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MPR121 Touch Sensor and I2C Wire Library

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Hello All!


I'm having trouble achieving I2C communication with Sparkfun's MPR121 I2C capacitive touch sensor breakout board.  


I've used the breakout board (and code) many times before with the Arduino, but for some reason I can't get it to work with the MSP430G2553 and Energia.  


I'm using an MPR121 library found at http://bildr.org/2011/05/mpr121_arduino/  to help with register configuration.


My code compiles fine, but I'm trying to print the output from the touch sensor to the serial monitor and nothing is showing up, so I'm assuming the touch sensor isn't working.


I know the serial monitor works fine; I ran the DigitalReadSerial example and I can see the output on the monitor.  


I've connected the MPR121's SDA to pin 1.7 and the SCL to pin 1.6, and the IRQ (interrupt request) to pin 2.4.  The SDA and SCL both have 10K pull up resistors on the MPR121's breakout board.


The MPR121 is connected to Vcc and GND on the launchpad.  


Here is my code:



#include <mpr121.h>
#include <Wire.h>
boolean touchStates[12]; //to keep track of the previous touch states
void setup(){
 pinMode(P2_4, INPUT);  //  IRQ pin
 digitalWrite(P2_4, HIGH); //enable pullup resistor
void loop(){
void readTouchInputs0(){
  //read the touch state from the MPR121
  byte LSB0 = Wire.read();
  byte MSB0 = Wire.read();
  uint16_t touched = ((MSB0 << 8) | LSB0); //16bits that make up the touch states
  for (int i=0; i < 12; i++){ // Check what electrodes were pressed
   if(touched & (1<<i)){
    if(touchStates == 0){
     //pin i was just touched
     Serial.print("pin ");
     Serial.println(" was just touched");
    }else if(touchStates == 1){
     //pin i is still being touched
    touchStates = 1;   
    if(touchStates == 1){
     Serial.print("pin ");
     Serial.println(" is no longer being touched");
     //pin i is no longer being touched
    touchStates = 0;
void mpr121_setup(void){
 set_register(0x5A, ELE_CFG, 0x00); 
 // Section A - Controls filtering when data is > baseline.
 set_register(0x5A, MHD_R, 0x01);
 set_register(0x5A, NHD_R, 0x01);
 set_register(0x5A, NCL_R, 0x00);
 set_register(0x5A, FDL_R, 0x00);
 // Section B - Controls filtering when data is < baseline.
 set_register(0x5A, MHD_F, 0x01);
 set_register(0x5A, NHD_F, 0x01);
 set_register(0x5A, NCL_F, 0xFF);
 set_register(0x5A, FDL_F, 0x02);
 // Section C - Sets touch and release thresholds for each electrode
 set_register(0x5A, ELE0_T, TOU_THRESH);
 set_register(0x5A, ELE0_R, REL_THRESH);
 set_register(0x5A, ELE1_T, TOU_THRESH);
 set_register(0x5A, ELE1_R, REL_THRESH);
 set_register(0x5A, ELE2_T, TOU_THRESH);
 set_register(0x5A, ELE2_R, REL_THRESH);
 set_register(0x5A, ELE3_T, TOU_THRESH);
 set_register(0x5A, ELE3_R, REL_THRESH);
 set_register(0x5A, ELE4_T, TOU_THRESH);
 set_register(0x5A, ELE4_R, REL_THRESH);
 set_register(0x5A, ELE5_T, TOU_THRESH);
 set_register(0x5A, ELE5_R, REL_THRESH);
 set_register(0x5A, ELE6_T, TOU_THRESH);
 set_register(0x5A, ELE6_R, REL_THRESH);
 set_register(0x5A, ELE7_T, TOU_THRESH);
 set_register(0x5A, ELE7_R, REL_THRESH);
 set_register(0x5A, ELE8_T, TOU_THRESH);
 set_register(0x5A, ELE8_R, REL_THRESH);
 set_register(0x5A, ELE9_T, TOU_THRESH);
 set_register(0x5A, ELE9_R, REL_THRESH);
 set_register(0x5A, ELE10_T, TOU_THRESH);
 set_register(0x5A, ELE10_R, REL_THRESH);
 set_register(0x5A, ELE11_T, TOU_THRESH);
 set_register(0x5A, ELE11_R, REL_THRESH);
 // Section D
 // Set the Filter Configuration
 // Set ESI2
 set_register(0x5A, FIL_CFG, 0x04);
 // Section E
 // Electrode Configuration
 // Set ELE_CFG to 0x00 to return to standby mode
 set_register(0x5A, ELE_CFG, 0x0C); // Enables all 12 Electrodes
 // Section F
 // Enable Auto Config and auto Reconfig
 /*set_register(0x5A, ATO_CFG0, 0x0B);
 set_register(0x5A, ATO_CFGU, 0xC9); // USL = (Vdd-0.7)/vdd*256 = 0xC9 @3.3V  set_register(0x5A, ATO_CFGL, 0x82); // LSL = 0.65*USL = 0x82 @3.3V
 set_register(0x5A, ATO_CFGT, 0xB5);*/ // Target = 0.9*USL = 0xB5 @3.3V
 set_register(0x5A, ELE_CFG, 0x0C);
boolean checkInterrupt1(void){
 return digitalRead(P2_4);
void set_register(int address, unsigned char r, unsigned char v){
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  • 5 years later...

Hey mate, hope you are doing well. I came across your post having problems with I2C communication in other boards different from Arduino, I have the same problems, I can't make the code work for Easy8051A board, if there's any chance that you see this comment please reply or contact me at https://www.facebook.com/liri15 or qlirimmurati@gmail.com, I know that i'm asking too much but this is for an important project and i'm really hopeless right now. 

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