16f877 generate pwm according 2 analog input

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- 23rd December 2008, 19:48
madxice

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16f877 generate pwm according 2 analog input

Hello everybody,

I am trying to make buck converter and control it with 16f877. The logic is simple. If the output voltage of the buck is higher than reference voltage the pwm duty cycle will decrease, if the output voltage is lower than the reference the duty cycle will increase. It seems very simple, but I couldn't be able to write the program:( I write but i doesn't work. I am new at pic programming. Help me please!!!

My crystal is 20MHz.

And it gives an error " ADC conversion clock period (1e-7) is possible invalid for device clock frequency" in proteus simulation.

Code:

DEFINE OSC 20 DEFINE ADC_BITS 8 DEFINE ADC_SAMPLES 50 TRISA=%00000011 TRISB=00 TRISC=00 TRISD=00 TRISE=00 Reference var byte Voltage var byte CCP1CON=%000011100 CCP2CON=%000011100 T2CON=%00000101 'timer 2 on, 1:1 postscale, 1:4 prescale PR2= 49 CCPR1L=%00011001 get_reference: ADCON1=%00000000 ' Set LEFT Justification ' Enable ALL ADC's (using PIC16F87x as example) ADCON0=%11000001 ' Set ADC Channel 0 (RA0/AN0) ' Enable ADC Module PauseUS 50 ' 50uS Pause to allow sampling Capacitor to charge ADCON0.1=1 ' Start Conversion While ADCON0.1=1:Wend ' Wait for conversion to complete Reference=ADRESH ' Read 8-bit Result return get_voltage: ADCON0=%11001001 ' Set Fosc/32 ' Set ADC Channel 1 (RA1/AN1) ' Enable ADC Module PauseUS 50 ADCON0.1=1 While ADCON0.1=1:Wend Voltage=ADRESH return azalt: CCPR1L=CCPR1L-1 return arttir: CCPR1L=CCPR1L+1 return sabit: CCPR1L=CCPR1L return main_loop: Gosub get_Reference ' Get reference value Gosub get_voltage ' Get voltage value if Reference>Voltage then azalt if Reference< Voltage then arttir IF Reference=Voltage then sabit goto main_loop ' Do it forever end
- 23rd December 2008, 22:32
mackrackit

Welcome to the forum.

First thing I see in the code "main-loop" it just stops, no return, goto or even a THEN to go with the IF.

Second thing. If the only place you are trying this is on a simulator, good luck.
Use a bread board for your simulator.
- 24th December 2008, 06:27
Darrel Taylor

There's more to the code.
For some reason vBulletin saw "Reference<Voltage" as being HTML and it messed up the post. I added a space, and now it shows the whole thing.<hr>
I think Proteus is complaining about using ADCON0=%11000001.
A/D Clock mode 3 is not recommended at 20mhz, but I wouldn't call it an error.
Using ADCON0 = %10000001 might clear the problem, by selecting FOSC/32, which is what the comments say you wanted anyhow.

But I think the biggest problem is that the execution from the beginning falls into the get_reference Subroutine.
When it hits the RETURN, it has no idea where to go, because nothing GOSUB'd to it to begin with.
You should have a GOTO main_loop before that point.

You should also put some limits on CCPR1L.
It shouldn't go above PR2 (49) or try to go below 0.
Just some IF statements will fix that.

hth,
- 24th December 2008, 06:43
Archangel

Quote:

Originally Posted by madxice

Hello everybody,

I am trying to make buck converter and control it with 16f877. The logic is simple. If the output voltage of the buck is higher than reference voltage the pwm duty cycle will decrease, if the output voltage is lower than the reference the duty cycle will increase. It seems very simple, but I couldn't be able to write the program:( I write but i doesn't work. I am new at pic programming. Help me please!!!

My crystal is 20MHz.

And it gives an error " ADC conversion clock period (1e-7) is possible invalid for device clock frequency" in proteus simulation.

Code:

DEFINE OSC 20 DEFINE ADC_BITS 8 DEFINE ADC_SAMPLES 50 TRISA=%00000011 TRISB=00 TRISC=00 TRISD=00 TRISE=00 Reference var byte Voltage var byte CCP1CON=%000011100 CCP2CON=%000011100 T2CON=%00000101 'timer 2 on, 1:1 postscale, 1:4 prescale PR2= 49 CCPR1L=%00011001 get_reference: ADCON1=%00000000 ' Set LEFT Justification ' Enable ALL ADC's (using PIC16F87x as example) ADCON0=%11000001 ' Set ADC Channel 0 (RA0/AN0) ' Enable ADC Module PauseUS 50 ' 50uS Pause to allow sampling Capacitor to charge ADCON0.1=1 ' Start Conversion While ADCON0.1=1:Wend ' Wait for conversion to complete Reference=ADRESH ' Read 8-bit Result return get_voltage: ADCON0=%11001001 ' Set Fosc/32 ' Set ADC Channel 1 (RA1/AN1) ' Enable ADC Module PauseUS 50 ADCON0.1=1 While ADCON0.1=1:Wend Voltage=ADRESH return azalt: CCPR1L=CCPR1L-1 return arttir: CCPR1L=CCPR1L+1 return sabit: CCPR1L=CCPR1L return main_loop: Gosub get_Reference ' Get reference value Gosub get_voltage ' Get voltage value if Reference>Voltage then azalt if Reference< Voltage then arttir IF Reference=Voltage then sabit goto main_loop ' Do it forever end

I do not know how or if it will affect your code, but I did notice your CCP1CON and CCP2CON register settings have 9 bits.
- 1st January 2009, 10:13
madxice

pwm and SPI at the same time

Hello again,

For my buck problem, I found a good example. With little changes I applied to my circuit. Now it is working. This circuit was maintaining the voltage.It was infiinite loop.

Now, I want to use SPI module of 16f877 for TLC5941 led driver IC. It uses CLK, SDO outputs continuously. This should be infinite loop too.

May be it will be a silly question. But is there any way to use same pic for 2 different infnite loops? Do I have to use 2 pics. I can use, but if it is available I want to do it with one pic. Because I think to use rgb leds. And if I use 2 pics for one color, it will increse the total number of pics in my whole project.
- 24th May 2009, 13:11
art-666

Quote:

Originally Posted by madxice

Hello again,

For my buck problem, I found a good example. With little changes I applied to my circuit. Now it is working. This circuit was maintaining the voltage.It was infiinite loop.

How nice you found code, but why not share it so we can follow.
- 9th July 2009, 14:47
surfies

Yes I would also like to see that code