LED fading with PWM + Interrupt Timer

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Hi all, is that possible to implement timer interrupt to a LED fading PWM function?
microcontroller: 16F628A
compiler: MikroC

Objective:
LED fade in and out slowly by adjusting the PWM.
I had developed a code that working in this way
using timer so slowly increase the PWM duty cycle. However, it did not work out to be what i imagine.

The reason why i need this is because i need to insert this function into another program which able t change the PIC mode with LED blinking function (using interrupt timer as well).


My code is as below:
Code: 
signed int i = 0;
void InitTimer1() 
{
    T1CON = 0x31;
    TMR1IF_bit = 0;
    TMR1IE_bit = 1;
    INTCON = 0xC0; //
}
  void Interrupt() {
    if(TMR1IF_bit)
    {
     
      for(i = 0; i < 256; i += 10) // LED is glowing with delay by using timer
      {
       PWM1_Set_Duty(i);
      TMR1H = 0x4E; // set timer
     TMR1L = 0x20; // set timer
      }
      for(i = 250; i >= 0; i -= 10) // LED is fade out with delay by using timer
      {
       PWM1_Set_Duty(i);
      TMR1H = 0x4E; // set timer
     TMR1L = 0x20; // set timer
      }
      TMR1IF_bit = 0;// reset trigger bit
     }
     }

void main()
{
TRISB = 0x00;// B3 PWM output
PWM1_Init(5000);            // Initialize PWM frequency
//PWM1_Set_Duty(127);
PWM1_Start();

while (1) {


    }
}


Thank you.
 

Hi,

Don´t run lengthy loops within an ISR.

Without textual description and without knowing about your interrrupt interval timing, and the dimming timing...I don´t want to go deeper into your code.
Don´t make it unnecessary difficult for us to help.

Klaus
 
Give this code a try:
Code: 
/*
 * File: main_xc8.c
 * Target: PIC16F628A
 * Compiler: XC8 v1.45
 *
 * Description:
 *  Use the PWM output to fade an LED on and off.
 *
 *                     PIC16F628A
 *             +----------:_:----------+
 *        <> 1 : RA2               RA1 : 18 <>
 *        <> 2 : RA3               RA0 : 17 <>
 *        <> 3 : RA4(*)       OSC1/RA7 : 16 <>
 *    VPP -> 4 : RA5/VPP      OSC2/RA6 : 15 <>
 *    GND -> 5 : VSS               VDD : 14 <- 5v0
 *        <> 6 : RB0           PGD/RB7 : 13 <> PGD
 *        <> 7 : RB1/RX/DT     PGC/RB6 : 12 <> PGC
 *        <> 8 : RB2/RX/CK         RB5 : 11 <>
 *    LED <- 9 : RB3/CCP1      PGM/RB4 : 10 <>
 *             +-----------------------:
 *                      DIP-18
 * Notes:
 *  (*) RA4 is an open drain output. Requires an external pull-up for output.
 */
#include <xc.h>


// PIC16F628A Configuration Bit Settings
// CONFIG
#pragma config FOSC = INTOSCIO  // Oscillator Selection bits (INTOSC oscillator: I/O function on RA6/OSC2/CLKOUT pin, I/O function on RA7/OSC1/CLKIN)
#pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled)
#pragma config PWRTE = OFF      // Power-up Timer Enable bit (PWRT enabled)
#pragma config MCLRE = OFF      // RA5/MCLR/VPP Pin Function Select bit (RA5/MCLR/VPP pin function is digital input, MCLR internally tied to VDD)
#pragma config BOREN = OFF      // Brown-out Detect Enable bit (BOD enabled)
#pragma config LVP = OFF        // Low-Voltage Programming Enable bit (RB4/PGM pin has digital I/O function, HV on MCLR must be used for programming)
#pragma config CPD = OFF        // Data EE Memory Code Protection bit (Data memory code protection off)
#pragma config CP = OFF         // Flash Program Memory Code Protection bit (Code protection off)

