Merge pull request #129 from jsuiker/feature/dht-sensors

Added DHT library to extras and sample code to examples
This commit is contained in:
Angus Gratton 2016-04-25 14:28:01 +10:00
commit 11ec316038
5 changed files with 221 additions and 0 deletions

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PROGRAM=dht_sensor
EXTRA_COMPONENTS = extras/dht
include ../../common.mk

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/*
*
* This sample code is in the public domain.
*/
#include "espressif/esp_common.h"
#include "esp/uart.h"
#include "FreeRTOS.h"
#include "task.h"
#include "dht.h"
#include "esp8266.h"
/* An example using the ubiquitous DHT** humidity sensors
* to read and print a new temperature and humidity measurement
* from a sensor attached to GPIO pin 4.
*/
int const dht_gpio = 4;
void dhtMeasurementTask(void *pvParameters)
{
int8_t temperature = 0;
int8_t humidity = 0;
// DHT sensors that come mounted on a PCB generally have
// pull-up resistors on the data pin. It is recommended
// to provide an external pull-up resistor otherwise...
gpio_set_pullup(dht_gpio, false, false);
while(1) {
if (dht_fetch_data(dht_gpio, &humidity, &temperature)) {
printf("Humidity: %i%% Temp: %iC\n", humidity, temperature);
} else {
printf("Could not read data from sensor...");
}
// Three second delay...
vTaskDelay(3000 / portTICK_RATE_MS);
}
}
void user_init(void)
{
uart_set_baud(0, 115200);
xTaskCreate(dhtMeasurementTask, (signed char *)"dhtMeasurementTask", 256, NULL, 2, NULL);
}

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extras/dht/component.mk Normal file
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# Component makefile for extras/dht
INC_DIRS += $(ROOT)extras/dht
# args for passing into compile rule generation
extras/dht_INC_DIR = $(ROOT)extras/dht
extras/dht_SRC_DIR = $(ROOT)extras/dht
$(eval $(call component_compile_rules,extras/dht))

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

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extras/dht/dht.h Normal file
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/*
* Part of esp-open-rtos
* Copyright (C) 2016 Jonathan Hartsuiker (https://github.com/jsuiker)
* BSD Licensed as described in the file LICENSE
*
*/
#ifndef __DTH_H__
#define __DHT_H__
#include "FreeRTOS.h"
bool dht_wait_for_pin_state(uint8_t pin, uint8_t interval, uint8_t timeout, bool expected_pin_sate, uint8_t * counter);
bool dht_fetch_data(int8_t pin, int8_t * humidity, int8_t * temperature);
#endif