Reading MCP3008 using C on the Raspberry Pi

mcp3008.c

//  Using C to read the MCP3008 10-bit
//  ADC via SPI

#include <stdio.h>
#include <bcm2835.h>

uint8_t start = 0x01;
uint8_t end = 0x00;
uint8_t chan = 0x00;

int readADC(uint8_t chan);
float volts_adc(int adc);

int readADC(uint8_t chan){
  char buf[] = {start, (0x08|chan)<<4,end};
  char readBuf[3];
  bcm2835_spi_transfernb(buf,readBuf,3);
  return ((int)readBuf[1] & 0x03) << 8 | (int) readBuf[2];
}

float volts_adc(int adc) {
  return (float)adc*3.3f/1023.0f;
}

int main(int argc, char const *argv[]) {
    if (!bcm2835_init())
    {
      printf("bcm2835_init failed. Are you running as root??\n");
      return 1;
    }

    if (!bcm2835_spi_begin())
    {
      printf("bcm2835_spi_begin failed. Are you running as root??\n");
      return 1;
    }
    bcm2835_spi_setBitOrder(BCM2835_SPI_BIT_ORDER_MSBFIRST);      // The default
    bcm2835_spi_setDataMode(BCM2835_SPI_MODE0);                   // The default
    bcm2835_spi_setClockDivider(BCM2835_SPI_CLOCK_DIVIDER_65536); // The default
    bcm2835_spi_chipSelect(BCM2835_SPI_CS0);                      // The default
    bcm2835_spi_setChipSelectPolarity(BCM2835_SPI_CS0, LOW);      // the default

    for(uint8_t i=0; i<10; i++) {
      int adc = readADC(chan);
      printf("ADC level on channel %02x is: %04x (%0.2f v)\n",chan,adc,volts_adc(adc));
    }
    
    return 0;
}