Capacitive touch sensing

Presenting “6buttons”; a simple six button keypad based on the QProx QT160 charge transfer proximity sensor chip.

More details to come later, wanted to get some pictures and video online tonight.

simple schematic – i plan a “backpack” pcb which will provide some visual feedback, a clicking noise and translate the six outputs into an i2c bus device.

the brains of the operation, this chip does all the work. special mylar capacitors are required for it to work properly. i tried cheap-o ceramics with terrible results. the orange thing is a 10mhz resonator.

the “buttons” are printed out on plain paper, using the silkscreen layer from my pcb layout program. the capacitive dielectric is provided by the FR4 pcb material, the paper and a 1/8th inch thick layer of plexiglas; I guess you call that a multilayer capacitor!

the sensors are simple copper rings, which radiate the electrostatic field this chip uses to sense proximity. a ground plane pour around the IC helps to minimize cross-talk between sensor channels and prevent stray fields from detecting proximity around the chip itself. the capacitors near the chip also sense proximity and will need to be shielded with aluminum foil or something.

forgive the craptastic music in the video!

edit: also read Capacitive Sensing Continued

7 Replies to “Capacitive touch sensing”

  1. Thought I’d just say, good job on your keypad. I’m working on a project for the Q-Prox series touch sensor too. Planning on making a touch sensor to pop open my car doors with the sensor either behind the glass or hidden in the plastic side molding or mirror housing.

  2. Pingback: Touchsensor

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