diff --git a/DHT.cpp b/DHT.cpp index f349934..83d2268 100644 --- a/DHT.cpp +++ b/DHT.cpp @@ -140,62 +140,63 @@ boolean DHT::read(void) { // Turn off interrupts temporarily because the next sections are timing critical // and we don't want any interruptions. - noInterrupts(); + { + InterruptLock lock; - // End the start signal by setting data line high for 40 microseconds. - digitalWrite(_pin, HIGH); - delayMicroseconds(40); + // End the start signal by setting data line high for 40 microseconds. + digitalWrite(_pin, HIGH); + delayMicroseconds(40); - // Now start reading the data line to get the value from the DHT sensor. - pinMode(_pin, INPUT); - delayMicroseconds(10); // Delay a bit to let sensor pull data line low. + // Now start reading the data line to get the value from the DHT sensor. + pinMode(_pin, INPUT); + delayMicroseconds(10); // Delay a bit to let sensor pull data line low. - // First expect a low signal for ~80 microseconds followed by a high signal - // for ~80 microseconds again. - if (expectPulse(LOW) == 0) { - DEBUG_PRINTLN(F("Timeout waiting for start signal low pulse.")); - _lastresult = false; - return _lastresult; - } - if (expectPulse(HIGH) == 0) { - DEBUG_PRINTLN(F("Timeout waiting for start signal high pulse.")); - _lastresult = false; - return _lastresult; - } - - // Now read the 40 bits sent by the sensor. Each bit is sent as a 50 - // microsecond low pulse followed by a variable length high pulse. If the - // high pulse is ~28 microseconds then it's a 0 and if it's ~70 microseconds - // then it's a 1. We measure the cycle count of the initial 50us low pulse - // and use that to compare to the cycle count of the high pulse to determine - // if the bit is a 0 (high state cycle count < low state cycle count), or a - // 1 (high state cycle count > low state cycle count). - for (int i=0; i<40; ++i) { - uint32_t lowCycles = expectPulse(LOW); - if (lowCycles == 0) { - DEBUG_PRINTLN(F("Timeout waiting for bit low pulse.")); + // First expect a low signal for ~80 microseconds followed by a high signal + // for ~80 microseconds again. + if (expectPulse(LOW) == 0) { + DEBUG_PRINTLN(F("Timeout waiting for start signal low pulse.")); _lastresult = false; return _lastresult; } - uint32_t highCycles = expectPulse(HIGH); - if (highCycles == 0) { - DEBUG_PRINTLN(F("Timeout waiting for bit high pulse.")); + if (expectPulse(HIGH) == 0) { + DEBUG_PRINTLN(F("Timeout waiting for start signal high pulse.")); _lastresult = false; return _lastresult; } - data[i/8] <<= 1; - // Now compare the low and high cycle times to see if the bit is a 0 or 1. - if (highCycles > lowCycles) { - // High cycles are greater than 50us low cycle count, must be a 1. - data[i/8] |= 1; - } - // Else high cycles are less than (or equal to, a weird case) the 50us low - // cycle count so this must be a zero. Nothing needs to be changed in the - // stored data. - } - // Re-enable interrupts, timing critical code is complete. - interrupts(); + // Now read the 40 bits sent by the sensor. Each bit is sent as a 50 + // microsecond low pulse followed by a variable length high pulse. If the + // high pulse is ~28 microseconds then it's a 0 and if it's ~70 microseconds + // then it's a 1. We measure the cycle count of the initial 50us low pulse + // and use that to compare to the cycle count of the high pulse to determine + // if the bit is a 0 (high state cycle count < low state cycle count), or a + // 1 (high state cycle count > low state cycle count). + for (int i=0; i<40; ++i) { + uint32_t lowCycles = expectPulse(LOW); + if (lowCycles == 0) { + DEBUG_PRINTLN(F("Timeout waiting for bit low pulse.")); + _lastresult = false; + return _lastresult; + } + uint32_t highCycles = expectPulse(HIGH); + if (highCycles == 0) { + DEBUG_PRINTLN(F("Timeout waiting for bit high pulse.")); + _lastresult = false; + return _lastresult; + } + data[i/8] <<= 1; + // Now compare the low and high cycle times to see if the bit is a 0 or 1. + if (highCycles > lowCycles) { + // High cycles are greater than 50us low cycle count, must be a 1. + data[i/8] |= 1; + } + // Else high cycles are less than (or equal to, a weird case) the 50us low + // cycle count so this must be a zero. Nothing needs to be changed in the + // stored data. + } + // Timing critical code is now complete. + + } DEBUG_PRINTLN(F("Received:")); DEBUG_PRINT(data[0], HEX); DEBUG_PRINT(F(", ")); diff --git a/DHT.h b/DHT.h index 41e66fe..fbcacd6 100644 --- a/DHT.h +++ b/DHT.h @@ -57,4 +57,15 @@ class DHT { }; +class InterruptLock { + public: + InterruptLock() { + noInterrupts(); + } + ~InterruptLock() { + interrupts(); + } + +}; + #endif