bunt _ / PwmOscillator

Creates square-wave frequency output on pin p22. Custom frequency between 1Hz and 48 MHz. (LPC 1768)

Dependencies:   FastPWM

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;
}

Diff: PwmOscillator.cpp

Revision:
0:9e0f295a55a4
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/PwmOscillator.cpp	Fri Dec 14 14:34:22 2012 +0000
@@ -0,0 +1,26 @@
+#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;
+}