Posted by Druin on 9, 2000 at 10:54 PM:
In Reply to: please help me with uing a multimeter!!!!!!! posted by charlie on 9, 2000 at 9:56 PM:
Set the meter for continuity. This setting might have a symbol on the meter like a diode schematic (straight line perpendicular to a triangle that points at this line) so when you touch the leads together, you should get a beep or something.
Assuming that's all fine, then assuming that when you press a keyboard key, you do get a direct electrical connection between its 2 pads (not sure how computer keyboards work, some have weird methods of operation) the goal is to press a keyboard key of interest and try to find the row/column wires.
Another assumption, that you know where the row/column pins are on the ICs of the keyboard, or that you don't mind probing around all day, one method to figure out the row/col with the meter is to just keep a key held somehow, and just start touching the probes to 2 possible matrix pins until you get the beep. If you do get a beep it may or may not be from that key being pressed, so to verify, release the key and see if the beep stops on the meter.
Ideally you want to know where your row/column wires are rather than just randomly touching the meter to places. Pick a keyboard key that's close to the chips and try to trace a few of the paths and make a good guess as to what pins on the chips are the matrix inputs.
So if you think you found a row/column combination for a certain key, verified by pressing and releasing the key to see that the meter detects the closing/opening, then try another key and probe around. Eventually there should be a similarity showing up where some keys have one of the same pins in common with the other one varying. You can somehow plot out a matrix from that.