Touch Sensing Building Blocks I

The “core” building-block I mentioned in my last post is nearing completion, at least, the software.

I have my microcontroller handling “switch emulation” tasks. It can emulate either group of momentary switches or a group of toggle switches. Response time is real good in a dimly lit room, and it works decently well even with the overhead fluorescents turned on.

Right now I’m working on a basic keypad PCB I can throw together, for a ‘proof of concept’ prototype. The first keypads will likely only support 6 keys, and I’ll build from there. Six keys requires twelve LEDs, six of them need direct and discrete anode and cathode connection to the microcontroller. The other six LEDs are providing bias light for the sensors to “see”.

I should have a video up tomorrow of the breadboard in action, and hopefully some pcb’s by next weekend.

7 Replies to “Touch Sensing Building Blocks I”

  1. I’ve been loking fr a reasn to learn micrcntrllers, this might be it.

    editors note: removed external link to commerical website

  2. …. I’ve followed this LED sensing stuff for quite a while and I just wonder if it is possible to handle the sensing LEDs just as a binary switches thus avoiding the need for an ADC logic [ of course, some pre-conditioning will be needed ].

    In my line of thought, I’ll try to add this LED sensing [ on/off ] into some audio gear that I do in order to digitally select the audio source, volume [ just up/down kind of control ] with an array of 4 LEDs per indicator/switch covered by a glass… in any case WOW..!!! it is remarkable what you have done…!!!

    Greetings from Mexico….!

  3. …. by the way… in order to avoid the lighting issues… What about modulating the ‘lighting’ LEDs?, So, you can declare a valid ‘1’ or ‘0’ only when a pulse train has been detected by the ‘sensing’ leds, it will take more than 1ms to detect a valid state regardless the light conditions but it could be worthwhile the exercise….

    Just my 2cents…


  4. to use the leds as binary sensors/switches, there are two ways … the first involves still using the ADC, along with accumulators in software … the second is to use the schmitt trigger inputs on the uC … the ST inputs are sensitive enough (high enough impedance?) to register the tiny tiny current an LED produces via the photovoltaic effect … so an LED thats being lit registers as a logic high, a dark led = low.

    this makes it super easy, problem is, most pics have very few ST inputs, some models don’t have any…

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