/// <summary>
/// Probe the sensor by reading pin data
/// </summary>
private void ReadPin()
{
IsUpdateSuccessful = false;
try
{
// Send the sensor our trigger signal
pin.Write(false);
// Wait at least 18ms for sensor initialization
Pi.Wait(20);
// Send the start signal
pin.Write(true);
// Wait 20μs - 40μs
Pi.WaitMicroseconds(30);
pin.Kind = PinKind.InputPullUp;
// Sensor should take over and go low
if (!pin.WaitLow(Pi.Microseconds(100)))
{
// FAIL: sensor did not take over
return;
}
// Wait for the sensor to switch to high
if (!pin.WaitHigh(Pi.Microseconds(100)))
{
// FAIL: sensor did not send high
return;
}
// Wait for sensor to begin data bits
if (!pin.WaitLow(Pi.Microseconds(100)))
{
// FAIL: sensor did not begin sending a data bit
return;
}
// Elapsed is the duration a data bit was held high
double elapsed = 0;
// A buffer for eight bits of data
byte data = 0;
// Now we can begin reading 40 data bits
for (int i = 0; i < 40; i++)
{
// Wait for the data bit
if (!pin.WaitHigh(Pi.Microseconds(100)))
{
// FAIL: no data bit was sent
return;
}
// Measure the data bit
if (!pin.WaitLow(Pi.Microseconds(100), out elapsed))
{
// FAIL: data bit was too long
return;
}
// Make room to store the next data bit
data <<= 1;
// If elapsed was more than 40µs then the data bit is 1
if (elapsed > 0.04d)
{
data |= 1;
}
// If 8 bits were read then copy those bits to our buffer
if (((i + 1) % 8) == 0)
{
buffer[i / 8] = data;
}
}
// Success is reached if the checksum passes
if ((buffer[4] == ((buffer[0] + buffer[1] + buffer[2] + buffer[3]) & 0xFF)))
{
IsUpdateSuccessful = (buffer[0] != 0) || (buffer[2] != 0);
}
}
finally
{
// Set pin to high and for next update
pin.Kind = PinKind.Output;
pin.Write(true);
// And set the last update time
lastUpdate = Pi.Now;
}
}