Sample program to obtain a humidity from DS2438

get_humid.c

//Sample program to obtain a humidity from DS2438
//more info:
//https://skyboo.net/2017/03/ds2438-based-1-wire-humidity-sensor/
//compile with: gcc -o humid get_humid.c

#include <stdio.h>

void get_humidity()
{
  FILE *fp;
  float temp=0, vdd=0, vad=0, humid;

  fp = fopen("/sys/bus/w1/devices/26-0000020df12e/temperature", "r");
  if (!fp)
    return;
  fscanf(fp, "%f", &temp);
  fclose(fp);

  fp = fopen("/sys/bus/w1/devices/26-0000020df12e/vdd", "r");
  if (!fp)
    return;
  fscanf(fp, "%f", &vdd);
  fclose(fp);

  fp = fopen("/sys/bus/w1/devices/26-0000020df12e/vad", "r");
  if (!fp)
    return;
  fscanf(fp, "%f", &vad);
  fclose(fp);

  temp /= 256;
  vdd /= 100;
  vad /= 100;

  if (temp==0 || vdd==0 || vad==0)
    return;

  humid = (vad / vdd - 0.16) / 0.0062 / (1.0546 - 0.00216 * temp);
  printf("humidity = %f %%RH\n", humid);
}

int main()
{
  get_humidity();
}