Wireless Question

Using Arduino Programming Questions
1

Hi. Have a question re wireless messaging. I am sending the char 'A' from the TX board to the RX board using the following code:

vw_send((uint8_t *)c, 1); // Turn buzzer on...Transmit the character 'c' to RX board

c is set to 'A', ie c = 'A' in the setup part of the file

I am receiving the message on the RX board with the following code:

uint8_t buflen = VW_MAX_MESSAGE_LEN;// Defines maximum length of message
uint8_t buf[buflen]; // Create array to hold the data; defines buffer that holds the message
if(vw_get_message(buf, &buflen)) // &buflen is the actual length of the received message; the message is placed in the buffer 'buf'

I am sending just this one character 'A'. On the receiving end, on the serial monitor I print out
the loop counter i, ie (i=0,i<buflen,i++), buf[0] and buf
I get the following
i = 0
buf[0] = 255 buf = y with two tiny dots on top of the y
I was expecting to get A. Not sure what 255 is (isn't ascii for A) or the y with two dots is...Also baffled why i would get different outputs for buf[0] and buf when i =0 anyway.
using virtualwire library and the 433Mhz WL RF Transmitter + Receiver Module Link Kit for Arduino/ARM/MCU Wireless
Any suggestions what I might try would be greatly appreciated.

2

y with two tiny dots on top of the y

aka -1

Post your code.
Use code tags.

Not sure what 255 is

Being an eight bit number, it isn't ASCII for anything.

3

IBM PC code page 437, character 0x00FF, codes for "y" with two dots over it.

4

I think this might have generated a warning because c is, presumably, not a pointer.

vw_send((uint8_t *)c, 1);

Anyway, I think it should be this:

vw_send((uint8_t *)&c, 1);

Pete

5

Thanks for the replies...Pete. I'm using code straight from a working project from HumanHardDrive (Arduino Tutorial Lesson #12: Wireless Communication) for the wireless code. In his project he prompts for c on the TX side (1 or 0), then sends it to the RX....On mine I am sending the character without asking for it on a prompt.

I'm perplexed when I print out buf[0] on the RX side and get a different output than with buf when I is 0 too. shouldn't they be the same?

6

changed code from Serial.println((char) buf[ii]; to Serial.println(buf_; now both buf[0] and buf show 255 on the printout. Forgot we added the (char) element trying to troubleshoot. Apologies._
*Does anyone know why 255 shows up instead the character 'A' I'm sending? *
I guess I could use 255 in my if statement, ie if(buf == 255); instead of if(buf == 'A'); but that doesn't satisfy my need to understand what's happening and have any confidence in the result.
Thanks for your help.

7

crojai:
I'm perplexed when I print out buf[0] on the RX side and get a different output than with buf when I is 0 too. shouldn't they be the same?[/quote]
No. buff[0] is the first unsigned character in the buffer array. Since it is unsigned (not just 'char') it is displayed as a decimal integer: 255. 'buff' is a character pointer, a.k.a. character string, apparently of length 1. The string contains a character of value 255 which displays as the ÿ.

8

John. I now see what the 255 signifies. If I'm not mistaken 255 is the larger integer which can be stored in an 8 bit word. Am I correct?

So I am sending the character A to the RX. I added the statement vw_have_message to confirm a message was received on the RX side. It does receive a message. But don't know why when I print out buf[0] on the serial monitor I get the 8 bit word max of 255 vs the actual message sent which is the character A.

 if(vw_have_message() == 1) // Satement added by virtualwire library recommendation as one of three statements to use before the get_message statement below// not in original HumanHardDrive code
    {
      Serial.println("Message has been received");
    }

    if(vw_get_message(buf, &buflen)) // &buflen is the actual length of the received message; the message is placed in the buffer 'buf'

    {
      Serial.print("buflen from &buflen = ");
      Serial.println(buflen); // Print out the buffer length derived from the &buflen above
      
      for(int i = 0;i < buflen;i++)
      {
        Serial.print("i = ");
        Serial.println(i);
        Serial.print(" buf[0] = ");
        Serial.print(buf[0]);
        Serial.print("   buf[i] = ");
        Serial.println(buf[i]);
 
        
        if(buf[i] == 'A')   <--- why not recognized???

Very puzzled. Bit lost here.

9

It's impossible to be sure because you didn't include some of the vital parts of your code, like the declarations, but I think el_supremo probably got it right in Reply #3. Did you try his suggestion?

10

Thanks for the suggestion. I didn't try it because I am using the exact same syntax as a working program in a related tutorial did for that statement. The only declarations I use related to the vx_send(... statement

vw_send((uint8_t *)c, 1);

[\code]

are

char c; and

c = 'A'; in void setup()

Thanks for taking the time to reply.
11

Just a suggestion...
If you are using Virtualwire, try the Tx and Rx examples in the library itself.
Just make sure your Tx and Rx pins match the examples.

12

I also agree with el_supremo and johnwasser. Unless you have a pointer, you need the & (address of) operator.

Try this example of the standard VW send sketch and see the difference between the two forms.

#include <VirtualWire.h>

void setup()
{
    Serial.begin(9600);  // Debugging only
    Serial.println("setup");

   
    vw_setup(2000); // Bits per sec
}

void loop()
{
 
    //const char *msg = "hello";
    char c;
    c = 'A';

    digitalWrite(13, true); // Flash a light to show transmitting
   // vw_send((uint8_t *)c,1);
    vw_send((uint8_t *)&c, 1);
    vw_wait_tx(); // Wait until the whole message is gone
    digitalWrite(13, false);
    delay(200);
}

Please post the code from your link actually using

char c;
c = 'A';
vw_send((uint8_t *)c, 1);
13

Thanks so much guys...this gives me something to try...waiting for another uno module to try it...hope it comes soon...