private DhtMeasurement CalculateResult()
{
byte[] bits = new byte[40];
int[] bytes = new int[5];
string bitStream = "";
DhtMeasurement measurement = new DhtMeasurement();
// we expect at least 1 raise and fall for the ack-bit and and 40 raise-fall combinations
if (_receivedSignal.Count >= 2 + 2 * 40)
{
Edge[] signals = _receivedSignal.Take(82).ToArray();
for (int bitNr = 0; bitNr < 40; bitNr++)
{
// substract the raise-time from the fall-time
int highInMicros = signals[2 + bitNr * 2 + 1].MicrosFromStart - signals[2 + bitNr * 2].MicrosFromStart;
bits[bitNr] = (highInMicros < OneBitHighTimeThresholdInMicros) ? (byte)0 : (byte)1;
bitStream += bits[bitNr].ToString() + "|";
int byteNr = bitNr / 8;
bytes[byteNr] = (bytes[byteNr] << 1) + bits[bitNr];
}
int checkSum = (bytes[0] + bytes[1] + bytes[2] + bytes[3]) & 0xff;
if (checkSum != bytes[4])
{
measurement.IsValid = false;
_errorMessage = string.Format("Checksum invalid. Expected: {0}, Calculated: {1}", bytes[4], checkSum);
return(measurement);
}
measurement.Humidity = (double)(256 * bytes[0] + bytes[1]) / 10;
measurement.Temperature = (double)((bytes[2] & 0x7f) * 256 + bytes[3]) / 10;
if ((bytes[2] & 0x80) > 0)
{
measurement.Temperature *= -1;
} // if first bit of MSB temperature then temp is negative
measurement.IsValid = true;
}
else
{
_errorMessage = String.Format("Only {0} signal changes registered, 82 expected.", _receivedSignal.Count);
}
return(measurement);
}
public DhtMeasurement GetMeasurement()
{
int maxRetries = 5;
int retries = 0;
DhtMeasurement measurement = new DhtMeasurement()
{
IsValid = false
};
while (retries < maxRetries)
{
InitializeDataMeasurement();
SendStartToSensor();
ReadSignalFromSensor();
measurement = CalculateResult();
if (measurement.IsValid)
{
break;
}
else if (_receivedSignal.Count == 81)
{
Edge edge = _receivedSignal.FirstOrDefault();
// missed just one edge, might be the first one.
Logging.LogMessage("Missed one edge from Dht22, first edge is {0} after micros: {1})", edge.NewValue.ToString(), edge.MicrosFromStart);
}
else if (retries > 0) // don't log first miss, happens more often
{
Logging.LogMessage("Invalid Dht22 sensor read, message: {0} (retryCount: {1})", ErrorMessage, retries);
}
// wait 2 seconds, so that sensor is able to recover...
Task.Delay(TimeSpan.FromSeconds(2)).Wait();
retries++;
}
_dhtPin.SetDriveMode(GpioPinDriveMode.Input);
return(measurement);
}