分类： Funny

MPR121 是一款触摸传感器芯片，原理是通过检测电容变化来判断当前是否有触摸（接近）。

主要电器特性如下【参考1】：
1. 工作电压1.71-3.6v(芯片工作电压)
2. 通讯接口为 I2C
3. 12个检测端口
4. 带有1个 IRQ端口

我是在Taobao购买的模块，价格是16元【参考3】。经过搜索，这是仿sparkfun的，更多资料可以在【参考2】看到。

模块长得下面这样，有一个降压芯片，看起来可以直接使用 5V 供电。上面有12个口，可以接12个触摸按钮。IRQ 的作用是发出中断通知上面有触摸。ADD是芯片的I2C地址选择，接GND VDD SDA或者 SCL 地址分别是 0x5A 0x5B 0x5C 和 0x5D【来自参考4】。

图片来自【参考2】

下面的代码可以正常工作（卖家的例程，有一些修改可以在 1.6.0 上编译通过）

#include "mpr121.h"
#include <Wire.h>

#define SENSORS       13
#define TOU_THRESH    0x1F
#define REL_THRESH    0x1A
#define PROX_THRESH   0x3f
#define PREL_THRESH   0x3c

// variables: capacitive sensing
bool touchStates[SENSORS];    // holds the current touch/prox state of all sensors
bool activeSensors[SENSORS] = {1,1,1,1,1,1,1,1,1,1,1,1,1}; // holds which sensors are active (0=inactive, 1=active)
bool newData = false;         // flag that is set to true when new data is available from capacitive sensor
int irqpin = 2;               // pin that connects to notifies when data is available from capacitive sensor

void setup(){

  // attach interrupt to pin - interrupt 1 is on pin 2 of the arduino (confusing I know)
  attachInterrupt(0, dataAvailable, FALLING);

  // set-up the Serial and I2C/Wire connections
  Serial.begin(9600);
  Wire.begin();

  // set the registers on the capacitive sensing IC
  setupCapacitiveRegisters();

}

void loop(){
  readCapacitiveSensor();
}

/**
 * dataAvailable Callback method that runs whenever new data becomes available on from the capacitive sensor. 
 *   This method was attached to the interrupt on pin 2, and is called whenever that pins goes low.
 */
void dataAvailable() {
  newData = true;
}

/**
 * readCapacitiveSensor Reads the capacitive sensor values from the MP121 IC. It makes a request to
 *   the sensor chip via the I2C/Wire connection, and then parses the sensor values which are stored on
 *   the first 13 bits of the 16-bit response msg.
 */
void readCapacitiveSensor(){
  if(newData){    
            Serial.println("yes");      
    //read the touch state from the MPR121
    Wire.requestFrom(0x5A,2); 
    byte tLSB = Wire.read();
    byte tMSB = Wire.read();
    uint16_t touched = ((tMSB << 8) | tLSB); //16bits that make up the touch states

    for (int i = 0; i < SENSORS; i++){  // Check what electrodes were pressed
      if (activeSensors[i] == 0) continue;
      char sensor_id [] = {'\0','\0','\0'};
      switch (i) {
        case 12:
          sensor_id[0] = 'P';
          break;
        default:
          if (i < 10) {
            sensor_id[0] = char( i+48 );
          } 
          else if (i < 12) {
            sensor_id[0] = char('1');
            sensor_id[1] = char( ( i % 10 ) + 48 );
          } 
      }
      if (sensor_id != '\0') {
        // read the humidity level

        // if current sensor was touched (check appropriate bit on touched var)
        if(touched & (1<<i)){      
          // if current pin was not previously touched send a serial message
          if(touchStates[i] == 0){          
            Serial.print(sensor_id);        
            Serial.print(":");
            Serial.println("1");
          } 
          touchStates[i] = 1;      
        } else {
          // if current pin was just touched send serial message
          if(touchStates[i] == 1){
            Serial.print(sensor_id);
            Serial.print(":");
            Serial.println("0");
          }
          touchStates[i] = 0;
        }        
      }
    }
    newData = false;
  }
}

