Here's an other method:

// all times are long given in ms 
const long INTERVAL = 1000/frequency_in_Hz;
if( (current_time / INTERVAL)>(last_time/INTERVAL))
{
 sendUpdate();
 last_time = current_time;
}

This ensures that you sends at most X, equally spaced, updates per second, but less if your performances drops for some reasons.

Here's an other method:

// all times are long given in ms 
const long INTERVAL = 1000/frequency_in_Hz;
if( (current_time / INTERVAL)>(last_time/INTERVAL))
{
 sendUpdate();
 last_time = current_time;
}

This ensures that you sends at most X, equally spaced, updates per second, but less if your performances drops for some reasons.