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Duddimobile
(@duddimobile)
New Member
Joined: 2 months ago
Posts: 2
2020-06-09 10:02 am  

Hi there,

I want to try to use the joystick demo from the article about nRF24L01+ wireless module using the ReliableDatagram from RadioHead. Instead of the joystick i want to use a DHT11 temperature and humidity sensor and send the data to the server (receiver).

The problem I face is that values from the joystick are integers but im reading floats from the DHT sensor.
What should I use instead of the 8-bit unsigned integer array (uint8_t) to send the values correctly?


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ROGUE
(@rogue)
Active Member
Joined: 3 months ago
Posts: 12
2020-06-09 3:24 pm  

Hi duddimobile,

got the same problem, there are a two solutions: one simple, just to get it work (that may not satisfy you at all) just leave the decimals. In my project I used three DHT11-sensors (stacked near beside in a beadboard for testing purposes) ...the values differed by 2°C and up to 4% huminity, so I think they are not that precise. That may be a good reason to forget the decimals. Next, not that simple is to split the DHT11-values into two parts integer and decimal, TX them and put them together in the RX-unit for display. (! Keep in mind that temperature can be minus! - that's another problem that has to be solved.)

Hope it will be fun to puzzle that out yourself! Hope this will be helpful.


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ROGUE
(@rogue)
Active Member
Joined: 3 months ago
Posts: 12
2020-06-11 12:31 am  

Hi again, forgot to say something important... the transmission can be done (usualy) by (ASCII-)caracters... therfore the uint8_t-value-space (0-255), of cause you can convert each number of the value into a char (including the negative-sign) and send them seperately... i.e. for the temperature value of -24,25 send: '-', '2', '4', '.', '2', '5' if you just want to display them on RX that's OK. Of cause you have to convert the chars to a float to do calculations like a trend or the average


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frogandtoad
(@frogandtoad)
Reputable Member
Joined: 1 year ago
Posts: 455
2020-06-11 1:43 pm  

@rogue

There is an easier way 😉

void setup() {
  Serial.begin(9600);

  float sensorValue = -1.0912345;
  byte decimalPlaces = 3; // IIRC... Max dp == 6

  // First, convert to string...
  String data = String(sensorValue, decimalPlaces);

  // At the recieving end of the nRF24L01...
  // Convert it back to a float and perform calculations if necessary.
  float floatReceieved = data.toFloat();
 }

Cheers!


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ROGUE
(@rogue)
Active Member
Joined: 3 months ago
Posts: 12
2020-06-17 4:13 am  

Hi frogandtoad, this is a nice hint. I will try that, next time when I do any serial communication with floats. Thanks!


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frogandtoad
(@frogandtoad)
Reputable Member
Joined: 1 year ago
Posts: 455
2020-06-18 8:39 am  
Posted by: @rogue

Hi frogandtoad, this is a nice hint. I will try that, next time when I do any serial communication with floats. Thanks!

You're welcome!

Let us know how you go 🙂


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