CapSense Library

Download: CapSense.zip (Version 04)

Hardware Requirements

Each sensor connects to 2 pins, send and receive. The send pin must connect with a large-value resistor, between 100K to 50M. Larger values allow more sensitivity, but with slower response. The example above uses 4.7M resistors.

The receive pin may be connected with a wire, but a 1K or higher resistor will help protect the Teensy's pin if a user directly touches the object and delivers an electro-static shock. The safest construction uses an insulating layer, such as the clear tape in the example above.

Multiple sensors can share a single send pin, but each must have its own receive pin.

Teensy's ground pin should be connected to earth ground for best results. Normally the USB cable connects to a PC, which connects to earth ground by its power code. But when using a laptop on battery power or running without a computer, you may need to make a dedicated connection to earth ground.

Basic Usage

Create the CapSense object, using a specific pair of pin. You should create a separate CapSense object for each sensor. Sensors can share the same sendPin, but each needs its own reveicePin.

Measure the sensor. The measurement is repeated numSamples times. More measurements increases sensitivity, but takes longer. The elapsed time, in arbitrary units, is returned. A negative number is returned if any error occurs.

Example Program

You can open this example from the File > Examples > CapSense > CapSenseSketch menu.

#include <CapSense.h>

/*
 * CapitiveSense Library Demo Sketch
 * Paul Badger 2008
 * Uses a high value resistor e.g. 10M between send pin and receive pin
 * Resistor effects sensitivity, experiment with values, 50K - 50M. Larger resistor values yield larger sensor values.
 * Receive pin is the sensor pin - try different amounts of foil/metal on this pin
 */


CapSense   cs_4_2 = CapSense(4,2);        // 10M resistor between pins 4 & 2, pin 2 is sensor pin, add a wire and or foil if desired
CapSense   cs_4_6 = CapSense(4,6);        // 10M resistor between pins 4 & 6, pin 6 is sensor pin, add a wire and or foil
CapSense   cs_4_8 = CapSense(4,8);        // 10M resistor between pins 4 & 8, pin 8 is sensor pin, add a wire and or foil

void setup()                    
{
   cs_4_2.set_CS_AutocaL_Millis(0xFFFFFFFF);     // turn off autocalibrate on channel 1 - just as an example
   Serial.begin(9600);
}

void loop()                    
{
    long start = millis();
    long total1 =  cs_4_2.capSense(30);
    long total2 =  cs_4_6.capSense(30);
    long total3 =  cs_4_8.capSense(30);

    Serial.print(millis() - start);        // check on performance in milliseconds
    Serial.print("\t");                    // tab character for debug windown spacing

    Serial.print(total1);                  // print sensor output 1
    Serial.print("\t");
    Serial.print(total2);                  // print sensor output 2
    Serial.print("\t");
    Serial.println(total3);                // print sensor output 3

    delay(10);                             // arbitrary delay to limit data to serial port 
}