Finally I have done force AVR’s to read touch buttons. Atmel QTouch library was interesting, but it was too hard form me, and it’s so big. I have rode piece of teory, have found a few examples and done. First effect is this module. How does it work in practice:
How does it workin theory: The platestouch sensorsact ascapacitors, loadedby a resistor. The microprocessorloads theRC circuit, measuring the time. SinceRis a constant, the charging time is dependent on thecapacity.Capacitance changeswhenattacha finger–he becomesthe dielectric. For the system towork, you must take care ofseveral elements: –Capacity of such a “capacitor” is very small.To extend thecharging time, usedhigh-valueresistors(I usedtheabsence of other10M, betterwould beabout 2-5M ohms). –One needs onepinsensorfor reading, andonefor loading, except that the latter maysimultaneously support multiplesensors. –Times are verysmall; Whydoes notuse thedelay; samerotationmeasurement loopis long enough. Changescapacityare alsosmall,so it is importantto make thischangeafter applyingfingerwasas large as possible. Therefore,the plateshave a surfaceina grid, to reducetheir owncapacity. Contrary tointuition, the larger thefieldof sensors, thisis not necessarilybetter. –In such systems, it is important touse asthe shortestpathto reduceharmfulcapacity. –It is also around thepouringweight, which willshield theinterferenceand provide asecond electrodeof the capacitor. –As is apparent from the above description, the measurement does not rely onthe detectioncapacity ofthe human bodyrelative to the ground, or anythinglike that.Humanfingerisdielectricof the capacitorin the electric fieldformed by thefieldof the sensorfieldand the nearbyground.
Tiny, powered from one CR1220 lithium battery RC5 code reciver, decodes on AVR ATTiny110. IC controls two LED’s in ON/OFF mode. To avoid unexpectables changes states on outputs, the Toogle bit is reading from RC5 frame.