CapTouch.cpp

/* CapTouch.cpp part of v.04 - Capacitive Sensing Library for 'duino / Wiring
* by Paul Badger 2-3-2012
* <paul@moderndevice.com> http://opensource.org/licenses/mit-license.php
*
* This capacitive sensing method requires two microcontroller pins (send pin, receive pin)
* with a high value resistor between them (1M is a starting point)
* a small capacitor (20-40 pf) from the receive pin (the sensor is connected to this pin)
* to ground will result in more stable readings. Sensor is any wire or conductive foil 
* on the receive pin.
*/

// include this library's description file
#include "CapTouch.h"

#if defined(ARDUINO) && ARDUINO >= 100
#include "Arduino.h"
#else
#include "WProgram.h"
#include "pins_arduino.h"
#include "WConstants.h"
#endif


// Constructor /////////////////////////////////////////////////////////////////
// Function that handles the creation and setup of instances

CapTouch::CapTouch(uint8_t sendPin, uint8_t receivePin){
	
	// get pin mapping and port for send Pin - from PinMode function in core
	sBit =  digitalPinToBitMask(sendPin);            // get send pin's ports and bitmask
	sPort = digitalPinToPort(sendPin);
	sOut = portOutputRegister(sPort);                // get pointer to output register   
	
	 rBit = digitalPinToBitMask(receivePin);         // get receive pin's ports and bitmask 
	 rPort = digitalPinToPort(receivePin);
	
   	rOut = portOutputRegister(rPort);
	
	if (sPort == NOT_A_PORT) {error = -1;           // this does not appear to work
	// Serial.println("bad pin");
	}
	sReg = portModeRegister(sPort);
	
	// get pin mapping and port for receive Pin - from digital pin functions in Wiring.c
	if (rPort == NOT_A_PORT){ error = -1;          // this does not appear to work
	// Serial.println("bad pin");
	}
	rReg = portModeRegister(rPort);
	rOut = portOutputRegister(rPort);
	rIn  = portInputRegister(rPort);
	
    *sReg |= sBit;              // set sendpin to OUTPUT 
	calibrateFlag = 0;          // uncalibrated on startup
	
}

// Public Methods //////////////////////////////////////////////////////////////
// Functions available in Wiring sketches, this library, and other libraries

long CapTouch::readTouch(uint8_t samples)
{
	int i;
	total = 0;
	
	// calibratess the baseline value
	// first time after powerup or reset calibrates the sensor with baseline
	// so sensor should be in "untouched" state at powerup
	
	if (calibrateFlag == 0 || samples != lastSamples){
		calibrateTouch(samples);
		lastSamples = samples;
		calibrateFlag = 1;
	
	}
		
//	*sReg |= sBit;             // set Send pin Output
	
	for (i = 0; i < samples; i++) {
		noInterrupts();        // turn off interrupts to prevent collisions with other software
		*rReg &= ~rBit;        // set receive pin to input
		*rOut &= ~rBit;        // set receive pin low to make sure pullups are off
		
		*rReg |= rBit;         // receive pin is now LOW AND OUTPUT to discharge circuit
		*rReg &= ~rBit;        // set pin to INPUT 
		
		*sOut |= sBit;         // set send pin High
		interrupts();
		
		while( !(*rIn & rBit)  && (total < timeoutCount )){  // while receive pin is LOW AND total is positive value
			total++;
		}
		
		if (total >= timeoutCount){
			return -2;             //  total variable over timeout
		}
		
		// set receive pin HIGH briefly to charge up fully - because the while loop above will exit when pin is ~ 2.5V 
		noInterrupts();
		*rOut  |= rBit;        // set receive pin HIGH - turns on pullup 
		*rReg |= rBit;         // set pin to OUTPUT - pin is now HIGH AND OUTPUT
		*rReg &= ~rBit;        // set pin to INPUT 
		*rOut  &= ~rBit;       // turn off pullup
		
		*sOut &= ~sBit;        // set send Pin LOW
		interrupts();
		while( (*rIn & rBit) && (total < timeoutCount)){        // while receive pin is HIGH  AND total is less than timeout
			total++;
		}
		
	}
	

	
	
	if (total >= timeoutCount){
		return -2;     // total variable over timeout
    }
    else
    {
		total = total - baselineR;
		
#ifdef NO_NEGATIVES
		if (total < 0)   return 0;
#endif
		
				return total;
    }
}


long CapTouch::calibrateTouch(uint8_t samples){
	
	int i = 0, j = 0;
	
	*sReg |= sBit;             // set Send pin Output
	
	// the idea here is to calibrate for the same number of samples that are specified
	// but to make sure that the value is over a certain number of powerline cycles to 
	// average out powerline errors
	
	unsigned long start = millis();
	while (millis() - start < calibrateTime){
		
		for (i = 0; i < samples; i++) {			
			noInterrupts();
			*rReg &= ~rBit;        // set receive pin to input
			*rOut &= ~rBit;        // set receive pin low to make sure pullups are off
			
			*rReg |= rBit;         // receive pin is now LOW AND OUTPUT to discharge circuit
			*rReg &= ~rBit;        // set pin to INPUT 
			
			*sOut |= sBit;         // set send pin High
			interrupts();
			while( !(*rIn & rBit)  && (total < timeoutCount )){  // while receive pin is LOW AND total is positive value
				total++;
			}
			
			if (total >= timeoutCount){
				return -2;             //  total variable over timeout
			}
			
			// set receive pin HIGH briefly to charge up fully - because the while loop above will exit when pin is ~ 2.5V
			noInterrupts();
			*rOut  |= rBit;        // set receive pin HIGH - turns on pullup 
			*rReg |= rBit;         // set pin to OUTPUT - pin is now HIGH AND OUTPUT
			*rReg &= ~rBit;        // set pin to INPUT 
			*rOut  &= ~rBit;       // turn off pullup
			
			*sOut &= ~sBit;        // set send Pin LOW
			interrupts();
			while( (*rIn & rBit) && (total < timeoutCount)){        // while receive pin is HIGH  AND total is less than timeout
				total++;
			}
			
		}
		j++;
		
	}
	
	
	 
	
	if (total >= timeoutCount){
		return -2;     // total variable over timeout
		Serial.println("calibrate routine over timeout, check wiring or raise  'timeoutCount' in CapTouch.h");
    }
    else
    {   Serial.print("total = ");
		Serial.print(total);
		baselineR = total / j;
		Serial.print(" baselineR = ");
		Serial.print(baselineR);
    }
	
	
}