Andy A / SlowPWM

Very simple class to give slow speed PWM using timers and digital out.

Example use...

#include "SlowPWM.h"
SlowPWM MyTimer1(LED1);
SlowPWM MyTimer2(LED2);
SlowPWM MyTimer3(LED3);

main()
{
    MyTimer1.setPeriod(4);
    MyTimer1.setHighTime(2);
    MyTimer1.start();
    MyTimer2.setPeriod(2);
    MyTimer2.setHighTime(1.5);
    MyTimer2.start();
    MyTimer3.setPeriod(3.8);
    MyTimer3.setHighTime(1.5);
    MyTimer3.start();
    while(true) {
        wait(1);
    }
}

Files at this revision

API Documentation at this revision

Revision 2:c90e2d2f52aa, committed 2019-06-21

Comitter:
AndyA
Date:
Fri Jun 21 09:33:26 2019 +0000
Parent:
1:386d04fe1e37
Child:
3:3f7eb3ad23d4
Commit message:
Re-order constructor arguments.; Add special case handling for duty cycles of 0 or 1.; Stop now also cancels any scheduled turn off.

Changed in this revision

SlowPWM.cpp Show annotated file Show diff for this revision Revisions of this file
SlowPWM.h Show annotated file Show diff for this revision Revisions of this file 
--- a/SlowPWM.cpp	Tue Jun 18 16:22:56 2019 +0000
+++ b/SlowPWM.cpp	Fri Jun 21 09:33:26 2019 +0000
@@ -6,14 +6,14 @@
     _timeOn=0.5f;
 }
  
-SlowPWM::SlowPWM( float period, float highTime, const PinName pin ):DigitalOut(pin)
+SlowPWM::SlowPWM( const PinName pin, const float period, const float highTime ):DigitalOut(pin)
 {
     setPeriod(period);
     setHighTime(highTime);
     start();
 }
  
-void SlowPWM::setPeriod(float period)
+void SlowPWM::setPeriod(const float period)
 {
     _repeatTime = period;
     if (_repeatTime <= 0)   // check it's not 0 or negative
@@ -21,22 +21,30 @@
     setHighTime(_timeOn);  // perform sanity check on high time
 }
  
-void SlowPWM::setHighTime(float highTime)
+void SlowPWM::setHighTime(const float highTime)
 {
     _timeOn = highTime;
     if (_timeOn >= _repeatTime)  // check it's not more than the cycle time.
         _timeOn = _repeatTime/2; // set to 50% if invalid 
 }
  
-void SlowPWM::setDutyCycle(float cycle) {
-        if ((cycle >=0) && (cycle <=1)) {
+void SlowPWM::setDutyCycle(const float cycle) {
+        if (cycle == 1) {
+          stop();
+          write(1);
+          } else if (cycle == 0) {
+              stop();
+              write(0);
+        } else if ((cycle >0) && (cycle <1)) {
         _timeOn = _repeatTime*cycle; 
+        start();
         } else
         _timeOn = _repeatTime/2; // set to 50% if invalid 
 }
  
 void SlowPWM::stop()
 {
+    offTimer.detach();
     cycleTimer.detach();
 }
  

--- a/SlowPWM.h	Tue Jun 18 16:22:56 2019 +0000
+++ b/SlowPWM.h	Fri Jun 21 09:33:26 2019 +0000
@@ -2,6 +2,11 @@
 #define __SlowPWM_H__
  
 #include "mbed.h"
+
+
+/// A basic class to create very slow PWM signals using Digital IO and timers.
+/// If setting a period and high time then you must manually call start.
+/// If setting a duty cycle then it will start automatically, make sure you've set the peiod first if you care about it.
 class SlowPWM : public DigitalOut
 {
 public:
@@ -10,19 +15,18 @@
     SlowPWM( const PinName pin);
  
 // constructor that also starts things running
-    SlowPWM( float period, float highTime, const PinName pin );
+    SlowPWM( const PinName pin, const float period, const float highTime);
  
 // set the period
-    void setPeriod(float period);
+    void setPeriod(const float period);
  
 // set the on time per cycle
-    void setHighTime(float highTime);
+    void setHighTime(const float highTime);
 
 // set the on time per cycle as a fraction
-    void setDutyCycle(float cycle);
-
+    void setDutyCycle(const float cycle);
  
-// stop things. If output is high it will still turn low at the correct time
+// stop things. 
     void stop();
  
 // start things