Any other way

[pdl]

Hi guys

is there any other way of doing this program.

[ckielstra]

[pdl]

I am trying to light an led with out a resistor and with out it flickering and turning ever now and again

Pete

[ckielstra]

I could give you ten possible suggestions for implementing such a function and than have you choose the single suggestion fitting your needs ...
... or you give more details about your system and requirements.

Because of my limited (spare) time you'll have to do with the last option. Also explain _why_ your example code is not sufficient.

[pdl]

Thank you for you help ckielstra as you can see by my code i am new to C.

The Led Flickers ever now and again

What i would like when the program sees 1.6ms and a bove the Led stays on until the pluse is no longer 1.6ms or greater.

its just not stable a the minute

Pete

[ckielstra]

I don't know the characteristics of your input signal, but most likely the waiting for a pulse is what causes your LED to flicker.

The easiest method to solve this is by removing the LED modulation out of the main loop. Create a timer driver interrupt which will drive your LED. Right now I don't have time to post example code but if you search this forum with the keywords 'soft PWM' you will find some related posts.

[pdl]

I have tried that

I tried to use some of this code but could not get it to work properly.

The input pulse is a 1ms to 2ms pulse the same type of pluse that drives a model servo.

thanks

Pete

#include <16F877.H>
#fuses XT, NOWDT, NOPROTECT, BROWNOUT, PUT, NOLVP
#use delay(clock = 4000000)

#define PWM_PIN PIN_B0

#define LOOPCNT 39

int8 width;

//-------------------------------
#INT_RTCC
void tick_interrupt(void);

//====================================
main()
{
width = 0;

setup_counters(RTCC_INTERNAL, RTCC_DIV_1);
enable_interrupts(INT_RTCC);
enable_interrupts(GLOBAL);

// Step through all values for width, from 0 to 39.
// This will slowly increase the duty cycle from 0 to 100%,
// by doing one step every 100 ms.
while(1)
{
for(width = 0; width <= LOOPCNT; width++)
delay_ms(100);
}

}

//====================================
#INT_RTCC
void tick_interrupt(void)
{
static int8 loop = LOOPCNT;
static int8 pulse;

if(--loop == 0)
{
loop = LOOPCNT;
pulse = width;
}

if(pulse)
{
output_high(PWM_PIN);
pulse--;
}
else
{
output_low(PWM_PIN);
}

}

[ckielstra]

[pdl]

Yes i changed the pic i was using

i tried to use some of this code with the pulse measurement code and i could not get it working

Pete

[ckielstra]

Try to be more detailed in your descriptions, just saying 'it's not working' is too limited. What do you expect to see, what is different and what behaviour do you actually see?

Are you using the PIC16F877 or the PIC16F877A? The first is very old...

Note that the PIC16F877 has two internal PWM hardware modules which are easier to use, will work more accurate and have less impact on the CPU usage than the soft PWM based on interrupts.

[pdl]

Hi ckielstra

I am using the 12f629

When i say it did not work i was putting a 1ms to 2 ms pulse in on PIN_A3 and was not getting anything out of PIN_A2 but looking at it now i think that the ICD was setup for MCLR and not I/O.


I expect For the LED to light when i put a 1.6ms pulse on PIN_A3
PIN_A2 should have a 100hz PWM output a 50% duty

When the input pulse is below 1.6ms the LED should stay turned off and not come on until the 1.6ms pulse is back on the input pin.

hope this a bit more clear

Pete

[SherpaDoug]

[pdl]

I am using a Mosfet as the LEDs i am using draw 350ma at 3.6v

Pete

[ckielstra]

Thanks for explaining your circuit in more detail. Now it makes more sense.

[pdl]

Here is my code so far i now can turn on some sort of PWM with my input which is 1ms to 2ms and the trip should be 1.6ms but i can not get the
timing right to get 100Hz 50% duty from the PWM pin


I have a Mosfet which i supply 7.4v to and with the 50%duty from the PWM i was hoping to get 3.7v output from the Mosfet.

thanks

Pete