sábado, fevereiro 16, 2013

Project 4 - Raspberry Pi - Build a cheap laptop

One of the projects that has been on my mind lately.
Finally I've got my hands on a 7” Color TFT Car Monitor (480 x 272 pixels) and successfully got an output from the Raspberry Pi. Although the video quality definitely suffers compared to an HDMI monitor, it's still a good choice to use as a console.

I did some checking and I finally decided to buy the 7 inch TFT Color LCD Car Rear View Camera Monitor Support Rotating The Screen and 2 AV Inputs
What's In The Box:

  • 1 x 7" Car Monitor.
  • 1 x Bracket.
  • 1 x Video & Power Cable
  • 1 x Remote Controller.
  • 1 x User Manual. 


  • Display Screen:Screen Size: 7 inch, Display Component: Color TFT LCD, Resolution: 480 x 234 Pixels)
  • Contrast Ratio: 100:1.
  • Video Frequency: PAL/NTSC.
  • Video Input: Two way video input.
  • Power supply: DC 12V.

The first problem to solve was the fact that it required a 12V DC input. Unfortunately the device did not have an 12V adapter to go into the monitor – only bare wires were present. 

I found the need for 12 V to be a little non-conventional, but it's the easiest and quickest way to power on the monitor. All you need to do is supply 12V DC to the red terminal of the AV cable supplied. As I said above, the red cable is only a bare wire. So, that meant I had to find another solution to the problem. 
I had to find a composite cable that I could strip and use to connect the bare wires coming out of the TFT.

The solution: an USB cable.

Having found a cable laying around the house, I got to the task of cutting and stripping it: 


The stripped cable has 4 wires:

  • Red Wire = VCC = +5 Volts
  • Black Wire = GND = Ground
  • White Wire = D- = Negative Differential Data Signal
  • Green Wire = D+ = Positive Differential Data Signal
Basically I was interested in keeping only one end of the cable that I could plug into my PC (to get +5 Volts out) and the other end I wanted to connect to the bare wires coming out of the monitor by holding each wire between your fingers and twist the strands into one solid wire for each one of the red and black connections:

As one can see on the picture above, one end of the USB Cable connects to the laptop, and the 2 black and red wires on the other end are twisted together into one solid wire for each one of the red and black connections. The keyboard is connected to the Pi. In the end I stripped 2 USB cables (grey and blue). One is to use in the living room (the blue one), the other is to use to do some further testing (the gray one in the picture above).

The red connection is not taped up, because I run out of tape...lol. Only the black one is. Be careful not to short-circuit the monitor. I've to go out and buy some tape to make the solution permanent:  

Starting the X Windows:

And there it is! It works!!!

All I have to do now is tweak the display parameters to make it brighter. To do that is just a matter of editing the config.txt located in the boot directory and try several alternative configurations until I have what I want.

I'm going to use it chiefly as console display in the living room to control my future media centre (Synology and Pi connected together...). One other possible use is the cheap laptop. For that further research is necessary (batteries, etc).  I aim at building the ultimate cheap laptop...

Happy hacking. You don’t learn to hack – you hack to learn...


4 comentários:

Anónimo disse...

Manuel, ... SACANA!!!!!

adorei esta ideia!!!! Vou comprar!!!


Anónimo disse...

Boa tarde,
Tenho um ecrã igual ao seu.
Poderia dizer-me o que colocou no seu config.txt?

Manuel Andrade

AO disse...

Nao tinha visto aqui o teu site, que grande geek que me saiste...


Manuel Antão disse...

I geek, therefore I am ...

Este foi um dos projectos mais giros que fiz...e tem dado um jeitaço! Entretanto já fiz outros, mas ainda não fiz os respectivos posts.