public DhtData GetData()
{
// pull pin down for 18ms
pin.Write(false);
Timer.Sleep(18m);
// pull pin up for 40µs
pin.Write(true);
Timer.Sleep(40m / 1000m);
pin.Wait(true, 40m / 1000m);
// Wait for pin to be down (at most 80µs)
pin.Wait(false, 80m / 1000m);
// Wait for pin to be up (at most 80µs)
pin.Wait(true, 80m / 1000m);
var data = new byte[] { 0, 0, 0, 0, 0 };
for (var i = 0; i < 5; i++)
{
for (var j = 0; j < 8; j++)
{
pin.Wait(false, 50m / 1000m);
var start = DateTime.UtcNow;
pin.Wait(true, 100m / 1000m);
// bit "0" has 26-28us high-voltage length, bit "1" has 70us high-voltage length
var value = (DateTime.UtcNow - start).TotalMilliseconds > 40.0 / 1000 ? 1 : 0;
data[i] = (byte)(data[i] << 1 + value);
}
}
Console.WriteLine(
"{0:X2} {1:X2} {2:X2} {3:X2} {4:X2}",
data[0],
data[1],
data[2],
data[3],
data[4]);
var checkSum = data[0] + data[1] + data[2] + data[3];
if ((checkSum & 0xff) != data[4])
{
throw new InvalidOperationException("Checksum is not valid");
}
pin.Write(true);
return(new DhtData
{
Humidity = (data[0] << 8 + data[1]) / 10.0m,
Temperature = ((data[2] & 0x80) == 0 ? 1 : -1) * ((data[2] & 0x7F) << 8 + data[3]) / 10.0m
});
}
private DhtData TryGetData()
{
// Prepare buffer
var data = new byte[5];
for (var i = 0; i < 5; i++)
{
data[i] = 0;
}
var remainingSamplingInterval = SamplingInterval - (DateTime.UtcNow - previousRead);
if (remainingSamplingInterval > TimeSpan.Zero)
{
HighResolutionTimer.Sleep((int)remainingSamplingInterval.TotalMilliseconds);
}
// Prepare for reading
try
{
// Measure required by host : pull down then pull up
pin.Write(false);
HighResolutionTimer.Sleep((decimal)WakeupInterval.TotalMilliseconds);
pin.Write(true);
// Read acknowledgement from DHT
pin.Wait(true, timeout);
pin.Wait(false, timeout);
// Read 40 bits output, or time-out
var cnt = 7;
var idx = 0;
for (var i = 0; i < 40; i++)
{
pin.Wait(true, timeout);
var start = DateTime.UtcNow;
pin.Wait(false, timeout);
// Determine whether bit is "1" or "0"
if (DateTime.UtcNow - start > bitSetUptime)
{
data[idx] |= (byte)(1 << cnt);
}
if (cnt == 0)
{
idx++; // next byte
cnt = 7; // restart at MSB
}
else
{
cnt--;
}
}
}
finally
{
// Prepare for next reading
previousRead = DateTime.UtcNow;
pin.Write(true);
}
var checkSum = data[0] + data[1] + data[2] + data[3];
if ((checkSum & 0xff) != data[4])
{
throw new InvalidChecksumException("Invalid checksum on DHT data", data[4], (checkSum & 0xff));
}
var sign = 1;
if ((data[2] & 0x80) != 0) // negative temperature
{
data[2] = (byte)(data[2] & 0x7F);
sign = -1;
}
var humidity = (data[0] << 8) + data[1];
var temperature = sign * ((data[2] << 8) + data[3]);
return(GetDhtData(temperature, humidity));
}