AVR Freaks

Why is the library function (not) returning -1?

Does this mean that the DHT is returning an integer value instead of float?

dht.c:

/*
DHT Library 0x03

copyright (c) Davide Gironi, 2012

Released under GPLv3.
Please refer to LICENSE file for licensing information.
*/


#include <stdio.h>
#include <string.h>
#include <avr/io.h>
#include <util/delay.h>

#include "dht.h"

/*
 * get data from sensor
 */
#if DHT_FLOAT == 1
int8_t dht_getdata(float *temperature, float *humidity) {
#elif DHT_FLOAT == 0
int8_t dht_getdata(int8_t *temperature, int8_t *humidity) {
#endif
	uint8_t bits[5];
	uint8_t i,j = 0;

	memset(bits, 0, sizeof(bits));

	//reset port
	DHT_DDR |= (1<<DHT_INPUTPIN); //output
	DHT_PORT |= (1<<DHT_INPUTPIN); //high
	_delay_ms(100);

	//send request
	DHT_PORT &= ~(1<<DHT_INPUTPIN); //low
	#if DHT_TYPE == DHT_DHT11
	_delay_ms(18);
	#elif DHT_TYPE == DHT_DHT22
	_delay_us(500);
	#endif
	DHT_PORT |= (1<<DHT_INPUTPIN); //high
	DHT_DDR &= ~(1<<DHT_INPUTPIN); //input
	_delay_us(40);

	//check start condition 1
	if((DHT_PIN & (1<<DHT_INPUTPIN))) {
		return -1;
	}
	_delay_us(80);
	//check start condition 2
	if(!(DHT_PIN & (1<<DHT_INPUTPIN))) {
		return -1;
	}
	_delay_us(80);

	//read the data
	uint16_t timeoutcounter = 0;
	for (j=0; j<5; j++) { //read 5 byte
		uint8_t result=0;
		for(i=0; i<8; i++) {//read every bit
			timeoutcounter = 0;
			while(!(DHT_PIN & (1<<DHT_INPUTPIN))) { //wait for an high input (non blocking)
				timeoutcounter++;
				if(timeoutcounter > DHT_TIMEOUT) {
					return -1; //timeout
				}
			}
			_delay_us(30);
			if(DHT_PIN & (1<<DHT_INPUTPIN)) //if input is high after 30 us, get result
				result |= (1<<(7-i));
			timeoutcounter = 0;
			while(DHT_PIN & (1<<DHT_INPUTPIN)) { //wait until input get low (non blocking)
				timeoutcounter++;
				if(timeoutcounter > DHT_TIMEOUT) {
					return -1; //timeout
				}
			}
		}
		bits[j] = result;
	}

	//reset port
	DHT_DDR |= (1<<DHT_INPUTPIN); //output
	DHT_PORT |= (1<<DHT_INPUTPIN); //low
	_delay_ms(100);

	//check checksum
	if ((uint8_t)(bits[0] + bits[1] + bits[2] + bits[3]) == bits[4]) {
		//return temperature and humidity
		#if DHT_TYPE == DHT_DHT11
		*temperature = bits[2];
		*humidity = bits[0];
		#elif DHT_TYPE == DHT_DHT22
		uint16_t rawhumidity = bits[0]<<8 | bits[1];
		uint16_t rawtemperature = bits[2]<<8 | bits[3];
		if(rawtemperature & 0x8000) {
			*temperature = (float)((rawtemperature & 0x7FFF) / 10.0) * -1.0;
		} else {
			*temperature = (float)(rawtemperature)/10.0;
		}
		*humidity = (float)(rawhumidity)/10.0;
		#endif
		return 0;
	}

	return -1;
}

/*
 * get temperature
 */
#if DHT_FLOAT == 1
int8_t dht_gettemperature(float *temperature) {
	float humidity = 0;
#elif DHT_FLOAT == 0
int8_t dht_gettemperature(int8_t *temperature) {
	int8_t humidity = 0;
#endif
	return dht_getdata(temperature, &humidity);
}

/*
 * get humidity
 */
#if DHT_FLOAT == 1
int8_t dht_gethumidity(float *humidity) {
	float temperature = 0;
#elif DHT_FLOAT == 0
int8_t dht_gethumidity(int8_t *humidity) {
	int8_t temperature = 0;
#endif
	return dht_getdata(&temperature, humidity);
}

/*
 * get temperature and humidity
 */
#if DHT_FLOAT == 1
int8_t dht_gettemperaturehumidity(float *temperature, float *humidity) {
#elif DHT_FLOAT == 0
	int8_t dht_gettemperaturehumidity(int8_t *temperature, int8_t *humidity) {
#endif
	return dht_getdata(temperature, humidity);
}

dht.h

/*
DHT Library 0x03

copyright (c) Davide Gironi, 2012

Released under GPLv3.
Please refer to LICENSE file for licensing information.

References:
  - DHT-11 Library, by Charalampos Andrianakis on 18/12/11
*/


#ifndef DHT_H_
#define DHT_H_

#include <stdio.h>
#include <avr/io.h>

//setup port
#define DHT_DDR DDRD
#define DHT_PORT PORTD
#define DHT_PIN PIND
#define DHT_INPUTPIN PD6

//sensor type
#define DHT_DHT11 1
#define DHT_DHT22 2
#define DHT_TYPE DHT_DHT22

//enable decimal precision (float)
#if DHT_TYPE == DHT_DHT11
#define DHT_FLOAT 0
#elif DHT_TYPE == DHT_DHT22
#define DHT_FLOAT 1
#endif

//timeout retries
#define DHT_TIMEOUT 200

//functions
#if DHT_FLOAT == 1
extern int8_t dht_gettemperature(float *temperature);
extern int8_t dht_gethumidity(float *humidity);
extern int8_t dht_gettemperaturehumidity(float *temperature, float *humidity);
#elif DHT_FLOAT == 0
extern int8_t dht_gettemperature(int8_t *temperature);
extern int8_t dht_gethumidity(int8_t *humidity);
extern int8_t dht_gettemperaturehumidity(int8_t *temperature, int8_t *humidity);
#endif

#endif

Aah, thank you so much, David sir. There lies your awesomeness!

So if we change all float to int in the main C program, and keep the dht.h unchanged, would it work?

Or should I edit the dht.h?

I wrote this and it shows 0,0 as temp, humidity values.

#include <stdio.h>
#include <stdlib.h>
#define F_CPU 8000000UL
#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>


#include "dht.h"
#include "lcd.h"

int main(void)
{
	
	DHT_FLOAT == 0;
	
	char buffer[100];
	lcd_init(LCD_DISP_ON);
	sei();   //init interrupt

	int8_t temperature = 0;
	int8_t humidity = 0;
	
	_delay_ms(2000);

	
	while (1)
	
	{
		lcd_clrscr();
			
	dht_gettemperaturehumidity(&temperature, &humidity);
		
			itoa(temperature, buffer, 10);
			lcd_puts("temp: ");
			lcd_puts(buffer);
			lcd_puts("C");
			
		
			
			itoa(humidity, buffer, 10);
			lcd_puts("hum : ");
			lcd_puts(buffer);
			lcd_puts("%RH");
			
			_delay_ms(2000);
			
		}
			
		

		lcd_puts("Done");
}