I'm learning Arduino's world, but knowing very little about C and C++.

I'm trying to achieve a little RF transmitter which should send the temperature and humidity from a DHT-11 sensor to a Raspberry Pi.

I'm using the RCSwitch library to send information with the Arduino, and the 433Utils library to receive it on the RPI.

Using those 2 libraries demos, I was able to send an integer, holding temperature or humidity information (mySwitch.send("00001010");), and read it on the RPI.

But how can I send both informations so that the RPI will know which one is the temperature and the humidity ?

I know I could just send both and assume the lowest is the temperature, but this would be very messy and not very rewarding.


Following Edgar's answer in https://arduino.stackexchange.com/a/52992/11604, I know write:

void send_string(const char *str){
    int i = 0;
    for (char *p = str; *p; p++ ) {     
        mySwitch.send((i<<8) + *p, 16);

void loop() {   
    String x = "$H" + String(h) + "T" + String(t) + "HI" + String(hic); 

Works perfectly ! (see his complete answer for the RPI-side code)

  • 1
    mySwitch.send("T45H50");, mySwitch.send("[45;50]");, mySwitch.send("T45"); mySwitch.send("H50");... – Juraj Aug 21 '18 at 19:31
  • Are you really sending an integer, or are you sending an ASCII representation of the binary bits of an integer? – Majenko Aug 21 '18 at 21:31
  • The send() method take either an integer, a string byte representation or a tri-state code, I cannot send a string directly – Dan Chaltiel Aug 22 '18 at 6:30

The library you have chosen is not designed for transmitting information between nodes. It is intended for sending simple ON/OFF commands to RF-connected switches. Bending it to send data in the way you want would be difficult. Not impossible, but difficult.

Instead you should be considering a more suitable system, such as the popular RadioHead library. It appears to have Raspberry Pi support out of the box:

Raspberry Pi Uses BCM2835 library for GPIO http://www.airspayce.com/mikem/bcm2835/ Currently works only with RH_NRF24 driver or other drivers that do not require interrupt support. Contributed by Mike Poublon.

Alternatively a small Arduino as an interface between the RF module and the Pi may be another option.

| improve this answer | |
  • I think this library is what I was looking for, thanks ! But I don't understand your last sentence, in what is this different than what I'm doing ? – Dan Chaltiel Aug 22 '18 at 6:35
  • Actually, RadioHead is far too complicated when you don't fully understand what you are doing (hope I'll get it someday). I found a very good answer with RCSwitch [arduino.stackexchange.com/questions/52989/…. – Dan Chaltiel Aug 22 '18 at 12:24

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