porklib: Simple library for programming Arduino in C
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avr-lib/examples/dht11/lib/dht11.c

89 lines
1.4 KiB

9 years ago
#include <avr/io.h>
#include <util/delay.h>
#include <stdint.h>
#include <stdbool.h>
#include "iopins.h"
#include "dht11.h"
/** Read one bit */
bool _dht11_rxbit(const uint8_t pin)
{
// Wait until start of pulse
while (is_low_n(pin));
uint8_t cnt = 0;
while (is_high_n(pin))
{
cnt++;
_delay_us(5);
}
return (cnt > 8);
}
/** Read one byte */
uint8_t _dht11_rxbyte(const uint8_t pin)
{
uint8_t byte = 0;
for (uint8_t i = 0; i < 8; i++)
{
if (_dht11_rxbit(pin))
byte |= (1 << (7 - i));
}
return byte;
}
/** Read tehmperature and humidity from the DHT11, returns false on failure */
bool dht11_read(const uint8_t pin, dht11_result_t* result)
{
// bus down for > 18 ms
as_output_n(pin);
pin_low_n(pin);
_delay_ms(20);
// bus up for 20-40us
pin_high_n(pin);
_delay_us(20);
// release
as_input_pu_n(pin);
// DHT should send 80us LOW & 80us HIGH
_delay_us(40);
if (!is_low_n(pin))
return false; // init error
_delay_us(80);
if (!is_high_n(pin))
return false; // init error
// skip to start of first bit
_delay_us(50);
// Receive 5 data bytes (Rh int, Rh dec, Temp int, Temp dec, Checksum)
// Decimal bytes are zero for DHT11 -> we can ignore them.
uint8_t bytes[5];
uint8_t sum = 0;
for (uint8_t i = 0; i < 5; i++)
{
uint8_t b = _dht11_rxbyte(pin);
bytes[i] = b;
if (i < 4) sum += b;
}
// Verify checksum
if (sum != bytes[4]) return false;
result->rh = bytes[0];
result->temp = bytes[2];
return true;
}