Radiohead checking simple received radio data problem 433mhz

Projects Networking, Protocols, and Devices
1

I'm trying to set up a basic 1 way link between two Uno's.

The transmitting Uno sends a simple word or character which should be recognised on the receiving Uno in order to perform some command. Using "Hello World" gave an odd extra character. Smaller / 1 character long messages don't have an extra strange character.

The idea is that a relay will either turn on or off by command.

I'm sure that I'm going wrong somewhere - the message is never confirmed on the receiving Uno.

Transmitter Uno Code: (DHT22 part isn't doing anything much at the moment.)

#include <RH_ASK.h>
#include <SPI.h> // Not actually used but needed to compile
#include "DHT.h"

#define DHTPIN 2     // what pin we're connected to
#define DHTTYPE DHT22   // DHT 22  (AM2302)

RH_ASK driver;

int maxHum = 60;
int maxTemp = 40;

DHT dht(DHTPIN, DHTTYPE);

void setup()
{
    Serial.begin(9600);    // Debugging only
    if (!driver.init())
         Serial.println("init failed");
           dht.begin();
}

void loop()
{
    const char *msg = "A";
    driver.send((uint8_t *)msg, strlen(msg));
    driver.waitPacketSent();
    delay(2000);

// Reading temperature or humidity takes about 250 milliseconds!
  // Sensor readings may also be up to 2 seconds 'old' (its a very slow sensor)
  float h = dht.readHumidity();
  // Read temperature as Celsius
  float t = dht.readTemperature();
  
  // Check if any reads failed and exit early (to try again).
  if (isnan(h) || isnan(t)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }
  
    Serial.print("Humidity: "); 
  Serial.print(h);
  Serial.print(" %\t");
  Serial.print("Temperature: "); 
  Serial.print(t);
  Serial.println(" *C ");
  
}

Receiving Uno Code:

#include <RH_ASK.h>
#include <SPI.h> // Not actualy used but needed to compile

RH_ASK driver;

void setup()
{
    Serial.begin(9600);  // Debugging only
    if (!driver.init())
         Serial.println("init failed");
}

void loop()
{

  
    uint8_t buf[12];
    uint8_t buflen = sizeof(buf);
    if (driver.recv(buf, &buflen)) // Non-blocking
    {
      int i;
      // Message with a good checksum received, dump it.
      Serial.println((char*)buf);         
    }
    if (((char*)buf) == "A") {
    Serial.println("Message is confirmed as A");
    }    else {
    Serial.println("Something is wrong - confirmation did not work...");
    }
}

Thanks for reading :slight_smile:

2 
    if (((char*)buf) == "A") {

First, buf is NOT a NULL terminated array of chars. Second, this is NOT how to compare strings.

You MUST NULL terminate buff and you MUST use strcmp() to compare strings.

3

Try something like this (untested):

if (driver.recv(buf, &buflen)) // Non-blocking
    {
      buf[buflen]=0;
      // Message with a good checksum received, dump it.
      Serial.println((char*)buf);         
      if (buf[0] == 'A') 
         {
         Serial.println("Message is confirmed as A");
          }    
         else  
         {
         Serial.println("Something is wrong - confirmation did not work...");
          }
    }
4

Try something like this (untested):

Which won't solve OP's problem which involves strings longer than 1 character.