CapSense (QTouchADC)
Information
This is another CapSense implementation that tries to follow the specifications of Atmels QTouchADC, a version of QTouch that uses the internal Sample & Hold capacitor of the ADC. No external capacitor is needed anymore! Just make some small sensor pads, or even sliders and wheels (see Atmel Design referece).
To make the measurement more stable I used transistors to drive the LEDs (somehow it works much better when there is less current through the chip), and it is recommended to use a stable power source (batteries or add an additional capacitor between 5V and GND).
Not like in the pseudo schematic, there should be a 1k Ohm resistor between the microcontroller an the sensor pad!
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Links
forked on Github
https://github.com/dusjagr/QTouchADCArduino
More on QTouchADC
discussion on mikrocontroller.net
How to make Buttons, Sliders and Wheels
Nice description and implementation on ATMega32u4
https://www.youtube.com/watch?v=Ncu2GZJbluI
QTouch on Attiny and Arduino
Very smoothly working implementation for Arduino ->> can someone translate it to the attiny register-ports? (dusjagr tried and failed...) or even make it into a library?
Library for Arduino for ADC Touch, noisy...
TinyTouch library for attiny (I can't get this to run from the arduino IDE), looks very nice!!!
Programming the attiny85 with arduino IDE
Code
/*
NC 1 8 +5V
KEY0 2 7 NC
KEY1 3 6 LAMP PWM2
GND 4 5 LAMP PWM1
*/
#include <avr/io.h>
#include <avr/delay.h>
//------------------------------------------------------------------------------------------------------------
void init(){
// ADC
ADMUX = (0<<REFS0); //VCC reference
ADCSRA = (1<<ADEN)| (1<<ADPS2)|(1<<ADPS1)|(1<<ADPS0); //ADC enable, prescaler 128
// PWM
DDRB |= (1<<PB0)|(1<<PB1); // PWM-outputs
TCCR0A = (1<<COM0A1)|(1<<COM0B1)|(1<<WGM01)|(1<<WGM00); // fast PWM
TCCR0B = (1<<CS02); // counter clock divider 256
OCR0A = 255;
OCR0B = 255;
}
// pre: input PB3 (ADC3) and PB4 (ADC2). PB2 (ADC1) is used as reference, PB0 and PB1 for PWM
uint16_t sensePad(uint8_t adcPin){
int16_t measurement1, measurement2;
uint8_t portPin;
if (adcPin == 3) {
portPin = PB3;
} else {
portPin = PB4;
}
// first measurement: adcPin low, S/H high
ADMUX = (0<<REFS0) | 0x01; // set ADC sample+hold condensator to the free PB2 (ADC1)
PORTB |= (1<<PB2); //PB2/ADC1 ref/ S/H higt
DDRB |= (1<<portPin) | (1<<PB2); // both output: adcPin low, S/H (ADC1) high
_delay_us(32);
DDRB &= ~((1<<portPin) | (1<<PB2));
PORTB &= ~((1<<portPin) | (1<<PB2));
ADMUX = (0<<REFS0) | (adcPin & 0x03); // read extern condensator from adcPin
ADCSRA |= (1<<ADSC); // start conversion
while (!(ADCSRA & (1 << ADIF))); // wait for conversion complete
ADCSRA |= (1 << ADIF); // clear ADIF
measurement1=ADC;
// second measurement: adcPin high, S/H low
ADMUX = (0<<REFS0) | 0x01; // set ADC sample+hold condensator to the free PB2 (ADC1)
PORTB |= (1<<portPin); // sensePad/adcPin high
DDRB |= (1<<portPin) | (1<<PB2); // both output: adcPin high, S/H (ADC1) low
_delay_us(32);
DDRB &= ~((1<<portPin) | (1<<PB2));
PORTB &= ~((1<<portPin) | (1<<PB2));
ADMUX = (0<<REFS0) | (adcPin & 0x03); // read extern condensator from adcPin
ADCSRA |= (1<<ADSC); // start conversion
while (!(ADCSRA & (1 << ADIF))); // wait for conversion complete
ADCSRA |= (1 << ADIF); // clear ADCIF
measurement2=ADC;
return (measurement2 - measurement1)+1023;
}
uint8_t getMultiplicator(int16_t value, uint16_t maxValue){
if (maxValue<64){
value=value*4;
} else if (maxValue < 86){
value= value*3;
} else if (maxValue < 103) {
value = (value/2)*5;
} else if (maxValue<128){
value=value*2;
} else if (maxValue < 154){
value = (value/3)*5;
} else if (maxValue<171){
value = (value/2)*3;
} else if (maxValue<205){
value = (value/4)*5;
} else {
value=(value/5)*4;
}
return value;
}
//------------------------------------------------------------------------------------------------------------
int main(void) {
init();
int16_t senseValue1, senseValue2;
int16_t refMin1, refMin2;
uint16_t refMax1, refMax2;
refMin1 = sensePad(2);
refMin1 = sensePad(2);
refMin2 = sensePad(3);
refMin2 = sensePad(3);
for(;;){
PORTB &= ~(1<<PB3);
senseValue1 = sensePad(2);
senseValue1 = senseValue1 - refMin1;
if (senseValue1<0){
senseValue1=0;
}
if (senseValue1>refMax1) {
refMax1=senseValue1;
}
senseValue1 = getMultiplicator((uint8_t) senseValue1, refMax1);
senseValue2 = sensePad(3);
senseValue2 = senseValue2 - refMin2;
if (senseValue2<0){
senseValue2=0;
}
if (senseValue2>refMax2) {
refMax2=senseValue2;
}
senseValue2 = getMultiplicator((uint8_t) senseValue2, refMax2);
OCR0B = senseValue1;
OCR0A = senseValue2;
}
return 0; /* never reached */
}