Initial Release

gpio/dht_sensor/dht.c

@@ -0,0 +1,83 @@
+/**
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ **/
+
+#include <stdio.h>
+#include <math.h>
+#include "pico/stdlib.h"
+#include "hardware/gpio.h"
+
+const uint LED_PIN = PICO_DEFAULT_LED_PIN;
+const uint DHT_PIN = 15;
+const uint MAX_TIMINGS = 85;
+
+typedef struct {
+    float humidity;
+    float temp_celsius;
+} dht_reading;
+
+void read_from_dht(dht_reading *result);
+
+int main() {
+    stdio_init_all();
+    gpio_init(LED_PIN);
+    gpio_init(DHT_PIN);
+    gpio_set_dir(LED_PIN, GPIO_OUT);
+    while (1) {
+        dht_reading reading;
+        read_from_dht(&reading);
+        float fahrenheit = (reading.temp_celsius * 9 / 5) + 32;
+        printf("Humidity = %.1f%%, Temperature = %.1fC (%.1fF)\n",
+               reading.humidity, reading.temp_celsius, fahrenheit);
+
+        sleep_ms(2000);
+    }
+}
+
+void read_from_dht(dht_reading *result) {
+    int data[5] = {0, 0, 0, 0, 0};
+    uint last = 1;
+    uint j = 0;
+
+    gpio_set_dir(DHT_PIN, GPIO_OUT);
+    gpio_put(DHT_PIN, 0);
+    sleep_ms(20);
+    gpio_set_dir(DHT_PIN, GPIO_IN);
+
+    gpio_put(LED_PIN, 1);
+    for (uint i = 0; i < MAX_TIMINGS; i++) {
+        uint count = 0;
+        while (gpio_get(DHT_PIN) == last) {
+            count++;
+            sleep_us(1);
+            if (count == 255) break;
+        }
+        last = gpio_get(DHT_PIN);
+        if (count == 255) break;
+
+        if ((i >= 4) && (i % 2 == 0)) {
+            data[j / 8] <<= 1;
+            if (count > 16) data[j / 8] |= 1;
+            j++;
+        }
+    }
+    gpio_put(LED_PIN, 0);
+
+    if ((j >= 40) && (data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF))) {
+        result->humidity = (float) ((data[0] << 8) + data[1]) / 10;
+        if (result->humidity > 100) {
+            result->humidity = data[0];
+        }
+        result->temp_celsius = (float) (((data[2] & 0x7F) << 8) + data[3]) / 10;
+        if (result->temp_celsius > 125) {
+            result->temp_celsius = data[2];
+        }
+        if (data[2] & 0x80) {
+            result->temp_celsius = -result->temp_celsius;
+        }
+    } else {
+        printf("Bad data\n");
+    }
+}