/**
 * setupCapacitiveRegisters Updates all of configurations on the MP121 capacitive sensing IC. This includes
 *   setting levels for all filters, touch and proximity sensing activation and release thresholds, debounce,
 *   and auto-configurations options. At the end it activates all of the electrodes.
 */
void setupCapacitiveRegisters(){

  set_register(0x5A, ELE_CFG, 0x00); 
  
  // Section A - filtering when data is > baseline.
    // touch sensing
    set_register(0x5A, MHD_R, 0x01);
    set_register(0x5A, NHD_R, 0x01);
    set_register(0x5A, NCL_R, 0x00);
    set_register(0x5A, FDL_R, 0x00);

    // prox sensing 
    set_register(0x5A, PROX_MHDR, 0xFF);
    set_register(0x5A, PROX_NHDAR, 0xFF);
    set_register(0x5A, PROX_NCLR, 0x00);
    set_register(0x5A, PROX_FDLR, 0x00);

  // Section B - filtering when data is < baseline.
    // touch sensing
    set_register(0x5A, MHD_F, 0x01);
    set_register(0x5A, NHD_F, 0x01);
    set_register(0x5A, NCL_F, 0xFF);
    set_register(0x5A, FDL_F, 0x02);
  
    // prox sensing
    set_register(0x5A, PROX_MHDF, 0x01);
    set_register(0x5A, PROX_NHDAF, 0x01);
    set_register(0x5A, PROX_NCLF, 0xFF);
    set_register(0x5A, PROX_NDLF, 0xFF);

  // 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 touch filter Configuration
    set_register(0x5A, FIL_CFG, 0x04);  

  // Section E - Set proximity sensing threshold and release
    set_register(0x5A, PRO_T, PROX_THRESH);   // sets the proximity sensor threshold
    set_register(0x5A, PRO_R, PREL_THRESH);   // sets the proximity sensor release

  // Section F - Set proximity sensor debounce
    set_register(0x59, PROX_DEB, 0x50);  // PROX debounce

  // Section G - Set Auto Config and Auto Reconfig for prox sensing
    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, ATO_CFG0, 0x0B);

  // Section H - Start listening to all electrodes and the proximity sensor
    set_register(0x5A, ELE_CFG, 0x3C);
}

/**
 * set_register Sets a register on a device connected via I2C. It accepts the device's address, 
 *   register location, and the register value.
 * @param address The address of the I2C device
 * @param r       The register's address on the I2C device
 * @param v       The new value for the register
 */
void set_register(int address, unsigned char r, unsigned char v){
  Wire.beginTransmission(address);
  Wire.write(r);
  Wire.write(v);
  Wire.endTransmission();
}

运行结果：

完整的代码下载

MPR121

参考：
1. http://wenku.baidu.com/link?url=77EtEpflHOBF9LmqwOvIwe5ONZ6I548h4BcBk4Ep1XWVO_RVDj9fycwoku44RENseV48lzvnrnDasY3UAMHsBuuU7yVdxFsAfxq-zbDiEhy MPR121中文数据手册
2. https://learn.sparkfun.com/tutorials/mpr121-hookup-guide
3. https://item.taobao.com/item.htm?spm=a1z09.2.0.0.kpoNRc&id=19968128319&_u=pkf8s90f4c
4. MPR121 DataSheet

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额外说一下这个传感器在 Pro Micro 上的连接方法：

1. Pro Micro 的中断：“The Pro Micro has five external interrupts, which allow you to instantly trigger a function when a pin goes either high or low (or both). If you attach an interrupt to an interrupt-enabled pin, you’ll need to know the specific interrupt that pin triggers: pin 3 maps to interrupt 0, pin 2 is interrupt 1, pin 0 is interrupt 2, pin 1 is interrupt 3, and pin 7 is interrupt 4.”
推荐 使用 Pin7-Interrupt 4
2. Pro Micro Pin2- SDA Pin3-SCL