Ioannis Anastasopoulos

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7 years, 2 months ago.

MCP3421 I2C communication

Dear all,

I am trying to communicate using the NRF51822 with the MCP3421A1T using the I2C bus.

My setup is the following:

SDA_PIN is 9 SCL_PIN is 10

the pull-up resistors are 3kΩ.

My code looks is this:

include the mbed library with this snippet

#include "mbed.h"

#define SDA_PIN p9
#define SCL_PIN p10

I2C i2c(SDA_PIN, SCL_PIN);

const char addr = 0xD2;// 7bit address of the ADC (for this particular one it is 0x69) on the I2C bus shifted by 1 bit, with the R/W bit set to 0

double readADC(){
    char cmd[3];
 
    cmd[0] = 0x88;
    i2c.start();
    int t = i2c.write(addr);
    int k = i2c.write(cmd[0]);
    i2c.read( addr, cmd, 3);
    i2c.stop();
    if(k == 0){
        long t = cmd[0] << 8 |  cmd[1];
    
    if (t >= 32768) t = 65536l - t;
    
    double v = (double) t * 2.048/32768.0;

    return v;    
    }else{
        return 10.0;    
    }
}

What I get is that there is no acknowledgement from the I2C bus and what is more, even if I change the address of the device I always get the same results, which means that there something not working on this code.

What I want to do is to cpnfigure the register byte of the MCP3421 as 1001000 and then perform a reading after a one-shot measurement.

Does anybody have a clue on this ?

Thank you very much.

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