Arduino Tutorial: Capacitive Touch Sensors

For most capacitive sensing related projects, I used the CapSense library. The arduino playground has a good explanation of the Capsense library. However, if you are a novice in Arduino, I’ m pretty sure you’d understand only half of what’s written there. Therefore here I have a simplified explanation…

Capacitive Sensing:

Capacitive touch sensing is a way of human touch sensing, that requires little or no force to activate. It may be used to sense human touch through more than a quarter of an inch of plastic, wood, ceramic or other insulating material (not any kind of metal though), enabling the sensor to be completely visually concealed.

Why Capacitive touch?

• Each touch sensor requires only one wire connected to it.
• Can be concealed under any nonmetallic mmaterial.
• Can be easily used in place of a button.
• Can detect a hand from a few inches away, if required.
• Very inexpensive.

How does it work?

The sensor plate and your body forms a capacitor. We know that a capacitor stores charge. The more its capacitance, the more charge it can store.

The capacitance of this capacitive touch sensor depends on how close your hand is to the plate.

What does the Arduino do?

Basically the arduino measures how much time the capacitor (i.e the touch sensor) takes to charge, giving it an estimate of the capacitance.

The capacitance may be very small, nevertheless the Arduino measures it with accuracy.

One way of using capacitive touch in a project is to use the CapSense library. For the Capsense library, the arduino uses one send pin and any number of receive pins required. A receive pin is connected to the send pin via a medium to high value resistor.

Here are some guidelines for resistors but be sure to experiment for a desired response.

• Use a 1 megohm resistor (or less maybe) for absolute touch to activate.
• With a 10 megohm resistor the sensor will start to respond 4-6 inches away.
• With a 40 megohm resistor the sensor will start to respond 12-24 inches away (dependent on the foil size). Common resistor sizes usually end at 10 megohm so you may have to solder four 10 megohm resistors end to end.One tradeoff with larger resistors is that the sensor’s increased sensitivity means that it is slower.

*These resister value guideline is only for using the CapSense library. The last project doesn’t use this library.

Summary: Capacitive touch sensors require little or no force to activate. The CapSense library can be used to make multiple touch sensors with Arduino.

Step 2: CapSense Library Demo Code…

CapacitiveSensor   cs_4_2 = CapacitiveSensor(4,2);

 void setup() {

cs_4_2.set_CS_AutocaL_Millis(0xFFFFFFFF);    

 // turn off autocalibrate on channel 1 - just as an example

 Serial.begin(9600);}

long total1 =  cs_4_2.capacitiveSensor(30);

Serial.println(total1);

CapacitiveSensorSketch.pde1 KB

For more detail: Arduino Tutorial: Capacitive Touch Sensors