RF 433 Module with VirtualWire: transmit and receive using the same Arduino board

Question

I was wondering if it was possible to work, in the same Arduino board, both Transmitter and Receiver RF 433 MHz modules. Is it feasible?

Here is the schematics I tried:

1) a pushbutton toggles a state value (0 or 1) and triggers the RF transmitter to send it as a message to the receiver module

2) the RF receiver, whenever reading the message, turns on or off a LED according to the corresponding value (0 or 1)

Here is the source code I wrote:

#include <VirtualWire.h>

#define BTN_PIN A0    // pushbutton que aciona a transmissao
#define LED_PIN 13    // LED aceso ao receber o sinal
#define TX_PIN   4    // ligado ao pino DATA do transmissor RF
#define RX_PIN   7    // ligado ao pino DATA do receptor RF

#define SPEED  5000   // velocidade de comunicacao (bits por segundo)

int estado = 0;

void setup() {
  pinMode(BTN_PIN, INPUT);
  pinMode(LED_PIN, OUTPUT);

  vw_set_tx_pin(TX_PIN);  // transmissor
  vw_set_rx_pin(RX_PIN);  // receptor
  vw_setup(SPEED);
  vw_rx_start();

  Serial.begin(9600);
}

void loop() {
  int pressionado = !digitalRead(BTN_PIN);
  char msg[4];

  if (pressionado) {
    estado = !estado;
    itoa(estado, msg, 10);

    vw_send((uint8_t *) msg, strlen(msg));
    vw_wait_tx();

    Serial.print("Mensagem enviada: [");
    Serial.print(msg);
    Serial.println("]");

    delay(500);
  }

  uint8_t buf[VW_MAX_MESSAGE_LEN];
  uint8_t buflen = VW_MAX_MESSAGE_LEN;
  int recebido = 0;

  memset(msg, 0, 4);
  if (vw_get_message(buf, &buflen)) {

    for (int i = 0; i < buflen; i++)
      msg[i] = char(buf[i]);
    msg[buflen] = '\0';

    Serial.print("Mensagem recebida: [");
    Serial.print(msg);
    Serial.println("]");

    recebido = atoi(msg);

    Serial.print("recebido = ");
    Serial.println(recebido);

    digitalWrite(LED_PIN, recebido);
  }
}

When I run it, according to Serial Monitor it sends the message. The problem is no message comes to the RF receiver.

Does anyone have an idea of what could be wrong?

Answer 1

As said in the comment you definitely need an antenna on both modules.

It is also possible that you are not supplying enough power to the 433 Mhz modules. The Arduino is not capable of outputting much current and RF transmitters generally have large current spikes.

So I would recommend that you use a seperate power supply to power the modules (do not forget to keep common ground between the Arduino and the Transmitter.)

I have also heard that it is preferred to not maintain common ground between the transmitter and the receiver. So if all else fails then use two separate power supplies.

Answer 2

These lines in the ISR in VirtualWire.cpp

    if (vw_rx_enabled && !vw_tx_enabled)
        vw_rx_sample = vw_digitalRead_rx() ^ vw_rx_inverted;

and

    if (vw_rx_enabled && !vw_tx_enabled)
        vw_pll();

mean that the receive path code is just not executed while the transmitter is enabled.

It kind of seems from the comment as that might not have been true at some point in the past, though I'm not seeing a version history for an "official" version to check.

You could try to modify the code to implement both, but it is worth noting that VirtualWire has been deprecated in favor of the more versatile RadioHead, so you might want to evaluate that and perhaps make modifications there instead.