private void ExpectLevel(GpioPinValue value, int milliseconds)
{
if (this.pin.PinMode != GpioPinDriveMode.Input)
{
this.pin.PinMode = GpioPinDriveMode.Input;
}
if (!pin.WaitForValue(value, milliseconds))
{
if (!pin.WaitForValue(value, milliseconds))
{
throw new SensorReadTimeoutException("等待" + value + " 读取DHT11 温度和湿度超时");
}
}
}
private THData TryGetMeasure()
{
//Prepare buffer to store measure and checksum
var data = new byte[5];
for (var i = 0; i < 5; i++)
{
data[i] = 0;
}
//Wait for sensor response
_pin.PinMode = GpioPinDriveMode.Input;
//Read acknowledgement from sensor
_pin.WaitForValue(GpioPinValue.High, 100);
_pin.WaitForValue(GpioPinValue.Low, 100);
//Read 40 bits to acquire:
//16 bit -> Humidity
//16 bit -> Temperature
//8 bit -> Checksum
var cnt = 7; //bit counter
var idx = 0; //bit index
var hrt = new HighResolutionTimer();
for (var i = 0; i < 40; i++)
{
hrt.Reset();
_pin.WaitForValue(GpioPinValue.High, 100);
hrt.Start();
_pin.WaitForValue(GpioPinValue.Low, 100);
hrt.Stop();
//Check if signal is 1 or 0
if (hrt.Elapsed > _bitDataTime)
{
data[idx] |= (byte)(1 << cnt);
}
if (cnt == 0)
{
idx++; //next bit
cnt = 7; //restart with next byte
}
else
{
cnt--;
}
}
var checkSum = data[0] + data[1] + data[2] + data[3];
if ((checkSum & 0xff) != data[4])
{
return(null);
}
var sign = 1;
//Check negative temperature
if ((data[2] & 0x80) != 0)
{
data[2] = (byte)(data[2] & 0x7F);
sign = -1;
}
return(new THData
{
HumidityPercentage = ((data[0] << 8) + data[1]) / 10,
TemperatureCelsius = (sign * ((data[2] << 8) + data[3])) / 10
});
}