Bare Conductive MPR121 Arduino Library

A fairly feature complete library for the Resurgent Semiconductor MPR121QR2. This is a popular capacitive touch sense IC featuring:

• 12 electrodes/capacitance sensing inputs in which 8 are multifunctional for LED driving and GPIO
• Integrated independent autocalibration for each electrode input
• Autoconfiguration of charge current and charge time for each electrode input
• Separate touch and release trip thresholds for each electrode, providing hysteresis and electrode independence
• I2C interface, with IRQ Interrupt output to advise electrode status changes

This library was originally developed to support the Bare Conductive Touch Board. However, it should work fine (with adaptations) for any Arduino connected to an MPR121.

Library includes support for:

• capacitive touch sensing
• proximity mode for virtual 13th electrode
• readback of filtered capacitance measurements
• full GPIO including PWM write

Still to be implemented:

• callback attachment for interrupt pin

Requirements

• requires Wire.h library, which is part of the Arduino core (so you don't need to download anything) but you do need to include it in your .ino file
• it is the user's responsibility to include <wire.h> and call its begin() method
• before you use any of the MPR121 methods, you need to call its MPR121.begin() method, normally in setup()
• the default MPR121 I2C address for this library is 0x5C, which is used if you call MPR121.begin()
• if you want to specify a different address you can, with MPR121.begin(yourAddress)

Typical use example:

// 0x5A for a lot of boards out there
// 0x5C for the Touch Board

#define MPR121addr 0x5A

#include <Wire.h>
#include <MPR121.h>

void setup(){
	MPR121.begin(MPR121addr);
}

void loop(){
	// your code goes here
}

Install

• Arduino's instructions for installing libraries are available here

Examples

• SimpleTouch - simple capacitive touch sense sketch with output via serial
• DataStream - serial data stream of capacitance data from MPR121
• GPIOinverter - MPR121 GPIO inverter - reads one pin and outputs the inverse on another
• LEDfade - simple MPR121 LED fader

Note

The new clearSavedThresholds(), restoreSavedThresholds() and saveTouchThreshold() methods for the MPR121 object use EEPROM to save and restore thresholds automatically when setting them with the updated Grapher Processing sketch. However, if you're using a board that doesn't have the AVR architecture, your code will compile and run normally in every other way, but these functions will not work. Also, the new Datastream object's reset() method will do nothing due to the different way that watchdog timers are handled on AVR boards vs. other boards.