The rht03.c C program is a driver for the MaxDetect series RHT03 sensor, designed to run on a Raspberry Pi device, and it continuously reads and displays temperature and humidity values from the sensor. The program is distributed under the GNU Lesser General Public License (LGPL) version 3 or later, written by Gordon Henderson and part of the wiringPi project.

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/*
 * rht03.c:
 *      Driver for the MaxDetect series sensors
 *
 * Copyright (c) 2012-2013 Gordon Henderson. <projects@drogon.net>
 ***********************************************************************
 * This file is part of wiringPi:
 *      https://projects.drogon.net/raspberry-pi/wiringpi/
 *
 *    wiringPi is free software: you can redistribute it and/or modify
 *    it under the terms of the GNU Lesser General Public License as published b                                                                                                             y
 *    the Free Software Foundation, either version 3 of the License, or
 *    (at your option) any later version.
 *
 *    wiringPi is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU Lesser General Public License for more details.
 *
 *    You should have received a copy of the GNU Lesser General Public License
 *    along with wiringPi.  If not, see <http://www.gnu.org/licenses/>.
 ***********************************************************************
 */

#include <stdio.h>
#include <time.h>

#include <wiringPi.h>
#include <maxdetect.h>

#define RHT03_PIN       7

/*
 ***********************************************************************
 * The main program
 ***********************************************************************
 */

int main (void)
{
  int temp, rh ;
  float  temp2 ;
  int newTemp, newRh ;

  temp = rh = newTemp = newRh = 0 ;

  wiringPiSetup () ;
  piHiPri       (55) ;

  for(;;)
  {

    if (!readRHT03 (RHT03_PIN, &newTemp, &newRh))
    {
      delay(57);
      continue;
    }

    if ((temp != newTemp) || (rh != newRh))
    {
      temp = newTemp ;
      temp2 = (9.0 / 5) * (newTemp / 10) + 32;
      rh   = newRh ;
      fprintf (stdout, "celsius=%.2f&fahrenheit=%.2f&humidity=%.2f&time=%u\n", temp / 10.0, temp2, rh / 10.0, (unsigned)time(NULL)) ;
      fflush(stdout);
    }

    delay(23000);
  }

  return 0 ;
}

/**
 * @file rht03.c
 * @brief Driver for the MaxDetect series sensors
 *
 * @copyright 2012-2013 Gordon Henderson 
 *
 * @note This file is part of wiringPi:
 *       https://projects.drogon.net/raspberry-pi/wiringpi/
 */

#include 
#include 
#include 
#include 

#define RHT03_PIN       7
#define DELAY_MS        23000
#define SERIAL_DELAY_MS 57

#define MAX_TEMPERATURE 100
#define MAX_HUMIDITY    100

/**
 * @brief Setup function for wiringPi
 */
void setup(void) {
    wiringPiSetup();
    piHiPri(55);
}

/**
 * @brief Main program loop
 */
void loop(void) {
    int newTemp, newRh;
    float temp2;

    if (readRHT03(RHT03_PIN, &newTemp, &newRh)) {
        if ((temp!= newTemp) || (rh!= newRh)) {
            temp = newTemp;
            temp2 = (9.0 / 5) * (newTemp / 10) + 32;
            rh = newRh;
            printf("celsius=%.2f&fahrenheit=%.2f&humidity=%.2f&time=%u\n", temp / 10.0, temp2, rh / 10.0, (unsigned)time(NULL));
            fflush(stdout);
        }
    } else {
        // Serial interface is not available, wait and try again
        usleep(SERIAL_DELAY_MS * 1000);
    }

    usleep(DELAY_MS * 1000);
}

int main(void) {
    int temp, rh;
    float temp2;

    temp = rh = 0;
    setup();

    while (1) {
        loop();
    }

    return 0;
}

File Overview

This is a C program named rht03.c that serves as a driver for the MaxDetect series sensors, specifically the RHT03 sensor. The program is designed to run on a Raspberry Pi device.

Includes and Definitions

The program includes the following header files:

• stdio.h: for standard input/output operations
• time.h: for time-related functions
• wiringPi.h: for wiringPi library functions
• maxdetect.h: for MaxDetect sensor library functions

The program defines a single constant:

• RHT03_PIN: the pin number on the Raspberry Pi where the RHT03 sensor is connected (pin 7)

Main Program

The main function is the entry point of the program. It performs the following tasks:

1. Initializes variables to store temperature, humidity, and new temperature/humidity values.
2. Sets up the wiringPi library using wiringPiSetup.
3. Sets the priority of the program to 55 using piHiPri.
4. Enters an infinite loop where it:
   • Reads the temperature and humidity values from the RHT03 sensor using readRHT03.
   • Checks if the new values are different from the previous ones.
   • If the values are different, updates the temperature and humidity variables and prints the values to the console using fprintf. The output format includes the temperature in Celsius and Fahrenheit, humidity, and the current time.
   • Waits for 57 milliseconds using delay(57) if an error occurs while reading the sensor values.
   • Waits for 23 seconds using delay(23000).

License and Copyright

The program is distributed under the GNU Lesser General Public License (LGPL) version 3 or later. The copyright notice indicates that the program was written by Gordon Henderson and is part of the wiringPi project.