144 lines
5.2 KiB
C
144 lines
5.2 KiB
C
/*
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* Part of esp-open-rtos
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* Copyright (C) 2016 Jonathan Hartsuiker (https://github.com/jsuiker)
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* BSD Licensed as described in the file LICENSE
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*
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*/
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#include "dht.h"
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#include "string.h"
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#include "task.h"
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#include "esp/gpio.h"
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#include <espressif/esp_misc.h> // sdk_os_delay_us
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#ifndef DEBUG_DHT
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#define DEBUG_DHT 0
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#endif
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#if DEBUG_DHT
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#define debug(fmt, ...) printf("%s" fmt "\n", "dht: ", ## __VA_ARGS__);
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#else
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#define debug(fmt, ...) /* (do nothing) */
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#endif
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/*
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* Note:
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* A suitable pull-up resistor should be connected to the selected GPIO line
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*
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* __ ______ _______ ___________________________
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* \ A / \ C / \ DHT duration_data_low / \
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* \_______/ B \______/ D \__________________________/ DHT duration_data_high \__
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*
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*
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* Initializing communications with the DHT requires four 'phases' as follows:
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*
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* Phase A - MCU pulls signal low for at least 18000 us
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* Phase B - MCU allows signal to float back up and waits 20-40us for DHT to pull it low
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* Phase C - DHT pulls signal low for ~80us
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* Phase D - DHT lets signal float back up for ~80us
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*
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* After this, the DHT transmits its first bit by holding the signal low for 50us
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* and then letting it float back high for a period of time that depends on the data bit.
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* duration_data_high is shorter than 50us for a logic '0' and longer than 50us for logic '1'.
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*
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* There are a total of 40 data bits trasnmitted sequentially. These bits are read into a byte array
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* of length 5. The first and third bytes are humidity (%) and temperature (C), respectively. Bytes 2 and 4
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* are zero-filled and the fifth is a checksum such that:
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*
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* byte_5 == (byte_1 + byte_2 + byte_3 + btye_4) & 0xFF
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*
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*/
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/*
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* @pin the selected GPIO pin
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* @interval how frequently the pin state is checked in microseconds
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* @timeout maximum length of time to wait for the expected pin state
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* @expected_pin_state high (true) or low (false) pin state
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* @counter pointer to external uint8_t for tallying the duration waited for the pin state
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*/
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bool dht_await_pin_state(uint8_t pin, uint8_t interval, uint8_t timeout, bool expected_pin_state, uint8_t * counter) {
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for (*counter = 0; *counter < timeout; *counter+=interval) {
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if (gpio_read(pin) == expected_pin_state) return true;
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sdk_os_delay_us(interval);
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}
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return false;
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}
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/*
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*
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*
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* @pin the selected GPIO pin
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* @humidity pointer to external int8_t to store resulting humidity value
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* @temperature pointer to external int8_t to store resulting temperature value
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*/
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bool dht_fetch_data(int8_t pin, int8_t * humidity, int8_t * temperature) {
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int8_t data[40] = {0};
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int8_t result[5] = {0};
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uint8_t i = 0;
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uint8_t init_phase_duration = 0;
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uint8_t duration_data_low = 0;
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uint8_t duration_data_high = 0;
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gpio_enable(pin, GPIO_OUT_OPEN_DRAIN);
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taskENTER_CRITICAL();
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// Phase 'A' pulling signal low to initiate read sequence
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gpio_write(pin, 0);
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sdk_os_delay_us(20000);
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gpio_write(pin, 1);
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// Step through Phase 'B' at 2us intervals, 40us max
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if (dht_await_pin_state(pin, 2, 40, false, &init_phase_duration)) {
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// Step through Phase 'C ' at 2us intervals, 88us max
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if (dht_await_pin_state(pin, 2, 88, true, &init_phase_duration)) {
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// Step through Phase 'D' at 2us intervals, 88us max
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if (dht_await_pin_state(pin, 2, 88, false, &init_phase_duration)) {
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// Read in each of the 40 bits of data...
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for (i = 0; i < 40; i++) {
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if (dht_await_pin_state(pin, 2, 60, true, &duration_data_low)) {
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if (dht_await_pin_state(pin, 2, 75, false, &duration_data_high)) {
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data[i] = duration_data_high > duration_data_low;
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}
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}
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}
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taskEXIT_CRITICAL();
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for (i = 0; i < 40; i++) {
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// Read each bit into 'result' byte array...
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result[i/8] <<= 1;
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result[i/8] |= data[i];
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}
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if (result[4] == ((result[0] + result[1] + result[2] + result[3]) & 0xFF)) {
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// Data valid, checksum succeeded...
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*humidity = result[0];
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*temperature = result[2];
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debug("Successfully retrieved sensor data...");
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return true;
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} else {
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debug("Checksum failed, invalid data received from sensor...");
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}
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} else {
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debug("Initialization error, problem in phase 'D'...");
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}
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} else {
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debug("Initialization error, problem in phase 'C'...");
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}
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} else {
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debug("Initialization error, problem in phase 'B'...");
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}
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taskEXIT_CRITICAL();
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return false;
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}
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