diff --git a/lib/sensor_dht22.c b/lib/sensor_dht22.c
new file mode 100644
index 0000000..8c97e31
--- /dev/null
+++ b/lib/sensor_dht22.c
@@ -0,0 +1,194 @@
+/* This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see .
+ *
+ */
+/** library to query measurements from Aosong DHT22 temperature and relative humidity sensor (code)
+ * @file sensor_dht22.c
+ * @author King Kévin
+ * @date 2017
+ * @note peripherals used: GPIO and timer @ref sensor_dht22_timer
+ * @note the DHT22 protocol is very similar but nit completely compatible with the DHT22 protocol: only 1 ms initial host pull low is required (vs. 18 ms), the data is encoded as int16_t (vs. uint8_t), and the signal has more jitter
+ */
+
+/* standard libraries */
+#include // standard integer types
+#include // maths utilities
+
+/* STM32 (including CM3) libraries */
+#include // Cortex M3 utilities
+#include // interrupt handler
+#include // real-time control clock library
+#include // general purpose input output library
+#include // timer utilities
+
+/* own libraries */
+#include "sensor_dht22.h" // PZEM electricity meter header and definitions
+#include "global.h" // common methods
+
+/** @defgroup sensor_dht22_timer timer peripheral used to measure signal timing for bit decoding
+ * @{
+ */
+#define SENSOR_DHT22_TIMER 4 /**< timer peripheral */
+#define SENSOR_DHT22_CHANNEL 3 /**< channel used as input capture */
+#define SENSOR_DHT22_JITTER 0.2 /**< signal timing jitter tolerated in timing */
+/** @} */
+
+volatile bool sensor_dht22_measurement_received = false;
+
+/** communication states */
+volatile enum sensor_dht22_state_t {
+ SENSOR_DHT22_OFF, // no request has started
+ SENSOR_DHT22_HOST_START, // host starts request (and waits >18ms)
+ SENSOR_DHT22_HOST_STARTED, // host started request and waits for slave answer
+ SENSOR_DHT22_SLAVE_START, // slave responds to request and puts signal low for 80 us and high for 80 us
+ SENSOR_DHT22_SLAVE_BIT, // slave is sending bit by putting signal low for 50 us and high (26-28 us = 0, 70 us = 1)
+ SENSOR_DHT22_MAX
+} sensor_dht22_state = SENSOR_DHT22_OFF; /**< current communication state */
+
+/** the bit number being sent (MSb first), up to 40 */
+volatile uint8_t sensor_dht22_bit = 0;
+
+/** the 40 bits (5 bytes) being sent by the device */
+volatile uint8_t sensor_dht22_bits[5] = {0};
+
+/** reset all states */
+static void sensor_dht22_reset(void)
+{
+ // reset states
+ sensor_dht22_state = SENSOR_DHT22_OFF;
+ sensor_dht22_bit = 0;
+ sensor_dht22_measurement_received = false;
+
+ gpio_set(TIM_CH_PORT(SENSOR_DHT22_TIMER,SENSOR_DHT22_CHANNEL), TIM_CH_PIN(SENSOR_DHT22_TIMER,SENSOR_DHT22_CHANNEL)); // idle is high (using pull-up resistor), pull-up before setting as output else the signal will be low for short
+ gpio_set_mode(TIM_CH_PORT(SENSOR_DHT22_TIMER,SENSOR_DHT22_CHANNEL), GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_OPENDRAIN, TIM_CH_PIN(SENSOR_DHT22_TIMER,SENSOR_DHT22_CHANNEL)); // setup GPIO pin as output (host starts communication before slave replies)
+
+ timer_ic_disable(TIM(SENSOR_DHT22_TIMER), TIM_IC(SENSOR_DHT22_CHANNEL)); // enable capture interrupt only when receiving data
+ timer_disable_counter(TIM(SENSOR_DHT22_TIMER)); // disable timer
+}
+
+void sensor_dht22_setup(void)
+{
+ // setup timer to measure signal timing for bit decoding (use timer channel as input capture)
+ rcc_periph_clock_enable(RCC_TIM_CH(SENSOR_DHT22_TIMER,SENSOR_DHT22_CHANNEL)); // enable clock for GPIO peripheral
+ rcc_periph_clock_enable(RCC_TIM(SENSOR_DHT22_TIMER)); // enable clock for timer peripheral
+ timer_reset(TIM(SENSOR_DHT22_TIMER)); // reset timer state