#define _XTAL_FREQ 4000000ul

#define INTCON_T0IF_MASK    (1<<2)
#define CCP1_CCP1M_PWM_MODE (0b1100)
#define T2CON_TMR2ON_MASK   (1<<2)

void Init_PIC(void)
{
    // Diable all interrupts
    INTCON = 0;
    PIE1   = 0;
    OPTION_REG = 0b11111111;

    //Turn off comparitors
    CMCON = 0b00000111;

    //Set output default low:
    PORTA = 0;
    PORTB = 0;

    //Port A Data Direction
    TRISA = 0b00000000;

    //Port B Data Direction
    TRISB = 0b00000000;

}
//
// Setup CCP1 output for PWM at 5KHz
//
void Init_PWM(void)
{
    T2CON    = 0;                       // Stop TIMER2
    PR2      = ((_XTAL_FREQ/4)/5000)-1; // Set for 5KHz PWM
    CCP1CON  = 0;                       // Stop PWM
    CCPR1L   = 0;                       // Set duty cycle to 0%
    CCPR1H   = 0;
    CCP1CON  = CCP1_CCP1M_PWM_MODE;     // Select PWM mode
    T2CON    = T2CON_TMR2ON_MASK;       // Turn on TIMER2
}
//
// Setup TIMER0 to assert T0IF every 4096 instruction clock cycles
//
void Init_TIMER0(void)
{
    TMR0 = 0;
    // TIMER0 clock source is the internal instruction cycle clock (_XTAL_FREQ/4)
    // PRESCALER assigned to TIMER0
    // PRESCALE set to 1:16
    OPTION_REG &= 0b11010000;
    OPTION_REG |= 0b00000011;
    INTCON     &= ~INTCON_T0IF_MASK;
}

void main(void)
{
    unsigned char FadeDirection;
    Init_PIC();
    Init_PWM();
    Init_TIMER0();

    FadeDirection = 1;
    for(;;)
    {
        if (INTCON & INTCON_T0IF_MASK)
        {
            INTCON &= ~INTCON_T0IF_MASK;
            if (CCPR1L >= PR2)
            {
                FadeDirection = (unsigned char)(0-FadeDirection);
            }
            CCPR1L += FadeDirection;
        }
    }
}
I tried to write this code to be as portable as possible between XC8 and MikroC.

All you should need to do is delete the #include <xc.h> and #pragma statements.
 

HI Klaus, thanks for giving advice. sorry for my mistake. the timer value that i set is 360ms.
actually the timing do not need to be accurate. as long as can see the LED slowly fade in and out.
i just want to implement interrupt timer to PWM LED fading so that later on i can change state with button.
what i am trying to do is, the LED is slowly glowing and dimming by setting the PWM. I have no idea how can i do this without the loop.



Hi Dan, thanks for sharing your code.
I cant compile without the xc.h file. do you mind to share it?
and is your code is fading between all the LEDs that connect to the PIC output?
actually what i want is setting the PWM duty cycle by using timer. Is that possible to achieve?
because my final goal is that i will set my PIC into 3 different mode:
1st mode: LED blink with 300ms interval
2nd mode: LED blink with 800ms interval
3rd mode: LED slowly glow and dim.

so I need a timer interrupt to change between these 3 mode ( delay is not suitable).
i already done with first 2 mode. now only left PWM.
 

XC8.h is propriety information from Microchip but it's free to download as part of the XC8 compiler package (currently v1.45). However, what Dan1138 is suggesting is you can easily convert it to MikroC format. The XC8.h is just a cross reference list of port names and numbers and bit names and numbers. An equivalent must exist for MikroC so if you can substitute it the program should compile. If you can't find it's equivalent, the real XC8.h file will probably work if you download it.

