Building a portable Raspberry Pi workstation from a foldable 4.3″ screen

For ages, I’ve been meaning to take one of these 4.3 inch TFT screens and embed a Raspberry Pi inside it. I realise, of course, that the resolution of the screen isn’t anything much (certainly not “high resolution” as it states on the description!) at 480px x 272px (ish) but it’s very cute the way it just “pops up” when you press the button and there seemed to be enough space in the bottom for a Pi. So, I went ahead and bought one. It arrived the next day and I went down to The Den (my shed) to take it apart. On opening my tool draw, I found a foldable 4.3″ screen… that’s right… I’d bought something I already owned… Never mind, eh!

The base

I took the bottom off it and took a look to see what the possibilities were. To my surprise, the screen driver board was tiny (more on that later) and there was plenty of room. Not for a full Pi 3, maybe, with it’s pre-soldered 40-pin header, but a Zero W would fit in very comfortably. I took a rotary tool to some of the base plate supports (but not the screw ‘tubes’):

The driver board

The problem with these mini-screens is that they are primarily designed to be used as reversing-camera screens inside cars. That means that they are expecting a 12V power supply. They come with a cable that contains two composite inputs and a barrel jack for a 12V supply. This cable is pre-soldered onto the driver board. I knew, based on the work of other people (including SK Pang, way back when) that the screen is actually powered from 5V. So, the 12V supply must be converted into 5V by components on the controller board. Knowing that I’d need to solder onto the board, I un-stuck it from the base and inspected it.

Apart from inspecting it, I de-soldered the cable from the pads top-right and then re-soldered a ground wire and a wire to be used for composite video. I then realised that, when I’d turned the board over, I’d subconsciously noticed something. You see the solder holes bottom right? They were labelled SDA, SCL, VCC33 and GND on the underside. That means that somewhere on the board was something to do with I2C. I wondered if, perhaps, the screen was powered from 3V3, rather than 5V. I could have gone to the bother of powering it up with 12V and finding a 5V point, but I thought, what the heck, I might as well see what happened.

To start with, when powered with 3V3 at that solder point, nothing happened. In fact, nothing happened when I then powered the screen with 12V. Odd, I thought. I wondered whether it needed a composite video input signal to activate the screen. So, I needed to check how the Zero’s composite video was output. I found this guide on Adafruit which told me the answer.

Close-up of the Zero. Composite video marked. Note: the signal line is on the left, the right-hand hole is ground.

Sure enough, when I manually held the composite wire and ground to the Zero in the correct place and powered the 3V3 point, the screen flickered to life. So, now I knew what I needed to do. I needed to connect the composite and ground from the Zero to the composite and ground wire already soldered and power the screen on the 3V3 line.

Power & LED

So, I needed to power both the Pi and the screen. I took the 3V3 for the screen off the 3V3 rail of the Pi and then hacked into a USB cable I had lying around for the 5V power for the Pi which would then go to a USB battery pack.

Oh, I decided to add an LED, because blinkies! There was, bizarrely, a speaker hole in the case… but no speaker. So, I decided to drill it out and add an LED with inline resistor. I passed the wires through the hole and then soldered it to GPIO 21 and GND, conveniently located at the end of the GPIO rows.

Here’s what it looked like when I finished hot-gluing everything down and rotary-tooling some holes in the base for the two USB ports.

I grabbed a microUSB shim so that I could connect up a wireless mini keyboard to my mini workstation.

And, finally, here’s a video of the workstation in use. The keyboard is actually wireless, but I hadn’t charged it, hence the cable!

20 comments for “Building a portable Raspberry Pi workstation from a foldable 4.3″ screen

  1. Manfred
    6 April 2018 at 4:56 pm

    Nice neat job, well done.

    Did you confirm what voltage the power stage puts out (3.3 or 5)?

    If 5 then other possibilities arise:
    Powering the pi from the controller.
    Having a switchable 12 or 5 volt input.

    • Michael Horne
      7 April 2018 at 9:17 pm

      No, I didn’t. I just saw the 3v3 and thought Bingo! 🙂

  2. CJ
    8 April 2018 at 1:08 pm

    Is there any particular reason you powered the pi through the GPIO rather than USB?

    • Michael Horne
      8 April 2018 at 6:48 pm

      I thought to start with I was going to have to branch off the USB line to power the screen and Pi independently. In retrospect, it would have been better to power the thing from microUSB, yes. 🙂

  3. FunkyPiwy
    8 April 2018 at 8:38 pm

    Thank you so much Michael for this insight!
    You got me hooked and ordered the very same to try it out… Along with some other “tweaks” if there is enough space in it.
    Cheers! 🙂

    • Michael Horne
      8 April 2018 at 9:05 pm

      Let me know what you manage to do – I’ve got another one kicking around! 🙂

  4. Aquifel
    11 April 2018 at 1:26 am

    Just a heads up, I love the project, but be wary of these backup camera systems. A lot of them aren’t necessarily made to be powered on consistently, there can be major heat issues when trying to use them like a normal display. I had one that was almost identical to yours where the plastic ended up melting.

    • Michael Horne
      11 April 2018 at 5:31 pm

      Eeep! That’s a warning worth heeding. Thanks! I’m hoping by powering it from 3V3 that heat won’t be a major issue, but you just don’t know!

  5. kannan
    12 April 2018 at 10:11 am

    Any insight on the power consumed by the screen and driver? hopefully this will not strain the 3v3 reg of the Pi?

    • Michael Horne
      12 April 2018 at 11:28 am

      Not really. Only that it doesn’t seem to burn the Pi out… I understand that’s not helpful. I’ll try and find out. Just need to figure out where to stick the multimeter!

      • kannan
        13 April 2018 at 4:47 am

        simple, while in Amps mode, + of the multimeter in 3v3 source of Pi and the negative of multimeter to the display board 3v3…. do let us know how it goes…

  6. 12 April 2018 at 1:48 pm

    Excellent- thanks

  7. driss
    12 April 2018 at 10:03 pm

    hi Michael, thank you for your good article. Please I have same board and cannot find the 5v hole!

    • Michael Horne
      13 April 2018 at 4:18 am

      I didn’t bother. I just wired up to the 3v3 hole near SDA/SCL.

  8. nx43d
    3 May 2018 at 9:05 pm

    Hi there,

    your idea is great. But did you know that this LCDs have an higher resolution?
    AFAIK they have 720x480px and not only 480×272. Only the driver board seems to limit the pixels. Perhaps someone has an idea how to reprogram the driver board…

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