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DHT sensors protocol revision and refactoring #7468

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DHT sensors protocol revision and refactoring #7468

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68 changes: 56 additions & 12 deletions tasmota/xsns_06_dht.ino
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Original file line number Diff line number Diff line change
Expand Up @@ -72,28 +72,70 @@ bool DhtRead(uint8_t sensor)

dht_data[0] = dht_data[1] = dht_data[2] = dht_data[3] = dht_data[4] = 0;

// digitalWrite(Dht[sensor].pin, HIGH);
// delay(250);

if (Dht[sensor].lastresult > DHT_MAX_RETRY) {
Dht[sensor].lastresult = 0;
digitalWrite(Dht[sensor].pin, HIGH); // Retry read prep
delay(250);
}

// Activate sensor using its protocol
noInterrupts();
pinMode(Dht[sensor].pin, OUTPUT);
digitalWrite(Dht[sensor].pin, LOW);

if (GPIO_SI7021 == Dht[sensor].type) {
delayMicroseconds(500);
} else {
delay(20);
switch (Dht[sensor].type) {
case GPIO_SI7021: // Start protocol for iTead SI7021
/*
Protocol:
Reverse-engineered on https://github.com/arendst/Tasmota/issues/735#issuecomment-348718383:
1. MCU PULLS LOW data bus for at 500us to activate sensor
2. MCU PULLS UP data bus for ~40us to ask sensor for response
3. SENSOR starts sending data (LOW 40us then HIGH ~25us for "0" or ~75us for "1")
4. SENSOR sends "1" start bit as a response
5. SENSOR sends 16 bits (2 bytes) of a humidity with one decimal (i.e. 35.6% is sent as 356)
6. SENSOR sends 16 bits (2 bytes) of a temperature with one decimal (i.e. 23.4C is sent as 234)
7. SENSOR sends 8 bits (1 byte) checksum of 4 data bytes
*/
digitalWrite(Dht[sensor].pin, LOW);
delayMicroseconds(500);
digitalWrite(Dht[sensor].pin, HIGH);
delayMicroseconds(40);
break;

case GPIO_DHT22: // Start protocol for DHT21, DHT22, AM2301, AM2302, AM2321
/*
Protocol:
1. MCU PULLS LOW data bus for 1 to 10ms to activate sensor
2. MCU PULLS UP data bus for 20-40us to ask sensor for response
3. SENSOR PULLS LOW data bus for 80us as a response
4. SENSOR PULLS UP data bus for 80us for data sending preparation
5. SENSOR starts sending data (LOW 50us then HIGH 26-28us for "0" or 70us for "1")
*/
digitalWrite(Dht[sensor].pin, LOW);
delayMicroseconds(1100); // data sheet says "at least 1ms to 10ms"
digitalWrite(Dht[sensor].pin, HIGH);
delayMicroseconds(30); // data sheet says "20 to 40us"
break;

case GPIO_DHT11: // Start protocol for DHT11
/*
Protocol:
1. MCU PULLS LOW data bus for at least 18ms to activate sensor
2. MCU PULLS UP data bus for 20-40us to ask sensor for response
3. SENSOR PULLS LOW data bus for 80us as a response
4. SENSOR PULLS UP data bus for 80us for data sending preparation
5. SENSOR starts sending data (LOW 50us then HIGH 26-28us for "0" or 70 us for "1")
*/
default:
digitalWrite(Dht[sensor].pin, LOW);
delay(20); // data sheet says at least 18ms, 20ms just to be safe
digitalWrite(Dht[sensor].pin, HIGH);
delayMicroseconds(30); // data sheet says "20 to 40us"
break;
}

noInterrupts();
digitalWrite(Dht[sensor].pin, HIGH);
delayMicroseconds(40);
// Listen to the sensor response
pinMode(Dht[sensor].pin, INPUT_PULLUP);
delayMicroseconds(10);

if (-1 == DhtExpectPulse(sensor, LOW)) {
AddLog_P(LOG_LEVEL_DEBUG, PSTR(D_LOG_DHT D_TIMEOUT_WAITING_FOR " " D_START_SIGNAL_LOW " " D_PULSE));
error = 1;
Expand All @@ -111,6 +153,7 @@ bool DhtRead(uint8_t sensor)
interrupts();
if (error) { return false; }

// Decode response
for (uint32_t i = 0; i < 40; ++i) {
int32_t lowCycles = cycles[2*i];
int32_t highCycles = cycles[2*i+1];
Expand All @@ -124,6 +167,7 @@ bool DhtRead(uint8_t sensor)
}
}

// Check response
uint8_t checksum = (dht_data[0] + dht_data[1] + dht_data[2] + dht_data[3]) & 0xFF;
if (dht_data[4] != checksum) {
char hex_char[15];
Expand Down