Question

What’s the best way to send float, double, and int16 over serial on Arduino?

The Serial.print() only sends values as ASCII encoded. But I want to send the values as bytes. Serial.write() accepts byte and bytearrays, but what’s the best way to convert the values to bytes?

I tried to cast an int16 to an byte*, without luck. I also used memcpy, but that uses to many CPU cycles. Arduino uses plain C/C++. It’s an ATmega328 microcontroller.

Answer 1

Yes, to send these numbers you have to first convert them to ASCII strings. If you are working with C, sprintf() is, IMO, the handiest way to do this conversion:

[Added later: AAAGHH! I forgot that for ints/longs, the function’s input argument wants to be unsigned. Likewise for the format string handed to sprintf(). So I changed it below. Sorry about my terrible oversight, which would have been a hard-to-find bug. Also, ulong makes it a little more general.]

char *
int2str( unsigned long num ) {
    static char retnum[21];       // Enough for 20 digits plus NUL from a 64-bit uint.
    sprintf( retnum, "%ul", num );
    return retnum;
}

And similar for floats and doubles. The code doing the conversion has be known in advance. It has to be told – what kind of an entity it’s converting, so you might end up with functions char *float2str( float float_num) and char *dbl2str( double dblnum).

You’ll get a NUL-terminated left-adjusted (no leading blanks or zeroes) character string out of the conversion.

You can do the conversion anywhere/anyhow you like; these functions are just illustrations.