Wednesday, 7 January 2015

Wiring little wires to stuff or “How did I get fingerprint scanner”

So I had/have a semi-old dead laptop. The motherboard is dead, everything else works. It’s a Dell XPS M1330. It has a fingerprint scanner that made my curious. How does it work? How is it connected and can I use it?

I ripped the laptop open and extracted all kinds of fun stuff including the fingerprint sensor.

It has a little chip with a writing  / / TCD42A1DN0 / /

So I started investigating.

First thing that threw me off was the 6 pin ribbon cable (USB typically uses 4).

  • Finding ground pin is the easiest – Found that.

  • Found the power pin- It was a line that had a capacitor connected with the ground. So I assumed this was the power pin.

  • Two pins are unpopulated.

  • Two pins are connected to resistors – starts to seem like USB data lines~.





Interfacing it.

Typically all internal laptop stuff uses 3.3V. So that seemed a safe way to go. I need to use a voltage converter to step down from 5V.

It has a ribbon cable, so that’s a no go. Removed that and the plug and decided to connect wires directly to it.

This needs some soldering under a microscope because this stuff is tiny.

Soldered everything up and time to test.

USB data + and –  //connected it randomly, 50/50 chance that it goes correctly the first time. (But in real life I connect it always backwards the first time.)



Connected it a perforated board and hooked up the USB cable.



Time to roll

Connected to a computer. Windows detected it (Data+ and Data- went right ways the first time). Windows installed drivers automatically and restarted the computer.


Voila, it is working!