Question Reusing Fingerprint Scanner From Laptop

[Chris127]

Hi to whoever sees this I have recently taken apart an old laptop I have lying around at home (Dell Latitude E6420) and found the fingerprint sensor component inside. I have seen a couple of YouTube videos explaining that these mostly follow USB protocol and you can wire them up to a USB cable and then use with another PC. I was very keen to do this. The issue was, all of the YouTube videos were using a different fingerprint sensor, and didn't explain at all how to find out which pin/contact to connect to which wire inside of the USB cable. I know that you can do it with a continuity tester in a multimeter, but I have no idea how. Would someone be able to explain to me how to find out which pins are 5V, D+, D- and GND? The model is PK090009D2L.
Thank you in advance.

 

[hotaru.hino]

Look at where on the circuit board the cable is connected and follow the traces from there. If they go to a chip that has leads on the sides, then it's a matter of identifying the chip and its datasheet for the pin out.

 

[Chris127]

Hi @hotaru.hino . Seems like a great idea. How do you recommend going about identifying what these chips are?
Thanks

 

[hotaru.hino]

Hi @hotaru.hino . Seems like a great idea. How do you recommend going about identifying what these chips are?
Thanks

There should be markings on the chip consisting of numbers and letters. Putting that in Google typically gets you something

 

[Grobe]

There may be used either a non-standard connector or a general connector (used to USB in this particular case) on the main board. Most probably the pinout follows usb standard, and have a look to see if there is visible pin numbers at the motherboard.

Nb: If you don't know the basic about using a multimeter, I'm not sure this is a good idea (only if only for fun by testing and damaging either computers doesn't matter for you).

 

[Chris127]

There may be used either a non-standard connector or a general connector (used to USB in this particular case) on the main board. Most probably the pinout follows usb standard, and have a look to see if there is visible pin numbers at the motherboard.

Nb: If you don't know the basic about using a multimeter, I'm not sure this is a good idea (only if only for fun by testing and damaging either computers doesn't matter for you).

Hi @Grobe . I did what you suggested and checked on the motherboard of where this fingerprint sensor used to plug in. I did manage to locate some pin numbers/letters above the connecter on the original motherboard, I just have no idea what they could mean. The six pins are labelled from left to right like this: Arrow, J, B, I, O or 0, 1. Any idea how these translate to USB format?
Thank you

 

[Grobe]

The six pins are labelled from left to right like this: Arrow, J, B, I, O or 0, 1. Any idea how these translate to USB format?

afaik. it doesn't. Regular USB devices use 4 wires, have a look at this guide:
https://www.wellpcb.com/usb-pinout.html

However - this is just my guessing (and I haven't read into the basic working of this devices): If the fingerprint scanner are used to unlock the laptop, the extra wires may exist so that they can transmit a physically signal to motherboard in order to allow system boot. If that is the case, I don't know how to tell the different between those wires and the pair of usb data transfer wires.

 

[jasonf2]

My two cents here. Even if you can identify the chips I would shy away from this if you don't have strong electronics experience or a computer you are ready to throw away. A new USB fingerprint reader is along the lines of $40. Depending on the reader in question it may be using TTL, USB or some other serial interface voltage levels. These all have different voltage levels that can potentially do damage to your computer. I have seen things as simple as USB port shorts/backfeeds that have resulted in needing new motherboards. If it is TTL (which is often done to keep things as cheap as possible) the intrinsic immunity to an "oops" is pretty low. Even if you can get it plugged in and operating drivers will potentially and probably be problematic. If you are going to go forward look up the chip and find a pinout schematic first and verify what and where the signal is and find drivers for your os. Without an oscilloscope finding signal leads and differentiating them from power source is pretty much impossible. A multimeter will tell you if voltage is present and the average amplitude of the voltage, but it really is useless for signal detection. Even if you had a scope there is a steep learning curve to setup, read and interpret what you see.