Why wont my ribbon cable work?

Question

Hello, I have a raspberry pi that I have been using on my tv, but I decided to make it more portable. I took a seven inch screen from and old digital picture frame and the ribbon cable seems to fit perfectly into the pi's video port, yet when I plug in the pi and the screen the screen turns on but stays white. I know that it is reviving something because if I wiggle the ribbon cable a bit the screen changes colors but when I do the same thing with the pi off it does not change colors. Also I am fairly sure that the screen's ribbon cable has 25 pins. Ideas/help?

Here are some pictures:

Before wiggling:After wiggling:

the-dubster · Accepted Answer

Sorry techpi-e I've only just seen this.

As others have said you can't just plug any old LCD screen into the Pi and expect it to work. Generally, most LCDs use a connection protocol called Low Voltage Differential Signalling (LVDS), as rew said, Pi uses DSI, this doesn't support LVDS.

There are a few ways you can possibly get it to work, the Ben Heck Show, Episode 169 gives one option, it may be a little involved for you however. Option 2 is searching for a 'driver board' on eBay, Aliexpress or similar.

Now for the not so good news. Using the picture you provided I searched and failed to find a suitable board for you, then I noticed you were using an old photo frame LCD . . . . .

It seems that the driver boards are for laptop screens, you can try 'googling' the part number off the screen yourself - you may have more luck that me.

If all else fails you could contact one of the eBay sellers with your panel details - you may be in luck.

Good luck.

Regards

WarrenW · Answer

The chances are that just plugging it in will not work. typically these screens have a chipset on them that you will need to talk to in their native dialect. Think of it as a 'driver' or interpreter for the Raspberry Pi to send the data to the screen in a manner it will be able to interpret.

Not all screens are created with the same chipset and hence you might need to do some tweaking or coding to get it to work. I hope the connectors are pin for pin compatible or you might damage the display or the Pi or both.

Can you do a better photo of the screen details please.

Cheers

Warren.

rew · Answer

The raspberry pi chip has a "connect to mobile phone screens" option in the chip. For computers the way of connecting them to a screen are called "VGA", "DVI" and "HDMI" (you may know one or more of them!), but this one is called "DSI". it is meant to remain inside a phone-like device.

When the raspberry pi came out the raspberry pi foundation decided to put on this connector and tell everybody: "we'll make a screen soon".

This connector is quite specific for the raspberry pi. It is in no way a standard cable.

In any case... the connector is 15 pins, so if your cable is 25 pins you can be absolutely sure that it won't work.

Your screen is probably "parallel RGB", and I've seen a "howto" or "instructable" that explained how to get that working. This involved something like 25 wires on the GPIO port. The first obstacle is to connect those to your ribbon cable....