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stewlg

Member Since 01 Mar 2014
Offline Last Active Jun 10 2014 02:38 PM

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#57248 Netduino NRPE monitor

Posted by stewlg on 01 April 2014 - 04:58 AM

Full post here:

http://www.skyscratc...r-for-netduino/

Mario Vernari likes this

#56717 DHT11/22 sensor managed driver

Posted by stewlg on 09 March 2014 - 12:09 AM

I was getting the

DHT sensor Read() ok, RH = 0.0%, Temp = 0.0�C 32.0�F

behavior with my DHT22 and a Netduino Plus 2 until I disconnected and reconnected a pin. Then I tried Fred Werneck's previous suggestion and changed DhtSensor.cs's Read() function to this:

        public bool Read()
        {
            if (disposed)
            {
                throw new ObjectDisposedException();
            }
            // The 'bitMask' also serves as edge counter: data bit edges plus
            // extra ones at the beginning of the communication (presence pulse).
            bitMask = 1L << 41;

            data = 0;
            // lastTicks = 0; // This is not really needed, we measure duration
            // between edges and the first three values are ignored anyway.

            // Initiate communication
            portOut.Active = true;
            portOut.Write(false);       // Pull bus low
            Thread.Sleep(StartDelay);
            portIn.EnableInterrupt();   // Turn on the receiver
            portOut.Active = false;     // Release bus

            bool dataValid = false;

            // Now the interrupt handler is getting called on each falling edge.
            // The communication takes up to 5 ms, but the interrupt handler managed
            // code takes longer to execute than is the duration of sensor pulse
            // (interrupts are queued), so we must wait for the last one to finish
            // and signal completion. 20 ms should be enough, 50 ms is safe.
            if (dataReceived.WaitOne(50, false))
            {
                // TODO: Use two short-s ?
                bytes[0] = (byte)((data >> 32) & 0xFF);
                bytes[1] = (byte)((data >> 24) & 0xFF);
                bytes[2] = (byte)((data >> 16) & 0xFF);
                bytes[3] = (byte)((data >> 8) & 0xFF);

                byte checksum = (byte)(bytes[0] + bytes[1] + bytes[2] + bytes[3]);
                if (checksum == (byte)(data & 0xFF))
                {
                    dataValid = true;
                    if (bytes[0] == 0)
                    {
                        portIn.DisableInterrupt();
                    }
                    else
                    {
                        Convert(bytes);
                    }
                }
                else
                {
                    Debug.Print("DHT sensor data has invalid checksum.");
                }
            }
            else
            {
                portIn.DisableInterrupt();  // Stop receiver
                Debug.Print("DHT sensor data timeout.");  // TODO: TimeoutException?
            }
            return dataValid;
        }

Now I get this when the demo app starts up:

DHT sensor data timeout.
DHT sensor Read() ok, RH = 0.0%, Temp = 0.0�C 32.0�F
DHT sensor Read() ok, RH = 53.2%, Temp = 24.2�C 75.6�F
DHT sensor Read() ok, RH = 53.0%, Temp = 24.2�C 75.6�F
DHT sensor Read() ok, RH = 52.9%, Temp = 24.2�C 75.6�F
DHT sensor Read() ok, RH = 52.9%, Temp = 24.2�C 75.6�F
DHT sensor Read() ok, RH = 52.8%, Temp = 24.2�C 75.6�F

A timeout, one bad read, and then good ones from that point forward. I'm sure with a bit of work we could eliminate that first bad read as well, I haven't tried yet.

To save someone else time, I'm attaching my working project. I'm targeting the 4.3 framework successfully in it.