python - Using Raspberry Pi to Receive Float from Arduino using NRF24L01 -

i've been learning on how transfer data arduino raspberry pi wirelessly using nrf24l01 based on following reference: raspberry pi 3 tutorial 14 – wireless pi arduino communication nrf24l01+.

the reason why want log temperature , humidity data wirelessly using dht22 sensors.

the arduino code shown below:

//sendreceive.ino  #include<spi.h> #include<rf24.h>  // ce, csn pins rf24 radio(9, 10);  void setup(void){     while(!serial);     serial.begin(9600);      radio.begin();     radio.setpalevel(rf24_pa_max);     radio.setchannel(0x76);     radio.openwritingpipe(0xf0f0f0f0e1ll);     const uint64_t pipe = (0xe8e8f0f0e1ll);     radio.openreadingpipe(1, pipe);      radio.enabledynamicpayloads();     radio.powerup();  }  void loop(void){     radio.startlistening();     serial.println("starting loop. radio on.");     char receivedmessage[32] = {0};     if(radio.available()){         radio.read(receivedmessage, sizeof(receivedmessage));         serial.println(receivedmessage);         serial.println("turning off radio.");         radio.stoplistening();          string stringmessage(receivedmessage);          if(stringmessage == "getstring"){             serial.println("looks want string!");             const char text[] = "yo wassup, haha";             radio.write(text, sizeof(text));             serial.println("we sent our message.");         }     }     delay(100);  } 

meanwhile, raspberry pi code shown below:

import rpi.gpio gpio lib_nrf24 import nrf24 import time import spidev  gpio.setmode(gpio.bcm)  pipes = [[0xe8, 0xe8, 0xf0, 0xf0, 0xe1], [0xf0, 0xf0, 0xf0, 0xf0, 0xe1]]  radio = nrf24(gpio, spidev.spidev()) radio.begin(0, 17)  radio.setpayloadsize(32) radio.setchannel(0x76) radio.setdatarate(nrf24.br_1mbps) radio.setpalevel(nrf24.pa_min)  radio.setautoack(true) radio.enabledynamicpayloads() radio.enableackpayload()  radio.openwritingpipe(pipes[0]) radio.openreadingpipe(1, pipes[1]) radio.printdetails() # radio.startlistening()  message = list("getstring") while len(message) < 32:     message.append(0)  while(1):     start = time.time()     radio.write(message)     print("sent message: {}".format(message))     radio.startlistening()      while not radio.available(0):         time.sleep(1 / 100)         if time.time() - start > 2:             print("timed out.")             break      receivedmessage = []     radio.read(receivedmessage, radio.getdynamicpayloadsize())     print("received: {}".format(receivedmessage))      print("translating receivedmessage unicode characters")     string = ""     n in receivedmessage:         # decode standard unicode set         if (n >= 32 , n <= 126):             string += chr(n)     print("out received message decodes to: {}".format(string))      radio.stoplistening()     time.sleep(1) 

based on arduino code above, code shows data transmitted shown below:

const char text[] = "yo wassup, haha"; 

based on raspberry code above, codes decode received data arduino shown below:

for n in receivedmessage:     # decode standard unicode set     if (n >= 32 , n <= 126):         string += chr(n) 

however, these decoding code works if transmit string or integer arduino raspberry pi. doesn't work if transmit float. since dht22 records temperature , humidity until 1 decimal point, required me transmit float. can here please teach me how decode float values?

you need convert float value string, , send string through radio.write function.

i'm not c++ specialist, this answer mentions std::to_string() function converts more or less c++ string. if need char[] instead, that answer provides c-style function job (well, put in function):

char buffer[64]; int ret = snprintf(buffer, sizeof buffer, "%f", myfloat);  if (ret < 0) {     return exit_failure; } if (ret > sizeof buffer) {     /* result truncated - resize buffer , retry. } 

on python side, if you're buffer msg contains float value (that is, you're data received received), call float(msg).

wiki