+ timer_set_mode(TIM(SENSOR_DHT22_TIMER), TIM_CR1_CKD_CK_INT, TIM_CR1_CMS_EDGE, TIM_CR1_DIR_UP); // set timer mode, use undivided timer clock,edge alignment (simple count), and count up
+ timer_set_prescaler(TIM(SENSOR_DHT22_TIMER), 2-1); // set the prescaler so this 16 bits timer allows to wait for 18 ms for the start signal ( 1/(72E6/2/(2**16))=1.820ms )
+ timer_ic_set_input(TIM(SENSOR_DHT22_TIMER), TIM_IC(SENSOR_DHT22_CHANNEL), TIM_IC_IN_TI(SENSOR_DHT22_CHANNEL)); // configure ICx to use TIn
+ timer_ic_set_filter(TIM(SENSOR_DHT22_TIMER), TIM_IC(SENSOR_DHT22_CHANNEL), TIM_IC_OFF); // use no filter input (precise timing needed)
+ timer_ic_set_polarity(TIM(SENSOR_DHT22_TIMER), TIM_IC(SENSOR_DHT22_CHANNEL), TIM_IC_FALLING); // capture on rising edge
+ timer_ic_set_prescaler(TIM(SENSOR_DHT22_TIMER), TIM_IC(SENSOR_DHT22_CHANNEL), TIM_IC_PSC_OFF); // don't use any prescaler since we want to capture every pulse
+
+ timer_clear_flag(TIM(SENSOR_DHT22_TIMER), TIM_SR_UIF); // clear flag
+ timer_update_on_overflow(TIM(SENSOR_DHT22_TIMER)); // only use counter overflow as UEV source (use overflow as start time or timeout)
+ timer_enable_irq(TIM(SENSOR_DHT22_TIMER), TIM_DIER_UIE); // enable update interrupt for timer
+
+ timer_clear_flag(TIM(SENSOR_DHT22_TIMER), TIM_SR_CCIF(SENSOR_DHT22_CHANNEL)); // clear input compare flag
+ timer_enable_irq(TIM(SENSOR_DHT22_TIMER), TIM_DIER_CCIE(SENSOR_DHT22_CHANNEL)); // enable capture interrupt
+
+ nvic_enable_irq(NVIC_TIM_IRQ(SENSOR_DHT22_TIMER)); // catch interrupt in service routine
+
+ sensor_dht22_reset(); // reset state
+}
+
+bool sensor_dht22_measurement_request(void)
+{
+ if (sensor_dht22_state!=SENSOR_DHT22_OFF) { // not the right state to start (wait up until timeout to reset state)
+ return false;
+ }
+ if (gpio_get(TIM_CH_PORT(SENSOR_DHT22_TIMER,SENSOR_DHT22_CHANNEL), TIM_CH_PIN(SENSOR_DHT22_TIMER,SENSOR_DHT22_CHANNEL))==0) { // signal should be high per default
+ return false;
+ }
+ if (TIM_CR1(TIM(SENSOR_DHT22_TIMER))&(TIM_CR1_CEN)) { // timer should be off
+ return false;
+ }
+ sensor_dht22_reset(); // reset states
+
+ // send start signal (pull low for > 1 ms)
+ gpio_clear(TIM_CH_PORT(SENSOR_DHT22_TIMER,SENSOR_DHT22_CHANNEL), TIM_CH_PIN(SENSOR_DHT22_TIMER,SENSOR_DHT22_CHANNEL)); // set signal to low
+ timer_set_counter(TIM(SENSOR_DHT22_TIMER), 0); // reset timer counter
+ timer_enable_counter(TIM(SENSOR_DHT22_TIMER)); // enable timer to wait for 1.8 ms until overflow
+ sensor_dht22_state = SENSOR_DHT22_HOST_START; // remember we started sending signal
+
+ return true;
+}
+
+struct sensor_dht22_measurement_t sensor_dht22_measurement_decode(void)
+{
+ struct sensor_dht22_measurement_t measurement = { NAN, NAN }; // measurement to return
+ if (sensor_dht22_bit<40) { // not enough bits received
+ return measurement;
+ }
+ if ((uint8_t)(sensor_dht22_bits[0]+sensor_dht22_bits[1]+sensor_dht22_bits[2]+sensor_dht22_bits[3])!=sensor_dht22_bits[4]) { // error in checksum (not really parity bit, as mentioned in the datasheet)
+ return measurement;
+ }
+ // calculate measured values (stored as uint16_t deci-value)
+ measurement.humidity = (int16_t)((sensor_dht22_bits[0]<<8)+sensor_dht22_bits[1])/10.0;
+ measurement.temperature = (int16_t)((sensor_dht22_bits[2]<<8)+sensor_dht22_bits[3])/10.0;
+
+ return measurement;
+}
+
+/** interrupt service routine called for timer */
+void TIM_ISR(SENSOR_DHT22_TIMER)(void)
+{
+ if (timer_get_flag(TIM(SENSOR_DHT22_TIMER), TIM_SR_UIF)) { // overflow update event happened
+ timer_clear_flag(TIM(SENSOR_DHT22_TIMER), TIM_SR_UIF); // clear flag
+ if (sensor_dht22_state==SENSOR_DHT22_HOST_START) { // start signal sent
