Creates square-wave frequency output on pin p22. Custom frequency between 1Hz and 48 MHz. (LPC 1768)
Creates square-wave frequency output on pin22 with custom frequency.
Tested for frequencies from 1Hz to 48MHz. The accuracy depends heavily on the frequency - at 12, 24, 48 MHz the frequency deviation is less than 1%, but at 20 MHz it is about 20%.
Uses Library FastPWM ( http://mbed.org/users/Sissors/code/FastPWM/ ). For LPC 1768.
How to use this Library:
#include "mbed.h" #include "PwmOscillator.h" PwmOscillator oscillator; DigitalOut led1(LED1); int main() { oscillator.initWithFrequency(8000000); // initialize oscillator instance (pin p22) with custom frequency, here: 8MHz led1=1; // optional: indicator LED shows that oscillator is running oscillator.start(); // start oscillator wait(5); // optional: oscillator is running 5 seconds oscillator.stop(); // stop oscillator led1=0; }
PwmOscillator.cpp
- Committer:
- geotec
- Date:
- 2012-12-14
- Revision:
- 2:d9fea7c1fc8d
- Parent:
- 0:9e0f295a55a4
File content as of revision 2:d9fea7c1fc8d:
#include "mbed.h" #include "PwmOscillator.h" #include "FastPWM.h" FastPWM pinOut(p22); double _period_us = 0; double _pulsewidth_us = 0; void PwmOscillator::initWithFrequency(int frequencyHz) { _period_us = (1.0 / (double)frequencyHz)*1000000; _pulsewidth_us = _period_us / 2.0; pinOut.period_us(_period_us); } void PwmOscillator::start() { pinOut.pulsewidth_us(_pulsewidth_us); } void PwmOscillator::stop() { pinOut = 0; }