Merge pull request #159 from sheinz/fix/dht

DHT11/DHT22 sensor library fixed.

examples/dht_sensor/dht_sensor.c

@@ -2,6 +2,8 @@
  *
  * This sample code is in the public domain.
  */
+#include <stdio.h>
+#include <stdlib.h>
 #include "espressif/esp_common.h"
 #include "esp/uart.h"
 #include "FreeRTOS.h"
@@ -13,12 +15,12 @@
  * to read and print a new temperature and humidity measurement
  * from a sensor attached to GPIO pin 4.
  */
-int const dht_gpio = 4;
+uint8_t const dht_gpio = 4;
 
 void dhtMeasurementTask(void *pvParameters)
 {
-  int8_t temperature = 0;
+    int16_t temperature = 0;
-  int8_t humidity = 0;
+    int16_t humidity = 0;
 
     // DHT sensors that come mounted on a PCB generally have
     // pull-up resistors on the data pin.  It is recommended
@@ -26,11 +28,12 @@ void dhtMeasurementTask(void *pvParameters)
     gpio_set_pullup(dht_gpio, false, false);
 
     while(1) {
-
+        if (dht_read_data(dht_gpio, &humidity, &temperature)) {
-    if (dht_fetch_data(dht_gpio, &humidity, &temperature)) {
+            printf("Humidity: %d%% Temp: %dC\n", 
-      printf("Humidity: %i%% Temp: %iC\n", humidity, temperature);
+                    humidity / 10, 
+                    temperature / 10);
         } else {
-      printf("Could not read data from sensor...");
+            printf("Could not read data from sensor\n");
         }
 
         // Three second delay...

extras/dht/dht.c

@@ -6,17 +6,20 @@
  */
 
 #include "dht.h"
+#include "FreeRTOS.h"
 #include "string.h"
 #include "task.h"
 #include "esp/gpio.h"
 
 #include <espressif/esp_misc.h> // sdk_os_delay_us
 
-#ifndef DEBUG_DHT
+// DHT timer precision in microseconds
-#define DEBUG_DHT 0
+#define DHT_TIMER_INTERVAL   2
-#endif
+#define DHT_DATA_BITS  40
 
-#if DEBUG_DHT
+// #define DEBUG_DHT
+
+#ifdef DEBUG_DHT
 #define debug(fmt, ...) printf("%s" fmt "\n", "dht: ", ## __VA_ARGS__);
 #else
 #define debug(fmt, ...) /* (do nothing) */
@@ -42,7 +45,7 @@
  *  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
+ *  There are a total of 40 data bits transmitted 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:
  *
@@ -50,95 +53,144 @@
  *
 */
 
-/*  
+
- *  @pin                    the selected GPIO pin
+/**
- *  @interval               how frequently the pin state is checked in microseconds
+ * Wait specified time for pin to go to a specified state.
- *  @timeout                maximum length of time to wait for the expected pin state
+ * If timeout is reached and pin doesn't go to a requested state
- *  @expected_pin_state     high (true) or low (false) pin state
+ * false is returned.
- *  @counter                pointer to external uint8_t for tallying the duration waited for the pin state
+ * The elapsed time is returned in pointer 'duration' if it is not NULL.
  */
-
+static bool dht_await_pin_state(uint8_t pin, uint32_t timeout,
-bool dht_await_pin_state(uint8_t pin, uint8_t interval, uint8_t timeout, bool expected_pin_state, uint8_t * counter) {
+        bool expected_pin_state, uint32_t *duration)
-
+{
-    for (*counter = 0; *counter < timeout; *counter+=interval) {
+    for (uint32_t i = 0; i < timeout; i += DHT_TIMER_INTERVAL) {
-        if (gpio_read(pin) == expected_pin_state) return true;
+        // need to wait at least a single interval to prevent reading a jitter
-        sdk_os_delay_us(interval);
+        sdk_os_delay_us(DHT_TIMER_INTERVAL);
+        if (gpio_read(pin) == expected_pin_state) {
+            if (duration) {
+                *duration = i;
+            }
+            return true;
+        }
     }
 
     return false;
 }
 
-/*  
+/**
- *  
+ * Request data from DHT and read raw bit stream.
- *  
+ * The function call should be protected from task switching.
- *  @pin                    the selected GPIO pin
+ * Return false if error occurred.
- *  @humidity               pointer to external int8_t to store resulting humidity value
- *  @temperature            pointer to external int8_t to store resulting temperature value
  */
-
+static inline bool dht_fetch_data(uint8_t pin, bool bits[DHT_DATA_BITS])
-bool dht_fetch_data(int8_t pin, int8_t * humidity, int8_t * temperature) {
+{
-    int8_t data[40] = {0};
+    uint32_t low_duration;
-    int8_t result[5] = {0};
+    uint32_t high_duration;
-    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
+    // Step through Phase 'B', 40us
-    if (dht_await_pin_state(pin, 2, 40, false, &init_phase_duration)) {
+    if (!dht_await_pin_state(pin, 40, false, NULL)) {
-        // Step through Phase 'C ' at 2us intervals, 88us max
+        debug("Initialization error, problem in phase 'B'\n");
-        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;
     }
 