Things to remember:
1. The PWM can be set to maximum for full brightness and minimum for 'off'.
2. The PWM generator is a hardware device, once you configure it, the PWM comes out and stays running unless you reset or configure it again.
3. Use a spare timer to generate long delays for "1st Mode and 2nd Mode", alternating between maximum and minimum to blink the LED.
4. For "3rd Mode" use each delay to step up to maximum PWM then down to minimum again in a loop. At each 'tick' you reconfigure the PWM for the next brightness step.

Brian.
 
There is a bug in my code.

This line:
Code: 
            if (CCPR1L >= PR2)
Should be replaced with this line:
Code: 
            if ((CCPR1L < 1) || (CCPR1L >= PR2))
 
I see solutions have already been provided. Although you should use arduino for fading. Its way easy to use than Pic MCU and you can use built in LED to observe the blinking and fading of LED in real time. It takes no time in getting programmed again and again.

Good Luck!
 
Syedhamzahasan - please don't suggest changing the product to solve the problem. If you think Arduino can replace a PIC, I challenge you to make an Arduino version of some of my PIC projects that use over 1Mb of memory and have to run at 64MHz. PIC is no better than Arduino, Arduino is no better than PIC but each has their own strengths and weaknesses, you have to respect that.

Brian.
 

Brian cool down man, if you read my post I haven't once mentioned the word "Better". Or compared Arduino and pic to be superior to one another. I merely said its user friendly and easy to perform small tasks such as Fading LEDs. My advance projects are all on PIC, but even if I'm making a complex robot using servos or something with small level automation or multiple LEDs, I go for Arduino immediately. If you can't get what I said than "peace".
 
Hi, Brian, thanks for your guide.
I am still trying on the code. will feedback here once i have any progress.


Dan1138 said:
There is a bug in my code.

This line:
Code: 
            if (CCPR1L >= PR2)
Should be replaced with this line:
Code: 
            if ((CCPR1L < 1) || (CCPR1L >= PR2))
Click to expand...

Hi thanks for your code. i will try it.


Hi, thank you very much for your advice. I do have Arduino Uno with me, just that I had made PIC board that comes with MOSFET so that i can use it to control higher voltage devices.



Hi, Brian, thank you very much for your guidance.
Seems like you have a lot of experience in PIC, do you mind to tell me if I want to use PIC to use multiple output to control device individually?
For example, 4 output LED that switch ON individually base on 4 sensor. In this case is it i need to use timer interrupt to scan all 4 inputs?
I still havent done any complicated coding for PIC. All the project that i did, those function is run in serial and a lot of them is using delay function.
 
Last edited:

Hi,

I think every microcontroller easily can handle this. It is a personal taste to work with timer interrupts or not.
My taste: I'd definitely use timer interrupts. A couple additiinal lines of code to set up the timer. But then it gives flexibility, deterministic results, exact timing (independent of how many channels are fading) ...

I'm working on an 8 channel light controller. Each channel with independent dimming, individual dimming-time-constant, individual value-to-brightness-curve, all in an 20ms loop, additionally a lot of communication (traffic) via two interfaces...
All on an AVR chip.

Klaus
 
Hi, Brian, thank you very much for your guidance.
Seems like you have a lot of experience in PIC, do you mind to tell me if I want to use PIC to use multiple output to control device individually?
Click to expand...
I've been using them since the General Instruments PIC1650 came out over 30 years ago. It was a forerunner of the first Microchip ICs with an almost identical processor core and instruction set. The first project was for industrial lighting control where a simple switch could control many distributed high power lights (1KW each) distributed across huge factories and warehouses where a single switch would be incapable of handling the power and surge sequencing.

