 19:56
• It is not impossible to figure out. 18 of the 40 or so pins you see makes up the data bus, 5 are control signals, there is a reset pin and a few IM mode pins. The rest is power, backlight and ground. You can scope it if you are really determined. But displays like this (with docs) can found found for less that $10, so why bother? – morten Jul 17 '11 at 20:00 • no i couldnt find any display like this for like 10$.The closest one i found was 100\$. maybe im looking to wrong place :( . And i'll also need to buy a bluetooth chip so i think i could lower the cost with this screen. – Ahmet Yildirim Jul 17 '11 at 20:17
• img23.imageshack.us/img23/3354/mp4rj.jpg – Ahmet Yildirim Jul 17 '11 at 21:55
• On that reverse image you have: top left - flash chip. top right - MP3 player chip. bottom left - radio tuner. There may well be more electronics beneath the display as well. I can see nothing display related there at all - and given the number of pins on the display there should be something with a lot of pins driving it. – Majenko Jul 17 '11 at 22:10