+    // Step through Phase 'C', 88us
+    if (!dht_await_pin_state(pin, 88, true, NULL)) {
+        debug("Initialization error, problem in phase 'C'\n");
+        return false;
+    }
+
+    // Step through Phase 'D', 88us
+    if (!dht_await_pin_state(pin, 88, false, NULL)) {
+        debug("Initialization error, problem in phase 'D'\n");
+        return false;
+    }
+
+    // Read in each of the 40 bits of data...
+    for (int i = 0; i < DHT_DATA_BITS; i++) {
+        if (!dht_await_pin_state(pin, 65, true, &low_duration)) {
+            debug("LOW bit timeout\n");
+            return false;
+        }
+        if (!dht_await_pin_state(pin, 75, false, &high_duration)){
+            debug("HIGHT bit timeout\n");
+            return false;
+        }
+        bits[i] = high_duration > low_duration;
+    }
+    return true;
+}
+
+/**
+ * Pack two data bytes into single value and take into account sign bit.
+ */
+static inline int16_t dht_convert_data(uint8_t msb, uint8_t lsb)
+{
+    int16_t data;
+
+#if DHT_TYPE == DHT22
+    data = msb & 0x7F;
+    data <<= 8;
+    data |= lsb;
+    if (msb & BIT(7)) {
+        data = 0 - data;       // convert it to negative
+    }
+#elif DHT_TYPE == DHT11
+    data = msb * 10;
+#else
+#error "Unsupported DHT type"
+#endif
+
+    return data;
+}
+
+bool dht_read_data(uint8_t pin, int16_t *humidity, int16_t *temperature)
+{
+    bool bits[DHT_DATA_BITS];
+    uint8_t data[DHT_DATA_BITS/8] = {0};
+    bool result;
+
+    gpio_enable(pin, GPIO_OUT_OPEN_DRAIN);
+
+    taskENTER_CRITICAL();
+    result = dht_fetch_data(pin, bits);
+    taskEXIT_CRITICAL();
+
+    if (!result) {
+        return false;
+    }
+
+    for (uint8_t i = 0; i < DHT_DATA_BITS; i++) {
+        // Read each bit into 'result' byte array...
+        data[i/8] <<= 1;
+        data[i/8] |= bits[i];
+    }
+
+    if (data[4] != ((data[0] + data[1] + data[2] + data[3]) & 0xFF)) {
+        debug("Checksum failed, invalid data received from sensor\n");
+        return false;
+    }
+
+    *humidity = dht_convert_data(data[0], data[1]);
+    *temperature = dht_convert_data(data[2], data[3]);
+
+    debug("Sensor data: humidity=%d, temp=%d\n", *humidity, *temperature);
+
+    return true;
+}
+
+bool dht_read_float_data(uint8_t pin, float *humidity, float *temperature)
+{
+    int16_t i_humidity, i_temp;
+
+    if (dht_read_data(pin, &i_humidity, &i_temp)) {
+        *humidity = (float)i_humidity / 10;
+        *temperature = (float)i_temp / 10;
+        return true;
+    }
+    return false;
+}

extras/dht/dht.h

@@ -5,13 +5,34 @@
  *
  */
 
-#ifndef __DTH_H__
+#ifndef __DHT_H__
 #define __DHT_H__
 
-#include "FreeRTOS.h"
+#include <stdint.h>
+#include <stdbool.h>
 
-bool dht_wait_for_pin_state(uint8_t pin, uint8_t interval, uint8_t timeout, bool expected_pin_sate, uint8_t * counter);
+#define DHT11       11
-bool dht_fetch_data(int8_t pin, int8_t * humidity, int8_t * temperature);
+#define DHT22       22
 
-#endif
+// Type of sensor to use
+#define DHT_TYPE    DHT22
 
+/**
+ * Read data from sensor on specified pin.
+ *
+ * Humidity and temperature is returned as integers.
+ * For example: humidity=625 is 62.5 %
+ *              temperature=24.4 is 24.4 degrees Celsius
+ *
+ */
+bool dht_read_data(uint8_t pin, int16_t *humidity, int16_t *temperature);
+
+
+/**
+ * Float version of dht_read_data.
+ *
+ * Return values as floating point values.
+ */
+bool dht_read_float_data(uint8_t pin, float *humidity, float *temperature);
+
+#endif  // __DHT_H__