ISR and altering PWM output

Using Arduino Programming Questions
1

I am trying to get an interrupt that happens once every 5sec to alter the output of a PWM port. In the main loop the PWM is set to some value that is read from a POT. What I want is that if I set the PWM output to 50% continuously, but every 5 seconds the PWM goes to 100% output for 300ms then goes back to the POT value 50%. It keeps doing it as long as it is powered. The current code does not work as I want. Seems the ISR can't do heavy lifting like set a pin or alter the PWM 50% to 100%. So I tried whatever popped into my mind. Switch cases, if then....passing flags. I just can't get what I described above to work. I would appreciate any help.

I have an add on for later, it will have a SDcard logging feature but will worry about that later.
Thanks! Nick

#include <TimerOne.h>

// The code below allows the user to set the Preload current, Surge current and cycle time. This controls a dynamic motor brake platform to simulate motor momentary stall conditions  
// In normal operation the arduino generates a PWM steady state output, the ISR comes through periodically and generates a new current draw for a window of time then returning back to the preload current PWM setting.
// 

const int Drive = 6;
int SurgeFlag = 0;
int voltage;


void setup(void)
{
  pinMode(Drive, OUTPUT);
  Timer1.initialize(3000000);
  Timer1.attachInterrupt(Surge); 
  Serial.begin(9600);
}


// The interrupt will send a surge current 255 value to PWM. The surge frequency is controlled by the interrupt Timer1.initialize()

void Surge(void)
{
 SurgeFlag = SurgeFlag + 1;
 
}


// The main program will read ADC value and set PWM for preload current

void loop(void)
{
 
  noInterrupts();
  voltage = analogRead(A0);   // ADC reads 0 - 1023
  voltage = voltage/4;        // scale ADC 0 - 255 to set min/max PWM range
  analogWrite(Drive, voltage);
  interrupts();

  if (SurgeFlag == 1) {
  digitalWrite(6, HIGH);
  
  SurgeFlag = 0;
  delay(2000);
  
}

  

  
}
2

Variables shared with interrupt routines must be declared volatile. Furthermore, multibyte shared variables must be protected from corruption, when accessed by the main program, as follows:

noInterrupts();
int surge_copy = SurgeFlag;
interrupts();
...
if (surge_copy == 1) {

Use an 8 bit variable to avoid the above, if possible.

There is no need to disable interrupts for the analog read/write.

3

You can do this without using interrupts. Use milles to do your timing not delay(); Check blink without delay example.

4

Hi, I am interested in using the millis. I am trying my logic to work as following:

running all the time PWM A0- 10k pot set to 30%, every 2000ms I set the PWM to 100% for 300ms, then back to 30% in a loop. I have tried a lot of things and now my code is gibberish, scrapping it to start all over.

I like that Millis lets you drop through to the main C loop and not locked into a routine until finished. It will make saving the data to SD easy. I just can't wrap my head around how to use Millis for the timing described above. I would appreciate help with it.

5

Hi,

try this code

PS:
Hi,
Oops Sorry @macgman2000 it was a typo.
please correct:

unsigned long myTime1 = 0;
unsigned long myTime2 = 0;

// The code below allows the user to set the Preload current, Surge current and cycle time. This controls a dynamic motor brake platform to simulate motor momentary stall conditions
// In normal operation the arduino generates a PWM steady state output, the ISR comes through periodically and generates a new current draw for a window of time then returning back to the preload current PWM setting.
//
const int Drive = 6;
int voltage;
unsigned long myTime1 = 0;
unsigned long myTime2 = 0;
//------------------------------------------------------------------
void setup(void)
{
  pinMode(Drive, OUTPUT);
  Serial.begin(9600);
  myTime2 = millis();
}
//------------------------------------------------------------------
// The main program will read ADC value and set PWM for preload current
void loop(void)
{
  voltage = analogRead(A0);   // ADC reads 0 - 1023
  voltage = voltage / 4;      // scale ADC 0 - 255 to set min/max PWM range
  analogWrite(Drive, voltage);

  if (millis() - myTime2 >= 5000)       // If past 5 seg
  {
    myTime1 = millis();                 // Init mytime1
    while (millis() - myTime1 < 300)    // While myTime1 < 300 ms
    {
      analogWrite(Drive, 255);          // PWM max
    }
    myTime2 = millis();                 // Init mytime2
  }
}
6

Ah I see where I had tunnel vision. I was trying to force discrete if then. While would have done it. Thanks

7

Very weird problem came up. This only works for 4 or 5 passes through the inner 300ms loop then stops. The only thing responsive is A0 connected to a pot, I can vary it and it changes PWM output. Otherwise the 300ms stops executing the while loop.

8

Perhaps it is an overflow problem?
Are you using int? Best to use unsigned long

unsigned long myTime1 = 0; // etc
9

yes you are correct. It's been running longer than previously. I will watch it for a few hours to make sure it does not stop running. Thanks!

10

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