VirtualWire confusions

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi all,
bit of an epic but I've tried to include all relevant info.

I bought a 4800bps 315Mhz RF link to have a play with..
http://www.coolcomponents.co.uk/catalog/product_info.php?cPath=25&products_id=186

Connecting one side to an Arduino Duemilanove and the other to an Arduino Nano - both 328

Assumed it was broken and was about to give up when I tried the VirtualWire Library http://www.open.com.au/mikem/arduino/ copied over the example code and got the things talking. :smiley:
My pleasure was somewhat diminished by my inability to understand the code or the helpfile.

This is the example sending code loop...

void loop()
{
const char *msg = "hello";
vw_send((uint8_t *)msg, strlen(msg));
delay(400);
}

Which from what I can piece together from forum and doc surfing sets the multi character constant called msg to have the string value hello and then uses the vw_send command from the library to send that text with a length of 5?
What does the (uint8_t *) part mean? Is it just standard for the send command? Multi-byte?

The receive loop code is...

void loop()
{
uint8_t buf[VW_MAX_MESSAGE_LEN];
uint8_t buflen = VW_MAX_MESSAGE_LEN;
if (vw_get_message(buf, &buflen)) // Non-blocking
{
int i;
// Message with a good checksum received, dump HEX
Serial.print("Got: ");
for (i = 0; i < buflen; i++)
{
Serial.print(buf[i], HEX);
Serial.print(" ");
}
Serial.println("");
}
}

uint8_t is new to me (as is most of this I'm afraid) Again, reading into it, it seems to be saying define a byte array with the length being the length of the string sent.
Then define another for the length itself.
Then checks to see if there is a message....
if there is, it runs through the array and displays it as a series of HEX characters.
(Actually it has helped to type this out so hopefully I have some of it correct!) :slight_smile:

Would appreciate if someone could check my understanding and comment please.

To take it a step further, I wanted to replace the HELLO message with the output from a pot connected to A0 (+5V and GND)
I mapped the reading to between 0 and 255 ...

analogValue = analogRead(0);  
analogValue = map(analogValue, 0, 1023, 0, 255);

...but then got completely confused when trying to amend the code to send this data.
It did give me some readings but these tended to be 0, 8 a few other randoms or 255. Also when the pot was turned all the way the output stopped completely so I guess that tx wasn't sending.

I'm using the default send and receive port for VirtualWire (12,11).
Should I have had a resistor connected to the pot?

Tried this as a send command...

vw_send((uint8_t *)analogValue, 1);

Where analogValue was the mapped int reading from the pot.

Then left most of the original code in the receive end but replaced the print line with.

Serial.println(buf[0], INT);

and took out the 'for' loop. Clearly wrong as it isn't giving me correct results.

Could someone assist please?

Many thanks in advance

2

Moved forwards slightly so thought it worth an update..

msg[0] = analogValue;

seems to put the INT value into char* msg for me (lying if I said I understood what was happening though. Stole it from some other code I found)

I can then vw_send this and pick it up at the far end.

If the value of analogValue is 0, nothing gets sent. Annoying but I can map to 1-255 in this case to prevent it as I don't need the accuracy.

Interesting I added the test code..

Serial.println(analogValue);
msg[0] = analogValue;

Serial.println(msg[0],DEC);

..to the sketch and analogValue counted from 0 - 255 and msg counted to 127 and then counted up from -128 to -1. Sure there is a good reason for this?

The number comes through correctly with the

for (i = 0; i < buflen; i++)
{
Serial.print(buf[i], DEC);
}

...receiving code however.

I guess I'm just getting in a knot with all the various data types :-[

3

I have managed to get this working. I blame my confusion over char* as I'd never used it before.