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