#ADCTouch

ADCTouch is a library that allows users to create a capacitive sensor without ANY external hardware.

##Purpose

Most capacitive touch libraries require two pins and a large resistor to acquire precise readings. This library makes use of the AVRs internal wiring to get decent resolution with just a single pin.

##Usage

int val = ADCTouch.read(byte analogChannel, int samples = 100);

+analogChannel: the pin to use, you can just use A0 - A5

+samples: (optional) the amount of samples to take, defaults to 100

...range 1 - 65535

...(value does not change with different amounts of samples)

##How it works

To Acquire a reading, the library does the following:

+charge the test pin to 5V via pullup resistor (not directly to prevent short circuits)

+discharge the internal ~14pF capacitor

+set the pin to tristate

+connect the 14pF capacitor with the pin so that charge distributes evenly

+measure the voltage of the internal cap with analogRead()

...if the pin has a low capacitance, the stored charge will be small as will the resulting voltage, if the external capacitance is equal to 14pF, the volatage should be ~2.5V. Even higher capacitances will result in volatges > 2.5V. The chip and arduino board already have stray capacitances that will produce an output of ~390 and just a single external wire can boost that up to 500, so you really need offset compensation.

The accuracy is really good, most often even the LSB/smalles digit can still yield usable data and just vary by a single unit between readings (at only 100 samples, more will mean even less variation). The sensitivity is phenomenal, with a large enough surface, it can sense a person in more than 2 feet distance.

A more accurate explanation can be found [here](http://tuomasnylund.fi/drupal6/content/capacitive-touch-sensing-avr-and-single-adc-pin)

#include <ADCTouch.h>

int ref0, ref1; //reference values to remove offset

void setup()

{

// No pins to setup, pins can still be used regularly, although it will affect readings

Serial.begin(9600);

ref0 = ADCTouch.read(A0, 500); //create reference values to

ref1 = ADCTouch.read(A1, 500); //account for the capacitance of the pad

}

void loop()

{

int value0 = ADCTouch.read(A0); //no second parameter

int value1 = ADCTouch.read(A1); // --> 100 samples

value0 -= ref0; //remove offset

value1 -= ref1;

Serial.print(value0 > 40); //send (boolean) pressed or not pressed

Serial.print("\t"); //use if(value > threshold) to get the state of a button

Serial.print(value1 > 40);

Serial.print("\t\t");

Serial.print(value0); //send actual reading

Serial.print("\t");

Serial.println(value1);

delay(100);

}

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# Syntax Coloring Map For ADCTouch

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# Datatypes (KEYWORD1)

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ADCTouch KEYWORD1

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# Methods and Functions (KEYWORD2)

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read KEYWORD2

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# Constants (LITERAL1)

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name=ADCTouch

version=1.0.0

author=martin2250

maintainer=martin2250 <martin.225@web.de>

sentence=Create Touch Sensors with a single (Analog)Pin without external Hardware

paragraph=This library uses the internal wiring of AVR microcontrollers to measure capacitance as described here <http://tuomasnylund.fi/drupal6/content/capacitive-touch-sensing-avr-and-single-adc-pin>

category=Sensors

url=https://github.com/martin2250/ADCTouch

architectures=avr

#include "Arduino.h"

#include "ADCTouch.h"

int ADCTouchClass::read(byte ADCChannel, int samples)

{

long _value = 0;

for(int _counter = 0; _counter < samples; _counter ++)

{

pinMode(ADCChannel, INPUT_PULLUP);

ADMUX |= 0b11111;

ADCSRA |= (1<<ADSC); //start conversion

while(!(ADCSRA & (1<<ADIF))); //wait for conversion to finish

ADCSRA |= (1<<ADIF); //reset the flag

pinMode(ADCChannel, INPUT);

_value += analogRead(ADCChannel);

}

return _value / samples;

}

ADCTouchClass ADCTouch;

/* ADCTouch.h - Library for Capacittive touch sensors using only one ADC PIN Created by martin2250, April 23, 2014. Released into the public domain.*/#ifndef ADCT_h#define ADCT_h#include "Arduino.h"class ADCTouchClass{ public: int read(byte ADCChannel, int samples = 100);};extern ADCTouchClass ADCTouch;#endif