MPR121 seems like it freezes

[kinna]

Hi

I have a problem with the MPR121 Capacitive Touch Sensor Controller. I configured it as recommended in the Quick Start Guide and most of the time it works very well. I have only three electrodes connected and it responds nicely when I touch one and then releases. But if I touch all of them at once or quickly move my finger from one to another, it seems like it freezes. If I re-initialize the MPR121 it works again, but freezes again if I touch all the electrodes or quickly move my finger. 

I have checked that it is not the microcontroller, everything else is still running.

Does anyone know what I might have done wrong?

The configuration settings are shown here:

// Enter stop mode (for re-initialization)

  touch_set(0x5E,0x00);

  // Recommended filter settings when electrode data > baseline value

  // (rising)

  touch_set(0x2B,0x01);

  touch_set(0x2C,0x01);

  touch_set(0x2D,0x00);

  touch_set(0x2E,0x00);

  // Recommended filter settings when electrode data < baseline value

  // (falling)

  touch_set(0x2F,0x01);

  touch_set(0x30,0x01);

  touch_set(0x31,0xFF);

  touch_set(0x32,0x02);

  // Setting touch- and release thresholds for electrode 0

  touch_set(0x41,0x0F);

  touch_set(0x42,0x0A);

  // Setting touch- and release thresholds for electrode 1

  touch_set(0x43,0x0F);

  touch_set(0x44,0x0A);

  // Setting touch- and release thresholds for electrode 2

  touch_set(0x45,0x0F);

  touch_set(0x46,0x0A);

  // Setting sample rate to 1ms

  touch_set(0x5D,0x04);

  // Enable auto config and auto reconfig

  touch_set(0x7B,0x0B);

  touch_set(0x7D,0x9C);

  touch_set(0x7E,0x65);

  touch_set(0x7F,0x8C);

  // Enable touch on electrode 0-2 - this also enables the controller and

  // must be set as the last

  touch_set(0x5E,0x3);

[reyes]

You should probably test it again using the following configuration:

#define TouchThre 10   //15//30//10

#define ReleaThre 6   //8//25//8

void MPR121_init(void)

{

  //Reset MPR121 if not reset correctly

  IIC_ByteWrite(0x80,0x63);  //Soft reset 

  IIC_ByteWrite(0x5E,0x00);  //Stop mode  

  //touch pad baseline filter

  //rising                                    

  IIC_ByteWrite(0x2B,0x01); // MAX HALF DELTA Rising

  IIC_ByteWrite(0x2C,0x01); // NOISE HALF DELTA Rising

  IIC_ByteWrite(0x2D,0x0E); // NOISE COUNT LIMIT Rising

  IIC_ByteWrite(0x2E,0x00); // DELAY LIMIT Rising

  //falling

  IIC_ByteWrite(0x2F,0x01); // MAX HALF DELTA Falling

  IIC_ByteWrite(0x30,0x05); // NOISE HALF DELTA Falling

  IIC_ByteWrite(0x31,0x01); // NOISE COUNT LIMIT Falling

  IIC_ByteWrite(0x32,0x00); // DELAY LIMIT Falling

  //touched

  IIC_ByteWrite(0x33,0x00); // Noise half delta touched

  IIC_ByteWrite(0x34,0x00); // Noise counts touched

  IIC_ByteWrite(0x35,0x00); // Filter delay touched

  //Touch pad threshold

  IIC_ByteWrite(0x41,TouchThre); // ELE0 TOUCH THRESHOLD

  IIC_ByteWrite(0x42,ReleaThre); // ELE0 RELEASE THRESHOLD

  IIC_ByteWrite(0x43,TouchThre); // ELE1 TOUCH THRESHOLD

  IIC_ByteWrite(0x44,ReleaThre); // ELE1 RELEASE THRESHOLD

  IIC_ByteWrite(0x45,TouchThre); // ELE2 TOUCH THRESHOLD

  IIC_ByteWrite(0x46,ReleaThre); // ELE2 RELEASE THRESHOLD

  //touch /release debounce

  IIC_ByteWrite(0x5B,0x00);

  // response time = SFI(10) X ESI(8ms) = 80ms

  IIC_ByteWrite(0x5D,0x13);    

  //FFI=18 

  IIC_ByteWrite(0x5C,0x80);  

  //Auto configuration

  IIC_ByteWrite(0x7B,0x8F); 

  // charge to 70% of Vdd , high sensitivity 

  IIC_ByteWrite(0x7D,0xE4);

  IIC_ByteWrite(0x7E,0x94);

  IIC_ByteWrite(0x7F,0xCD);

  //3 electrodes enabled    

  IIC_ByteWrite(0x5E,0x03);  

}

Let me know if you still have problems after this.

[kinna]

Thanks for your reply. I tried the configuration you wrote, but it still freezes when I move my fingers fast from one electrode to another.

I'm using an ATmega 328P as master with this setup:

void twi_master_init()

{

  // Set prescaler value to 1

  TWSR &= ~(1 << TWPS1) & ~(1 << TWPS0);

  // Set Bit Rate Register to 2 (clock division factor)

  TWBR = 0x2;

}

Could that have something to do with it?

[reyes]

It’s possible that the problem its timing related (it’s possible that you are not running at the 400 kHz needed for the MPR121).

But you can find a code example for the MPR121 using the ATmega328 on the link below, I would recommend you to test your MPR121 using the code on this link: https://www.sparkfun.com/products/9695