Circuit Playground Fruit Drums

published November 15, 2016, last updated September 14, 2024

Beginner

Project guide

Hello Capacitive Touch

Since this project uses the capacitive touch capabilities of the Circuit Playground, let's start by exploring how they work. You can read some technical details in the Lesson #0 Guide. There are 8 pads total located on the edge of the Circuit Playground as shown below. Note the numbering scheme used to identify each pad: #3, #2, #0, #1, #12, #6, #9, and #10.

The library function readCap() is all that is needed to use capacitive touch. It is used the same for all 8 pads. Simply call it with the pad number of interest and it returns a value. This value will be near zero when not touched and have some higher value when touched. We can use the simple sketch below to examine how this value behaves, focusing on just one pad, #1 in this case.

Download File

Copy Code

// SPDX-FileCopyrightText: 2020 Carter Nelson for Adafruit Industries
//
// SPDX-License-Identifier: MIT

#include <Adafruit_CircuitPlayground.h>

////////////////////////////////////////////////////////////////////////////
void setup() {
  // Initialize serial.
  Serial.begin(9600); 
  
  // Initialize Circuit Playground library.
  CircuitPlayground.begin();
}

////////////////////////////////////////////////////////////////////////////
void loop() {
  // Print cap touch reading on serial port.
  Serial.println(CircuitPlayground.readCap(1));

  // Update rate.
  delay(100);
}

// SPDX-FileCopyrightText: 2020 Carter Nelson for Adafruit Industries
//
// SPDX-License-Identifier: MIT

#include <Adafruit_CircuitPlayground.h>

////////////////////////////////////////////////////////////////////////////
void setup() {
  // Initialize serial.
  Serial.begin(9600); 
  
  // Initialize Circuit Playground library.
  CircuitPlayground.begin();
}

////////////////////////////////////////////////////////////////////////////
void loop() {
  // Print cap touch reading on serial port.
  Serial.println(CircuitPlayground.readCap(1));

  // Update rate.
  delay(100);
}

This sketch only uses the #1 touch pad.

With this sketch loaded and running on the Circuit Playground, open the Serial Plotter.

Tools -> Serial Plotter

The capacitive touch value from the #1 pad will be plotted like a strip chart as shown below. Try touching the pad quickly several times and also holding your finger on it.

The readCap() function is different from the push button functions leftButton() and rightButton() which return true when the button is pressed and false otherwise. However, we can take a very simple approach to create a similar behavior for the capacitive touch pads. We compare the value returned by readCap() to a preset threshold value which we'll call CAP_THRESHOLD. If it exceeds this value, it is touched (pressed), otherwise, it is not. Here's a simple function to do just that.

Download File

Copy Code

boolean capButton(uint8_t pad) {
  if (CircuitPlayground.readCap(pad) > CAP_THRESHOLD) {
    return true;  
  } else {
    return false;
  }
}

boolean capButton(uint8_t pad) {
  if (CircuitPlayground.readCap(pad) > CAP_THRESHOLD) {
    return true;  
  } else {
    return false;
  }
}

The actual value for CAP_THRESHOLD will be defined globally. But what is a good value? Well, that will depend on your setup. If the value is set too low, you may get incorrect detections due to noise. But if you set it too high, you may never detect any touches. You could use the Serial Monitor or Plotter with the above sketch to see what values your setup returns, and then choose a value based on that. For the examples here, we will use a value of 50.

Here is another simple sketch that uses the capButton() function along with a CAP_THRESHOLD of 50 to detect when the #1 pad is touched.

Download File

Copy Code

// SPDX-FileCopyrightText: 2020 Carter Nelson for Adafruit Industries
//
// SPDX-License-Identifier: MIT

#include <Adafruit_CircuitPlayground.h>

#define CAP_THRESHOLD   50
#define DEBOUNCE        250

////////////////////////////////////////////////////////////////////////////
boolean capButton(uint8_t pad) {
  if (CircuitPlayground.readCap(pad) > CAP_THRESHOLD) {
    return true;  
  } else {
    return false;
  }
}

////////////////////////////////////////////////////////////////////////////
void setup() {
  // Initialize serial.
  Serial.begin(9600); 
  
  // Initialize Circuit Playground library.
  CircuitPlayground.begin();
}

////////////////////////////////////////////////////////////////////////////
void loop() {
  // Check if capacitive touch exceeds threshold.
  if (capButton(1)) {

      // Print message.
      Serial.println("Touched!");
      
      // But not too often.
      delay(DEBOUNCE); 
  }
}

// SPDX-FileCopyrightText: 2020 Carter Nelson for Adafruit Industries
//
// SPDX-License-Identifier: MIT

#include <Adafruit_CircuitPlayground.h>

#define CAP_THRESHOLD   50
#define DEBOUNCE        250

////////////////////////////////////////////////////////////////////////////
boolean capButton(uint8_t pad) {
  if (CircuitPlayground.readCap(pad) > CAP_THRESHOLD) {
    return true;  
  } else {
    return false;
  }
}

////////////////////////////////////////////////////////////////////////////
void setup() {
  // Initialize serial.
  Serial.begin(9600); 
  
  // Initialize Circuit Playground library.
  CircuitPlayground.begin();
}

////////////////////////////////////////////////////////////////////////////
void loop() {
  // Check if capacitive touch exceeds threshold.
  if (capButton(1)) {

      // Print message.
      Serial.println("Touched!");
      
      // But not too often.
      delay(DEBOUNCE); 
  }
}

The additional value DEBOUNCE is used to prevent the output from happening too fast. With the above sketch loaded and running, open the Serial Monitor.

Tools -> Serial Monitor

Whenever the #1 pad is touched, you should see a message printed out.