Arduino UNO capacitive sensor not working

Question

This is a visualization of my Arduino connections:

I wish to read the data using the Capacitive sensor Library. iv'e tried the following code but variables total1, total2, total3 always have the value 0 and i don't know what is wrong.

My code:

// Import the CapacitiveSensor Library.
#include <CapacitiveSensor.h>


// Name the pin as led. 
#define speaker 11


// Set the Send Pin & Receive Pin.
CapacitiveSensor   cs_2_3 = CapacitiveSensor(2,3);        // 10M resistor between pins 4 & 2, pin 2 is sensor pin, add a wire and or foil if desired
CapacitiveSensor   cs_2_4 = CapacitiveSensor(2,4);        // 10M resistor between pins 4 & 6, pin 6 is sensor pin, add a wire and or foil
CapacitiveSensor   cs_2_5 = CapacitiveSensor(2,5);        // 10M resistor between pins 4 & 8, pin 8 is sensor pin, add a wire and or foil
CapacitiveSensor   cs_2_6 = CapacitiveSensor(2,6);        // 10M resistor between pins 4 & 8, pin 8 is sensor pin, add a wire and or foil
CapacitiveSensor   cs_2_7 = CapacitiveSensor(2,7);        // 10M resistor between pins 4 & 8, pin 8 is sensor pin, add a wire and or foil
CapacitiveSensor   cs_2_8 = CapacitiveSensor(2,8);        // 10M resistor between pins 4 & 8, pin 8 is sensor pin, add a wire and or foil
CapacitiveSensor   cs_2_9 = CapacitiveSensor(2,9);        // 10M resistor between pins 4 & 8, pin 8 is sensor pin, add a wire and or foil


void setup()                    
{
  cs_2_3.set_CS_AutocaL_Millis(0xFFFFFFFF);     // turn off autocalibrate on channel 1 - just as an example

  // Arduino start communicate with computer.
  Serial.begin(9600);
}

void loop()                    
{
  // Set a timer.
  long start = millis();

  // Set the sensitivity of the sensors.
  long total1 =  cs_2_3.capacitiveSensor(60);
  long total2 =  cs_2_4.capacitiveSensor(60);
  long total3 =  cs_2_5.capacitiveSensor(60);
 /* long total4 =  cs_2_6.capacitiveSensor(60);
  long total5 =  cs_2_7.capacitiveSensor(60);
  long total6 =  cs_2_8.capacitiveSensor(60);
  long total7 =  cs_2_9.capacitiveSensor(60);*/



  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");                    // Leave some space before print the next output
  Serial.print(total2);                  // print sensor output 2
  Serial.print("\t");                    // Leave some space before print the next output
  Serial.print(total3);                  // print sensor output 3
  Serial.print("\t");                    // Leave some space before print the next output
  Serial.print("\n");
}

Answer 1

As found on the Capacitative Sensor Library page (emphasis added):

• 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. Also if the sensor is exposed metal, it is possible that the send pin will never be able to force a change in the receive (sensor) pin, and the sensor will timeout.
• Also experiment with small capacitors (100 pF - .01 uF) to ground, on the sense pin. They improve stability of the sensor.

The two emboldened points suggest that for a touch-piano, it would likely be advantageous to use a lower value resistor such as 1MΩ. Because the sensitivity increases as the resistor value increases, you want to use the lowest possible resistor value to reduce jitter & interference among your signal wires.

---

Also, later on the page:

The grounding of the Arduino board is very important in capacitive sensing. The board needs to have some connection to ground, even if this is not a low-impedance path such as a wire attached to a water pipe.

Ensure the Arduino is not run from a battery or unplugged laptop. For capacitative sensing to work, a stable ground connection is needed (via a DC plugpack or USB wall-wart is fine).

As a general note, try testing with only one capacitative connection first, then when that works, re-add the others.