Matt Nupen

Arduino capacative tin foil capacative sensor from Matt Nupen on Vimeo.

In preparation to knock the socks of my students with the arduino’s potentional I made a capactive touch sensor with some tin foil. It also acts as a proximity sensor by sensing when someone or something alters the magnetic field around the capacitor (tinfoil in this case) .

For the capacitive sensor I followed in the instructions in this forum post: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1171076259

I modified to code to light up 4 LEDs depending on how much you are interfering with the sensor. The first two light up if you move your hand closer while the last 2 light up when you touch it. Lots of fiddling with the sensitivity range, but worth it.

I also added in a piezo buzzer that changes frequency based on how close you get to it.

Code for the 4 LEDs borrowed from http://arduino.cc/en/Tutorial/BarGraph
Code for the buzzer borrowed from http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1256389806

//## SENSOR
int  i;
unsigned int x, y;
float accum, fout, fval = .2;    // these are variables for a simple low-pass (smoothing) filter - fval of 1 = no filter - .001 = max filter

//## Buzzer
int piezoPin = 3;

//## LED
int ledCount = 4;
int ledPins[] = {
 4, 5, 6, 7 };   // an array of pin numbers to which LEDs are attached

void setup() {
 Serial.begin(9600);

 DDRB=B101;     // DDR is the pin direction register - governs inputs and outputs- 1's are outputs
 // Arduino pin 8 output, pin 9 input, pin 10 output for "guard pin"
 //  preceding line is equivalent to three lines below
 //  pinMode(8, OUTPUT);     // output pin
 //  pinMode(9, INPUT);      // input pin
 //  pinMode(10, OUTPUT);    // guard pin
 digitalWrite(10, LOW);  //could also be HIGH - don't use this pin for changing output though

 // loop over the pin array and set them all to output:
 for (int thisLed = 0; thisLed < ledCount; thisLed++) {
 pinMode(ledPins[thisLed], OUTPUT);
 }

 pinMode(3, OUTPUT); // set a pin for buzzer output

}

void loop() {
 y = 0;        // clear out variables
 x = 0;

 for (i=0; i < 4 ; i++ ){       // do it four times to build up an average - not really neccessary but takes out some jitter

 // LOW-to-HIGH transition
 PORTB = PORTB | 1;                    // Same as line below -  shows programmer chops but doesn't really buy any more speed
 // digitalWrite(8, HIGH);
 // output pin is PortB0 (Arduino 8), sensor pin is PortB1 (Arduinio 9)

 while ((PINB & B10) != B10 ) {        // while the sense pin is not high
 //  while (digitalRead(9) != 1)     // same as above port manipulation above - only 20 times slower!
 x++;
 }
 delay(1);

 //  HIGH-to-LOW transition
 PORTB = PORTB & 0xFE;                // Same as line below - these shows programmer chops but doesn't really buy any more speed
 //digitalWrite(8, LOW);
 while((PINB & B10) != 0 ){            // while pin is not low  -- same as below only 20 times faster
 // while(digitalRead(9) != 0 )      // same as above port manipulation - only 20 times slower!
 y++;
 }

 delay(1);
 }

 fout =  (fval * (float)x) + ((1-fval) * accum);  // Easy smoothing filter "fval" determines amount of new data in fout
 accum = fout;

 int mappedFout;
 mappedFout = map(fout, 1100, 1400, 0, ledCount);

 //Serial.print((long)x, DEC);    // raw data - Low to High
 // Serial.print( "   ");
 // Serial.print((long)y, DEC);    // raw data - High to Low
 Serial.print(mappedFout);
 Serial.print( "   ");
 Serial.println( (long)fout, DEC); // Smoothed Low to High

 // map the result to a range from 0 to the number of LEDs:
 int ledLevel = mappedFout;

 // loop over the LED array:
 for (int thisLed = 0; thisLed < ledCount; thisLed++) {
 // if the array element's index is less than ledLevel,
 // turn the pin for this element on:
 if (thisLed < ledLevel) {
 digitalWrite(ledPins[thisLed], HIGH);
 }
 // turn off all pins higher than the ledLevel:
 else {
 digitalWrite(ledPins[thisLed], LOW);
 }
 }

 int piezoFreq = map(fout, 1100, 1400, 0, 2500);
 buzz(piezoPin, piezoFreq, 60);

}

void buzz(int targetPin, long frequency, long length) {
 long delayValue = 1000000/frequency/2; // calculate the delay value between transitions
 //// 1 second's worth of microseconds, divided by the frequency, then split in half since
 //// there are two phases to each cycle
 long numCycles = frequency * length/ 1000; // calculate the number of cycles for proper timing
 //// multiply frequency, which is really cycles per second, by the number of seconds to
 //// get the total number of cycles to produce
 for (long i=0; i < numCycles; i++){ // for the calculated length of time...
 digitalWrite(targetPin,HIGH); // write the buzzer pin high to push out the diaphram
 delayMicroseconds(delayValue); // wait for the calculated delay value
 digitalWrite(targetPin,LOW); // write the buzzer pin low to pull back the diaphram
 delayMicroseconds(delayValue); // wait againf or the calculated delay value
 }
}