Free Touchscreen in cheap car back-up monitor for Raspberry Pi

I have a great find to share with everyone, I found a resistive touchscreen sensor embeded in a cheap car back-up monitor that i was using for the Raspberry Pi.

Cheap car back-up monitor for Raspberry Pi without the stand

As you can see, I have removed the stand/leg thing because it was standing in my way. I bought this from BestBuy because I wanted it then and didn't want to wait for a week for one to ship from eBay (I overpaid by double I think).

The story goes like this. I received my Raspberry Pi almost a year ago and I wanted it to be stand-alone so I gathered a keyboard a mouse a power adapter and a screen for it. I wanted everything to be cheap so I went for this small screen thinking it will suffice for what I was doing.
I haven't done much with the setup but recently I came across this portable Pi and noticed the same screen as mine and all looked nice. The thing I wanted to do is to modify my screen as well to work off of 5V. I followed that guide and the hack was done.

Cheap car back-up monitor modified to work on 5V

As you can see all you need is a red wire to the small cap and a black wire (it is the one crossing over the red one) soldered to the plug's original black wire. I didn't want to cut the original power source or use the cable since I might accidentally put 12V instead of 5V.
I wanted to test it before putting it back together to make sure everything works. Results were good and was ready to put it together.

Now the interesting part
I don't know why I looked, but I unscrewed the PCB and looked at the screen and saw 2 things standing out:
1.This is pretty normal, a set of thicker wires connected to the ribbon cable to provide power to the back-lite of the screen (on the back of the ribbon cable facing the display)

The back-light connector for the display

2. Another set of thick wires that at first appear to do the same thing (I attached wires to this later one to test my hunch).

Another back-light connector for the display?

I might not seam like much, but having 2 thick connectors on a display usually says it has a touchscreen film on it. To be sure I separated the display from the cases. It is not hard but the front protective transparent plastic has glue on the black parts of it that keeps it together to the cases and the screen in place.
If you look closely in my first image you will see that I cut off the whole transparent part of the outer layer to be able to reach the touch sensor.

Touchscreen connector for the film attached to the display

As you can see, the previously mentioned connector goes on the outside of the display, now it is clear, this is a resistive touchscreen film because there is no way the back-light would be over the display, it needs to be under the polarized films and all of that.

Touchscreen film over the cheap car back-up monitor

Here you can see better that there are some patterns on the edges of the screen.
Now this makes perfect sense for anyone that has looked at this screen when turned on. The text is not quite clear and a bit hard to read, I suspect that the minuscule traces that are needed on this touchscreen film are the cause of some of the blurry details.
Anyway this is a great find and I wanted to see if it works, so I researched what I needed to do and started build it. As you can see I soldered 4 wires to the connector (removing it from the ribbon connector all together) and then found a way to close everything up beautifully. Still I had to first cut the front casing to allow me to reach the display. This is what came out:

Front casing cut off from the cheap car back-up monitor

Support leg removed from cheap car back-up monitor

Cheap car back-up monitor put back together

 Removing the stand was easy, just peel way the tape and unscrew the 2 screws and pull on the leg. After that everything was put back and that is the final result.
Now, to be able to use the touchscreen I needed a way to read the numbers. I found this great little stuff called the ExtraCore, just what I wanted small and powerful Arduino. I also needed a FTDI cable to be able to talk to it.

FTDI cable for ExtraCore side

FTDI cable for ExtraCore front

I soldered up the headers to the ExtraCore and had everything ready to go. On the left is the FTDI connector (as it is clearly marked on the minuscule board).

My ExtraCore ready for work

My ExtraCore back side

My ExtraCore profile view

 I didn't search a lot for code to make the touchscreen work but it is fairly confusing. All I can say that I used my favorite method of trying each combination until I got something that looked like it was usable. Seeing as all that the wires are connected to are just resistors, it won't hurt trying combination as there is nothing to burn or anything like that. I uploaded my code to SourceForge to use it if you find it easier. I just modified it to work with my setup. Also to mention that those added wires to not simply connect to analog pins on the ExtraCore, they are also connected by resistors to GND. Doing this will ensure that you get a 0,0 when there is nothing touching the screen and a non-zero value when you are touching it.

Connected touchscreen sensor to ExtraCore and sending data with the FTDI cable to PC

Having all this sorted out, now all that is needed is to make the RaspberryPi interpret these numbers as clicks and drags and everything else. This will be a fun thing to do, but I do hope there something out there that already does this.

I know this is not such a huge find as finding a diamond or something, the resistive film would cost somewhere about $5 or so, but the advantage I see with this is the fact that it is pretty well integrated with the display and no added fussing around with films that are larger ore not the same aspect ratio, it is just there waiting to be used.

I hope other people will find this useful and please leave a comment so I can see what this was used for and maybe someone will do the rest of the work? :)


 Enjoy!