[Viacheslav] built a keypad that uses human capacitance to detect key presses. Unlike normal keys which close a physical connection, his project detects touch through the PCB substrate. He uses the analog comparator of an AVR ATmega8 to detect the moment of zero crossing and then measures the time it takes to discharge in order to detect key presses.
I use analog comparator to detect the moment of zero crossing and the charge is evaluated by measuring time. Builtin AVR ADC probably wouldn’t be very useful here because the charge that can be built up is very small.
Update: [Viacheslav] left a comment to let us know we had it wrong. Instead of using the ADC, the analog comparitor is used. This change has been made above.
12 thoughts on “Touch Sensitive Keypad”
But I *like* my tactile feedback. :(
Neat. Would be cool for a door lock.
I’d be more interested in this for a netbook. I could shave almost a quarter inch of thickness off of mine.
yeah… I prefer to feel up my keyboard too.
This would be cool for a casemod maybe?
That would look *awesome* on some door entry keypad, which I would love to get to building some time… Hm… I have an atmega8 or two laying around, and a programmer… Just need to find me a PC with a parallel port, or a converter to parallel for programming. Harharhar!
Correction: I use analog comparator to detect the moment of zero crossing and the charge is evaluated by measuring time. Builtin AVR ADC probably wouldn’t be very useful here because the charge that can be built up is very small.
I’ll probably have to read that about 20 times before I start to understand it but it looks like it would be useful for a future project where space is a consideration.
Tactile buttons are still king though ;)
That would be very interesting as it would add a whole new layer to the process of opening the door. Someone may find the combination but they can’t open it without knowing how you press the buttons (how much pressure is applied on each one).
Of course in reality combination locks are only used in places that lots of people need to come and go from :)
make a whole keyboard like that
Very, very good. I love it!
That is very clever, I’m impressed by the low level sensing design – good job! I also love the edge-lit cover template!
I believe this is how the mouse touchpads work. I frequently use surplus touchpads for this type of application because they easily interface with controllers. My example is here:
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