As Klaus points out, almost all MCU have the ability to sense and produce several signals to the outside World and apparently simultaneously although they really only do one task at a time very quickly. The way I do it with PICs is to use a timer to generate interrupts, this put the timekeeping in the 'background' while the rest of the program carries on. In the timer interrupt routine (the ISR) I check if variables are zero or not and if they are above zero, I decrement them. This means each of the variables counts down from your desired starting value to zero then stops. To start a timer, just write a value to the variable, to see if the delay period has ended, just check if the variable is zero. You can run as many variables at the same time as you wish and they all work independently but count down at the same speed. For example, if you make the timer interrupt period 0.1 seconds, then load 25 into a counter variable, it will reach zero in 2.5 seconds. If at any time you wrote 83 to another variable, it would reach zero 8.3 seconds later and there would be no interaction between the two delays.

Brian.
 


Hi, thanks for all the guide and info.
but i still have doubt on the output state, because from what i know, PIC output is not latched.
for simple example, 3 sensors controlling 3 LEDs, when there is input, then the output must on.
how do you make all 3 LEDs constantly on if all 3 input is high.
 

Hi,

PIC output is not latched.
Click to expand...
There is a flip-flop at every output.
The software may switch the output to ON or OFF.

You may control as much outputs as you want independently. And you may read and process as many inputs as you like, independently.
Nothing special... done in almost any application.

I´m not familiar with PIC, but I assume there are instructions to modify a single bit of an output port. If not then keep the last wirtten value in SRAM and modifiy just the single bit you like using AND and OR instructions. For sure you write the complete byte, but only the bit_of_interest is modified.
Instead of keeping the last written value in SRAM you may RMW instructions or RMW functions.

Klaus
 
Indeed there are instructions. PIC devices have orthogonal instruction sets, the same instruction can be applied to any register, regardless of whether it is a memory or a port address. They don't have specific port bit instructions (in... out...) like some other MCU, you just set or reset a bit at the ports address.

Alpha91 - Once set, a bit remains set until you reset it. Your code turns it on, your code turns it off, it doesn't turn itself off when you move to the next instruction.

Brian.
 

Hi Klaust, for PIC, i can set single output. I just curious on how to maintain the output state. Brian had answered it.
Anyway, thank you very much for your guidance.


Brian, sorry that i havent test the output without changing it and proceed to next instruction.
so you mean even like PIC 16F628A or any other common PIC also same? the output remains until my code change it's state?
 

Hi,

so you mean even like PIC 16F628A or any other common PIC also same? the output remains until my code change it's state?
Click to expand...
Afaik this is the same with every microcontroller.

A quick view into a datasheet will give you this information.

Klaus
 
KlausST said:
Hi,


Afaik this is the same with every microcontroller.

A quick view into a datasheet will give you this information.

Klaus
Click to expand...

alright. sorry, i have one more question.
if my output require something like blink, like 500ms interval. so i need another timer for the blink? while i still want other output to work independently.
 

Afaik this is the same with every microcontroller.
Click to expand...
I think Klaus is correct.

For example:
PORTA |= 0x01; will OR the current port A value with 00000001 which turns the least significant bit ON.
PORTA &= 0xFE; will AND the current port A value with 11111110 which turns the least significant bit OFF.

it stays that way until another instruction changes it.

Beware of RMW (Read Modify Write) problems with 10F, 12F and 16F series PICs if you copy my examples because the state of all the port pins is read in before writing the new value back. That isn't necessarily the same as reading back what you last wrote to the port - it is the present logic level it reads which might depend on external factors. A better method is to keep a copy of the port value in memory, modify it then write all the bits back to the port at once. On 18F series PICs, you don't have to do that but you should write output values to the LAT registers instead of the port.

Brian.
 

Alright. I had tested the PIC output and it is exactly like what you said. It did not change its state until the code ask it to do so. Thanks for your info.
I see. so you recommend me to read the PORT and write the whole PORT instead on setting the pin one by one during changing state?

and also i have one more question on timer application below:
alright. sorry, i have one more question.
if my output require something like blink, like 500ms interval. so i need another timer for the blink? while i still want other output to work independently.
Click to expand...

is my concept correct in this case?
 

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