PS2 keyboard has four wires to it: green (clock), white (data), red (positive) and black (ground). A single-throw switch is connected to the keyboard lines that give the Caps Lock signal. When connected to a computer PS2 port, the Caps Lock LED can be successfully toggled on and off.
The question: can this keyboard (particularly the Caps Lock key) be used without a computer? The Caps LED flashes when 5V is applied to the red and black wires. An attempt was made to satisfy the need for keyboard and clock inputs; after reading http://www.computer-engineering.org/ps2protocol/ , I connected 2200 ohm resistors between the clock and data lines and +5V, but to no avail. :~ Can anyone suggest a way to hack the keyboard circuitry or supply to it so that the Caps key will toggle without actual data and clock connection?
The intention is to use this toggle function to toggle another circuit. No Arduino mentioned, but I do own one Any input/tips much appreciated.
Not really. Well, yes there is, but practically no. I don't think the keyboard itself processes the caps-lock function - it actually passes the pressing of caps-lock to the computer, the OS keeps track of the current state, then passes back whether the light should be on or off. Easy way to tell for sure if a computer is completely locked up or just temporarily unresponsive is to try to toggle caps-lock or scroll-lock. If the lights don't change, something has gone seriously wrong.
The only thing you could do without interfacing the keyboard to a microcontroller is open up the keyboard, find the wires for the key and indicator light and try to solder in your own toggle circuit (caps-lock is just a momentary switch, not a latched toggle), but any keyboard that was made to the PS2 standard is probably going to be a flex circuit board with those little rubber / carbon switches and probably an epoxy blob IC, so that's going to be hard, if not impossible to modify.
With that being said, it's probably not as hard as you think to interface it to a microcontroller. I've never done it, but I know it's been done before.
any keyboard that was made to the PS2 standard is probably going to be a flex circuit board with those little rubber / carbon switches and probably an epoxy blob IC
Well, it's about that. Let me just say the experiment got me hacking my alarm clock and the failing membrane switches are now paralleled with tactile switches. Regarding the toggle, the obvious thing to do is to build it myself from basic components. While a microcontroller could communicate with a keyboard or serve as a toggle switch itself, either option is overkill. Thank you again for giving perspective to my question.
Any input/tips much appreciated.