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Fix support for Si7021 and clarify timing comments

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Fixed conversion of the Si7021 data and fully tested over large temperature / humidity range.
Also tested the AM2301 sensor (often used as alternative to Si7021)
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David Dix 2019-11-29 23:47:30 +00:00 committed by GitHub
parent 6d755943e0
commit 1ce1fa0e37
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GPG key ID: 4AEE18F83AFDEB23
1 changed files with 12 additions and 8 deletions
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20
extras/dht/dht.c
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@ -35,11 +35,18 @@
* *
* Initializing communications with the DHT requires four 'phases' as follows: * Initializing communications with the DHT requires four 'phases' as follows:
* *
* Phase A - MCU pulls signal low for at least 18000 us * Phase A - MCU pulls signal low for a period (see below)
* Phase B - MCU allows signal to float back up and waits 20-40us for DHT to pull it low * Phase B - MCU allows signal to float back up and waits 20-200us for DHT to pull it low
* Phase C - DHT pulls signal low for ~80us * Phase C - DHT pulls signal low for ~80us
* Phase D - DHT lets signal float back up for ~80us * Phase D - DHT lets signal float back up for ~80us
* *
* The length of Phase A is dependent on the sensor type:
* DHT_TYPE_DHT11 : at least 18000 us
* DHT_TYPE_DHT22 : 800 us to 20000 us, typically 1100 us
* DHT_TYPE_SI7021 : 300 us to 500 us
* For a DHT21 use DHT_TYPE_DHT22
* For an AM2301/AM2302 use DHT_TYPE_SI7021
*
* After this, the DHT transmits its first bit by holding the signal low for 50us * 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. * 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'. * duration_data_high is shorter than 50us for a logic '0' and longer than 50us for logic '1'.
@ -91,8 +98,8 @@ static inline bool dht_fetch_data(dht_sensor_type_t sensor_type, uint8_t pin, bo
sdk_os_delay_us(sensor_type == DHT_TYPE_SI7021 ? 500 : 20000); sdk_os_delay_us(sensor_type == DHT_TYPE_SI7021 ? 500 : 20000);
gpio_write(pin, 1); gpio_write(pin, 1);
// Step through Phase 'B', 40us // Step through Phase 'B', 200us
if (!dht_await_pin_state(pin, 40, false, NULL)) { if (!dht_await_pin_state(pin, 200, false, NULL)) {
debug("Initialization error, problem in phase 'B'\n"); debug("Initialization error, problem in phase 'B'\n");
return false; return false;
} }
@ -131,7 +138,7 @@ static inline int16_t dht_convert_data(dht_sensor_type_t sensor_type, uint8_t ms
{ {
int16_t data; int16_t data;
if (sensor_type == DHT_TYPE_DHT22) { if (sensor_type == DHT_TYPE_DHT22 || sensor_type == DHT_TYPE_SI7021) {
data = msb & 0x7F; data = msb & 0x7F;
data <<= 8; data <<= 8;
data |= lsb; data |= lsb;
@ -139,9 +146,6 @@ static inline int16_t dht_convert_data(dht_sensor_type_t sensor_type, uint8_t ms
data = 0 - data; // convert it to negative data = 0 - data; // convert it to negative
} }
} }
else if (sensor_type == DHT_TYPE_SI7021) {
data = msb * 256 + (lsb & ~0x3);
}
else { else {
data = msb * 10; data = msb * 10;
} }