+ gpio_set_mode(TIM_CH_PORT(SENSOR_DHT22_TIMER,SENSOR_DHT22_CHANNEL), GPIO_MODE_INPUT, GPIO_CNF_INPUT_FLOAT, TIM_CH_PIN(SENSOR_DHT22_TIMER,SENSOR_DHT22_CHANNEL)); // switch pin to input (the external pull up with also set the signal high)
+ sensor_dht22_state = SENSOR_DHT22_HOST_STARTED; // switch to next state
+ timer_ic_enable(TIM(SENSOR_DHT22_TIMER), TIM_IC(SENSOR_DHT22_CHANNEL)); // enable capture interrupt only when receiving data
+ } else { // timeout occurred
+ sensor_dht22_reset(); // reset states
+ }
+ } else if (timer_get_flag(TIM(SENSOR_DHT22_TIMER), TIM_SR_CCIF(SENSOR_DHT22_CHANNEL))) { // edge detected on input capture
+ uint16_t time = TIM_CCR(SENSOR_DHT22_TIMER,SENSOR_DHT22_CHANNEL); // save captured bit timing (this clear also the flag)
+ timer_set_counter(TIM(SENSOR_DHT22_TIMER), 0); // reset timer counter
+ time = (time*1E6)/(rcc_ahb_frequency/(TIM_PSC(TIM(SENSOR_DHT22_TIMER))+1)); // calculate time in us
+ switch (sensor_dht22_state) {
+ case (SENSOR_DHT22_HOST_STARTED): // the host query data and the slave is responding
+ sensor_dht22_state = SENSOR_DHT22_SLAVE_START; // set new state
+ break;
+ case (SENSOR_DHT22_SLAVE_START): // the slave sent the start signal
+ if (time >= ((80+80)*(1-SENSOR_DHT22_JITTER)) && time <= ((80+80)*(1+SENSOR_DHT22_JITTER))) { // response time should be 80 us low and 80 us high
+ sensor_dht22_state = SENSOR_DHT22_SLAVE_BIT; // set new state
+ } else {
+ goto error;
+ }
+ break;
+ case (SENSOR_DHT22_SLAVE_BIT): // the slave sent a bit
+ if (sensor_dht22_bit>=40) { // no bits should be received after 40 bits
+ goto error;
+ }
+ if (time >= ((50+26)*(1-SENSOR_DHT22_JITTER)) && time <= ((50+28)*(1+SENSOR_DHT22_JITTER))) { // bit 0 time should be 50 us low and 26-28 us high
+ sensor_dht22_bits[sensor_dht22_bit/8] &= ~(1<<(7-(sensor_dht22_bit%8))); // clear bit
+ } else if (time >= ((50+70)*(1-SENSOR_DHT22_JITTER)) && time <= ((50+70)*(1+SENSOR_DHT22_JITTER))) { // bit 1 time should be 50 us low and 70 us high
+ sensor_dht22_bits[sensor_dht22_bit/8] |= (1<<(7-(sensor_dht22_bit%8))); // set bit
+ } else {
+ goto error;
+ }
+ sensor_dht22_bit++;
+ if (sensor_dht22_bit>=40) { // all bits received
+ sensor_dht22_reset(); // reset states
+ sensor_dht22_bit = 40; // signal decoder all bits have been received
+ sensor_dht22_measurement_received = true; // signal user all bits have been received
+ }
+ break;
+ default: // unexpected state
+error:
+ sensor_dht22_reset(); // reset states
+ }
+ } else { // no other interrupt should occur
+ while (true); // unhandled exception: wait for the watchdog to bite
+ }
+}
diff --git a/lib/sensor_dht22.h b/lib/sensor_dht22.h
new file mode 100644
index 0000000..ba2b4d9
--- /dev/null
+++ b/lib/sensor_dht22.h
@@ -0,0 +1,41 @@
+/* This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see .
+ *
+ */
+/** library to query measurements from Aosong DHT22 (aka. AM2302) temperature and relative humidity sensor (API)
+ * @file sensor_dht22.h
+ * @author King Kévin
+ * @date 2017
+ * @note peripherals used: timer channel @ref sensor_dht22_timer (add external pull-up resistor)
+ */
+#pragma once
+
+/** a measurement response has been received */
+extern volatile bool sensor_dht22_measurement_received;
+
+/** measurement returned by sensor */
+struct sensor_dht22_measurement_t {
+ float humidity; /**< relative humidity in %RH (0-100) */
+ float temperature; /**< temperature in °C (-40-80) */
+};
+
+/** setup peripherals to communicate with sensor */
+void sensor_dht22_setup(void);
+/** request measurement from sensor
+ * @return request started successfully
+ */
+bool sensor_dht22_measurement_request(void);
+/** decode received measurement
+ * @return decoded measurement (0xff,0xff if invalid)
+ */
+struct sensor_dht22_measurement_t sensor_dht22_measurement_decode(void);