Hello, I'm new to these forums so I hope I'm posting this question in the right place. I have a question about a project I'm doing that uses the chip mptr121. Basically the project is just a flat electrode that senses how hard a finger is pressed against it, and I would like to know if this project is possible. I have done a succesful test with the chip before, by wiring it to an arduino with the attached diagram 1. In this diagram, there is the i2c pins connected to the arduino, the interupt pin is 12, and There are power and ground pins connected too. Also, each output of the mpr121 is connected to a different electrode. Each time a electrode is touched or released, I can see a print on the serial monitor letting me know witch electrode was pushed or released. Here is the code I used:
#include "mpr121.h"
#include <Wire.h>
#include <SPI.h>
#include <SD.h>
int irqpin = 12; // Digital 2
int SDApin = 19;
int SCLpin = 18;
boolean touchStates[12]; //to keep track of the previous touch states
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 checkInterrupt(void){
return digitalRead(irqpin);
}
void set_register(int address, unsigned char r, unsigned char v){
Wire.beginTransmission(address);
Wire.write(r);
Wire.write(v);
Wire.endTransmission();
}
void setup(){
Serial.begin(9600);
pinMode(irqpin, INPUT);
digitalWrite(irqpin, HIGH); //enable pullup resistor
Wire.begin();
mpr121_setup();
}
void loop(){
readTouchInputs();
for(int i = 0; i < 12; i++){
if(touchStates[i]){
} else {
}
}
}
void readTouchInputs(){
if(!checkInterrupt()){
//read the touch state from the MPR121
Wire.requestFrom(0x5A,2);
byte LSB = Wire.read();
byte MSB = Wire.read();
uint16_t touched = ((MSB << 8) | LSB); //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[i] == 0){
//pin i was just touched
Serial.print("pin ");
Serial.print(i);
Serial.println(" was just touched");
touchStates[i] = 0;
}
}
}
}
}
mpr.h can be found here: MPR121_Capacitive_Touch_Breakout/mpr121.h at master · sparkfun/MPR121_Capacitive_Touch_Breakout · GitHub
So now I tried wiring the electrodes differently to try out my idea. I shorted all the inputs into one electrode, and uploaded the following code:
#include "mpr121.h"
#include <Wire.h>
#include <SPI.h>
#include <SD.h>
int irqpin = 12; // Digital 2
int SDApin = 19;
int SCLpin = 18;
boolean touchStates[12]; //to keep track of the previous touch states
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
for(int i = 0; i< 24; i++){
set_register(0x5A, ELE0_T+i, TOU_THRESH+4*i);
i++;
set_register(0x5A, ELE0_T+i, REL_THRESH+4*i);
}
// 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 checkInterrupt(void){
return digitalRead(irqpin);
}
void set_register(int address, unsigned char r, unsigned char v){
Wire.beginTransmission(address);
Wire.write(r);
Wire.write(v);
Wire.endTransmission();
}
void setup(){
Serial.begin(9600);
pinMode(irqpin, INPUT);
digitalWrite(irqpin, HIGH); //enable pullup resistor
Wire.begin();
mpr121_setup();
}
void loop(){
readTouchInputs();
for(int i = 0; i < 12; i++){
if(touchStates[i]){
} else {
}
}
}
void readTouchInputs(){
if(!checkInterrupt()){
//read the touch state from the MPR121
Wire.requestFrom(0x5A,2);
byte LSB = Wire.read();
byte MSB = Wire.read();
uint16_t touched = ((MSB << 8) | LSB); //16bits that make up the touch states
Serial.println(touched);
for (int i=0; i < 12; i++){ // Check what electrodes were pressed
if(touched & (1<<i)){
if(touchStates[i] == 0){
//pin i was just touched
Serial.print("pin ");
Serial.print(i);
Serial.println(" was just touched");
touchStates[i] = 0;
}
}
}
}
}
And mpr.h unchanged. My goal with this sketch is to detect the intesity that someone is pushing against the electrode. There are 12 different levels of intensity that can be detected, but the code doesn't work, and nothing is printed on the monitor. I would apreciate any guidance that you guys can offer me to acheive my objective, Thanks.
