Bare Conductive › Starter › Article 6

Loading Example Sketches

Explore the Touch Board library's built-in examples, understand what each does, and make your first code modification.

⏱ 18 min read examples Arduino sketch modify code

Finding the examples

Once you’ve installed the Touch Board library (article 5), the examples appear in:

File → Examples → (scroll down to) Bare Conductive Touch Board

The exact names depend on the library version, but you’ll typically find:

Sketch name What it does
Touch_MP3 Default firmware — touch to play MP3
Touch_MP3_Toggle Touch to toggle play/stop instead of retrigger
Touch_MP3_Proximity Uses proximity detection to fade volume
Serial_Comms Sends touch events over USB serial
MIDI_Piano Sends MIDI note messages
LED_Fade Fades an LED based on touch

Anatomy of a Touch Board sketch

Open Touch_MP3 and look at the structure:

// Include the libraries we need
#include <MPR121.h>
#include <Wire.h>
#include <SPI.h>
#include <SdFat.h>
#include <FreeStack.h>
#include <SFEMP3Shield.h>

// Define the number of electrodes
#define numElectrodes 12

// These variables track touch state
boolean touchStates[numElectrodes];

SFEMP3Shield MP3player;

void setup() {
  // Initialise serial communication
  Serial.begin(57600);

  // Initialise the MPR121 touch sensor
  if (!MPR121.begin(0x5C)) {
    Serial.println("error setting up MPR121");
    // handle error...
  }
  MPR121.setInterruptPin(4);
  MPR121.setTouchThreshold(40);
  MPR121.setReleaseThreshold(20);

  // Initialise the MP3 player
  // ... MP3player.begin() etc.

  // Reset touch states
  for (int i = 0; i < numElectrodes; i++) {
    touchStates[i] = false;
  }
}

void loop() {
  // Read touch sensor
  if (MPR121.touchStatusChanged()) {
    MPR121.updateTouchData();

    for (int i = 0; i < numElectrodes; i++) {
      if (MPR121.isNewTouch(i)) {
        // Electrode i was just touched
        playTrack(i);
      }
      if (MPR121.isNewRelease(i)) {
        // Electrode i was just released
      }
    }
  }
}

The key pattern is:

  1. Check if anything changed (touchStatusChanged())
  2. Update the data (updateTouchData())
  3. Loop through electrodes and check for new touches (isNewTouch(i)) and releases (isNewRelease(i))

Your first modification — adding LED feedback

A small change: flash the onboard LED (D13) when any electrode is touched:

// At the top of your sketch, after the includes:
const int LED_PIN = 13;

// In setup():
pinMode(LED_PIN, OUTPUT);

// In the loop, inside the isNewTouch block:
if (MPR121.isNewTouch(i)) {
  digitalWrite(LED_PIN, HIGH);
  playTrack(i);
}

// Inside the isNewRelease block:
if (MPR121.isNewRelease(i)) {
  digitalWrite(LED_PIN, LOW);
}

Upload this. Now the LED lights up while any electrode is being touched.

Modifying which sounds play

The playTrack(i) function maps electrode number to a filename. To change the mapping, modify the function:

void playTrack(int trackNum) {
  char filename[12];

  // Default: TRACK000.mp3 for electrode 0, TRACK001.mp3 for electrode 1, etc.
  sprintf(filename, "TRACK%03d.mp3", trackNum);

  // Custom mapping example: electrodes 0-5 play a major scale (different track range)
  int customMap[] = {0, 2, 4, 5, 7, 9, 11, 12, 14, 16, 17, 19};
  sprintf(filename, "TRACK%03d.mp3", customMap[trackNum]);

  if (MP3player.isPlaying()) MP3player.stopTrack();
  MP3player.playMP3(filename);
}

Touch threshold adjustment

The touch and release thresholds control how sensitive the detection is. Lower values = more sensitive:

MPR121.setTouchThreshold(40);    // default
MPR121.setReleaseThreshold(20);  // default

// More sensitive:
MPR121.setTouchThreshold(20);
MPR121.setReleaseThreshold(10);

// Less sensitive (reduces false triggers):
MPR121.setTouchThreshold(60);
MPR121.setReleaseThreshold(40);

You can also set per-electrode thresholds:

MPR121.setTouchThreshold(40, 0);   // electrode 0 only
MPR121.setTouchThreshold(20, 3);   // electrode 3 more sensitive

Serial Monitor — seeing what the Touch Board is doing

The Serial Monitor lets you print debug information from the Touch Board to your computer screen:

// In setup():
Serial.begin(57600);

// In the touch handler:
if (MPR121.isNewTouch(i)) {
  Serial.print("Touched electrode: ");
  Serial.println(i);
}

Open the Serial Monitor: Tools → Serial Monitor (or Ctrl+Shift+M). Set the baud rate to 57600.

You’ll see messages printed every time an electrode is touched. This is invaluable for debugging.

Key takeaways

  • Examples are in File → Examples → Bare Conductive Touch Board
  • The main loop pattern: touchStatusChanged() → updateTouchData() → check isNewTouch(i) and isNewRelease(i)
  • Modify playTrack() to remap sounds to electrodes
  • setTouchThreshold() and setReleaseThreshold() control sensitivity — lower = more sensitive
  • Serial.println() + Serial Monitor is your best debugging tool