Last chance to enter The Hackaday Prize.

Touch sensitive keypad

capacitive_keypad

[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.

Comments

  1. But I *like* my tactile feedback. :(

  2. Alex says:

    Neat. Would be cool for a door lock.

  3. Belenos says:

    I’d be more interested in this for a netbook. I could shave almost a quarter inch of thickness off of mine.

  4. sly says:

    @Insipid Melon

    yeah… I prefer to feel up my keyboard too.

  5. ank0ku says:

    This would be cool for a casemod maybe?

  6. Brandonman says:

    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!

  7. svofski says:

    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.

  8. sneakypoo says:

    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 ;)

  9. Pinochet's 21st century digital négligé says:

    @Alex

    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 :)

  10. aztraph says:

    make a whole keyboard like that

  11. trax says:

    Very, very good. I love it!

  12. Agent420 says:

    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:

    http://hackaday.com/2009/07/20/touchpad-and-vfd-hacking/

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 91,130 other followers