/// <summary>
/// Gets a reading from the sensor.
/// </summary>
/// <returns>Returns an IDhtReading instance containing
/// the data from the sensor.</returns>
public async Task <IDhtReading> GetReadingAsync()
{
IDhtReading returnValue = new DhtReading();
if (this.ChangeReader != null)
{
try
{
// ***
// *** Clear and start the Change Reader.
// ***
this.ChangeReader.Clear();
this.ChangeReader.Start();
// ***
// *** Bring the line low for 18 ms (this is needed for the DHT11), the DHT22 does need
// *** need as long.
// ***
this.TriggerPin.Write(GpioPinValue.High);
await Task.Delay(TimeSpan.FromMilliseconds(18));
this.TriggerPin.Write(GpioPinValue.Low);
// ***
// *** Wait for 43 falling edges, but do not wait for more than the timeout.
// ***
CancellationTokenSource source = new CancellationTokenSource((int)this.Timeout.TotalMilliseconds);
await this.ChangeReader.WaitForItemsAsync(43).AsTask(source.Token);
// ***
// *** Get all of the change records.
// ***
IList <GpioChangeRecord> changeRecords = this.ChangeReader.GetAllItems();
// ***
// *** Convert the change records to the 5 bytes of data that the sensor
// *** sends out.
// ***
byte[] data = changeRecords.ToByteArray();
// ***
// *** Convert the 5 bytes of data to an IDhtReading instance.
// ***
returnValue = DhtReading.FromData(data);
}
catch (TaskCanceledException)
{
// ***
// *** The sensor did not respond to the
// *** data request.
// ***
returnValue = DhtReading.FromTimeout();
}
finally
{
this.ChangeReader.Stop();
}
}
else
{
throw new DhtNotInitializedException();
}
return(returnValue);
}
private IDhtReading GetReading()
{
Array.Clear(DataBuffer, 0, DataBuffer.Length);
// ***
// *** Bring the line low for 18 ms (this is needed for the DHT11), the DHT22 does need
// *** need as long.
// ***
pin.Write(GpioPinValue.Low);
SpinWaitPerformanceCounts(perf_counts_18ms);
pin.Write(GpioPinValue.High);
SpinWaitPerformanceCounts(perf_counts_40us);
pin.SetDriveMode(GpioPinDriveMode.Input);
SpinWaitPerformanceCounts(perf_counts_10us);
// ***
// *** Capture every falling edge until all bits are received or
// *** timeout occurs
// ***
var endTickCount = GetTickCount64() + ReadTimeout;
var previousValue = pin.Read();
var prevTime = 0L;
for (var i = -1; i < DataBufferBits;)
{
if (GetTickCount64() > endTickCount)
{
return(DhtReading.FromTimeout());
}
var value = pin.Read();
if ((previousValue == GpioPinValue.High) && (value == GpioPinValue.Low))
{
// ***
// *** A falling edge was detected
// ***
var now = PerformanceCounterValue;
if (i >= 0)
{
var difference = unchecked (now - prevTime);
if (difference > OneThreshold)
{
DataBuffer.SetBit(i);
}
}
prevTime = now;
++i;
}
previousValue = value;
}
// ***
// *** Convert the 5 bytes of data to an IDhtReading instance.
// ***
return(ParseData(DataBuffer));
}
