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I am trying to hack a Wireless USB Keyboard (Microsoft Wireless Keyboard 2000) to create an external power button.enter image description here

The problem here is that, as you could see from the image there are four output terminals from each key centre. What two terminals should be connected to the wires so that they could be directed to an external switch?

Also is it possible to remotely access a key, for example let's take the Enter Key through USB in case of laptop?

shadesofpurplegreen
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  • It's been a while since I've opened up a keyboard. But aren't those four terminals really just two different conducting wires on different layers that are pressed together when a key smashes down on them? Used to be that way. Your picture isn't good enough for me to separate any possible layering, though. Can you see if these traces occur on two different sheets? – jonk Oct 13 '16 at 11:09
  • All 4 of the traces you're seeing are connected together already - they're all the same connection. The other half of the 'button' is on a different layer. You need one wire from one layer and another wire from the other layer. – brhans Oct 13 '16 at 11:11
  • Nope. It's actually a single layering. I just checked out now. Not on two different sheets. – shadesofpurplegreen Oct 13 '16 at 11:11
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    There is no way these are on one layer. There are to many crossing conductors not to be. This looks like it's using clear film for the substrate. The light gray circles are holes in -one- of the layers. The 2 layers are sandwiched together. If this is the case you maybe able to peel them apart and attach to the different conductors. You may be able to solder to the conductors but I bet you can't. – Spoon Oct 13 '16 at 12:13
  • Can't we control the keys in some way? – shadesofpurplegreen Oct 13 '16 at 12:15
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    I can see more than 4 traces on most of those buttons - ~4 on one layer (grey) and more on another layer (white) partially occluded by the grey traces. – Majenko Oct 13 '16 at 12:17
  • @shades: See https://electronics.stackexchange.com/questions/179275/soldering-on-keyboard-controller-circuit-board/243881#243881. – Transistor Oct 13 '16 at 16:04

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Common keyboards contain switches distributed on a 2 dimensional grid which are continuously scanned.

This is just an example. Do not assume this is the schematic of your keyboard!

(This is just an example. Do not assume this is the schematic of your keyboard!)

Therefore to remove 1 switch from the grid and re-purposes it requires adding wires across the columns and row such that the current path is not broken for the balance of the switches in the same column and / or the same row.

Almost all common (low price) keyboard are manufactured using thin plastic PCBs. Which makes this task very difficult. Take care not to effect the thin spacing maintained by the center plastic sheet.

Also is it possible to remotely access a key, for example let's take the Enter Key through USB in case of laptop?

Common keyboards generate a unique code for each key press and key release. I believe this information is passed to the USB Host (the keyboard is the USB Device) using the USB HID protocol. If so, the HID device driver on the USB Host (your computer) is where these codes are turned into codes (likely ASCII) which then get passed to the applications (like word processors and spread sheets).

If you were going to intercept a specific key and act upon it you would have to decode the USB HID protocol inside the USB connection. Not a trivial task.

Consider using a COTS USB KVM switch with LEDs to indicate which computer it is connected to. Activate your power supply when the computer 1 LED indicator is on. Now use the KVM keyboard switch sequence to control power.

st2000
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