HPWM at very low frequency

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- 23rd December 2010, 01:49
lerameur

HPWM at very low frequency

Hi,
The very short program works but the frequency output is extremely variable from 500Hz to 2Khz. The program should max at 512Hz..
Also the output is very noisy, any recommendation on the output ? extra capacitor ?

Code:

'////////////////////////////////////////////////////////////////////////////////// '// 555 simulator using PIC16F88 '// Variable frequency, fixed Dutycycle '////////////////////////////////////////////////////////////////////////////////// '///////////////////////// '// Define section // '///////////////////////// INCLUDE "modedefs.bas" OSCCON = %01110000 '8 Mhz DEFINE OSC 8 ANSEL = 0 CMCON = 7 DEFINE CCP1_REG PORTB 'Define output port of pulses out DEFINE CCP1_BIT 0 'Define output port of pulses out Define ADC_BITS 10 ' Set number of bits in result Define ADC_CLOCK 3 ' Set clock source (3=rc) Define ADC_SAMPLEUS 50 ' Set sampling time in uSec TRISA = %11111111 ' Set PORTA to all input TRISB = %00000000 ' Set PORTB to all output voltage_check var word Frequency var word Mainloop: ADCON0.2 = 1 'Start Conversion max 1024 ADCIN 3, voltage_check 'analog pin 1 get the 10 bit result Check the battery voltage on pin PORTA.3 Frequency = voltage_check /2 'max 512Hz HPWM 1,126,Frequency goto Mainloop END
- 23rd December 2010, 09:02
mackrackit

This has the ADC turned off.
ANSEL = 0
Try
ANSEL = %00001000
- 23rd December 2010, 09:13
Acetronics2

Hi, Dave

did you notice the generator will only output 489 to 512 Hz ???

... RTFM ??? :D

Yes Ken, you should read your manual, HPWM section ( or the Pic Datasheet ! )

Alain
- 23rd December 2010, 09:24
mackrackit

Quote:

did you notice the generator will only output 489 to 512 Hz ???

Yup, and the OP said it was going from 500 to... So that part sounds about right. Does he want something slower?
- 23rd December 2010, 12:24
lerameur

Argrr, ya, I read the text but I skipped the table, But I need lower frequency then 489Hz, Actually I need between 10 to 300Hz, I think I am better off with what I am using now, a 555 timer.

K
- 23rd December 2010, 12:41
Acetronics2

Quote:

Originally Posted by lerameur

Argrr, ya, I read the text but I skipped the table, But I need lower frequency then 489Hz, Actually I need between 10 to 300Hz, I think I am better off with what I am using now, a 555 timer.

K

you can use a PIC, but with " soft " PWM generation ... :rolleyes:

Also have a look to what the CCP module can do for you ... more than generating PWM.

in Compare mode, for example ... you easily can reach 2Hz ...;)

a Timer1 Overflow interrupt also will work fine ...

Alain
- 9th May 2013, 08:41
lerameur

Re: HPWM at very low frequency

HI,
I read page 83 concerning compare mode... still have no idea how you could get 2hz .
The manual says even in PWM mode we cant get lower then 5ms long witch is about 200hz...

K