A minimal library for the DHT11.
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Diff: Dht22.cpp
- Revision:
- 2:1460b7a50ec0
- Parent:
- 1:5da6f6de3e42
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/Dht22.cpp Fri Nov 10 20:28:29 2017 +0000 @@ -0,0 +1,104 @@ +#include "Dht22.h" + +Dht22::Dht22(PinName const &p) : _pin(p) { + // Set creation time so we can make + // sure we pause at least 1 second for + // startup. + _timer.start(); + + _temperature = 0; + _humidity = 0; +} + +int Dht22::read() +{ + // BUFFER TO RECEIVE + uint8_t bits[5]; + uint8_t cnt = 7; + uint8_t idx = 0; + + // EMPTY BUFFER + for (int i=0; i< 5; i++) bits[i] = 0; + + // Verify sensor settled after boot + while(_timer.read_ms() < 1500) {} + _timer.stop(); + + // Notify it we are ready to read + _pin.output(); + _pin = 0; + wait_ms(18); + _pin = 1; + wait_us(40); + _pin.input(); + + // ACKNOWLEDGE or TIMEOUT + unsigned int loopCnt = 10000; + while(_pin == 0) + if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT; + + loopCnt = 10000; + while(_pin == 1) + if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT; + + // READ OUTPUT - 40 BITS => 5 BYTES or TIMEOUT + for (int i=0; i<40; i++) + { + loopCnt = 10000; + while(_pin == 0) + if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT; + + //unsigned long t = micros(); + Timer t; + t. start(); + + loopCnt = 10000; + while(_pin == 1) + if (loopCnt-- == 0) return DHTLIB_ERROR_TIMEOUT; + + if (t.read_us() > 40) bits[idx] |= (1 << cnt); + if (cnt == 0) // next byte? + { + cnt = 7; // restart at MSB + idx++; // next byte! + } + else cnt--; + } + +// // WRITE TO RIGHT VARS - DHT22 +// // as bits[1] and bits[3] are allways zero they are omitted in formulas. +// _humidity = bits[0]; +// _temperature = bits[2]; +// +// uint8_t sum = bits[0] + bits[2]; +// +// if (bits[4] != sum) return DHTLIB_ERROR_CHECKSUM; + + + uint8_t dht22_check_sum; + dht22_check_sum = bits[0] + bits[1] + bits[2] + bits[3]; + //printf("dht22 check sum: %d",dht22_check_sum); + dht22_check_sum= dht22_check_sum%256; + //printf("dht22 check sum: %d",dht22_check_sum); + + if (dht22_check_sum == bits[4]) { + _humidity = bits[0]*256 + bits[1]; + + _temperature = bits[2]*256 + bits[3]; + //printf("all good \n"); + return DHTLIB_OK; + } + return DHTLIB_ERROR_CHECKSUM; +} + +float Dht22::getFahrenheit() { + return((_temperature * 1.8) + 32); +} + +int Dht22::getCelsius() { + return(_temperature); +} + +int Dht22::getHumidity() { + return(_humidity); +}