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I'm building a weather station with two UNOs, using NRF24l01+ radios. Communications are fine. I'm sending a struct from one to the other. The struct has three elements:

    struct weather {
      float tempData;
      float humData;
      float pressData;
    };
    weather wData = {0, 0, 0};

I then populate the struct with values from my DHT22 Temperature Sensor and my BMP085 pressure sensor.

    float c = dht.readTemperature();
    wData.tempData = (c * 9/5) + 32;
    wData.humData = dht.readHumidity();

    sensors_event_t event;
    bmp.getEvent(&event);
    wData.pressData = (0.0295 * event.pressure);

Now I send it via the NRF24L01+.

    radio.write(&wData, sizeof(wData);

On the receiving Uno I have this.

    struct weather {
      float tempData;
      float humData;
      float pressData;
    };

    weather wData = {0, 0, 0};

    radio.read( &wData, sizeof(wData) );
    Serial.println(wData.tempData);
    Serial.println(wData.humData);
    Serial.println(wData.pressData);

I get results similar to this:

    Temp = 75.43
    Hum = 35.76
    Press = 0.00

The first two are correct. The final one is not. I can change the order and the first two will always be correct, but the last element is always 0.00. For example:

   Hum = 35.76
   Press = 30.14
   Temp = 0.00

I know I'm missing something here with my code but I can't find it. Anyone have some suggestions?

Gilles 'SO- stop being evil'
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brorobw
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1 Answers1

2

Modified my struct by changing the first two elements from float to int.

struct weather {
  int tempData;
  int humData;
  float pressData;
}
weather wData;

Everything transmits fine now. I don't really need the precision of a float for temperature and humidity. However, I would still like to find the problem. Could there be some problem with the size of three floats versus two ints and a float? Serial.print(sizeof(wData)) is 12 when all elements are floats and 8 when using two int and a float. My understanding is the NRF24L01+ has a transmit and receive buffer of 32 bytes.

brorobw
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