|Cheap car back-up monitor for Raspberry Pi without the stand|
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|
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|
|Another back-light connector for the display?|
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|
|Touchscreen film over the cheap car back-up monitor|
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|
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? :)