Low frequency generator

[HenrikOlsson]

Hi,
If you run the PIC at 1MHz and set the TMR2 prescaler to 1:16 then the lowest possible frequency, ie with PR2=255, would (if my calcs are correct) be around 24Hz, 1/(256*4*2.5us*16). If you run that thru an external flip-flop you'll get a divide by 2 ratio so you're down to 12Hz AND you'll get your 50% dutycycle for free - without having to change the dutycycle registers when you change frequency. You should be able to reach 1200Hz with this setup, ie PR2=1 the PWM frequency would be 3125Hz which, after the external 1:2 divider would give you 1562.5Hz. However, the granularity or resolution at the top end will be far from great.

What else, except generating this frequency, is the chip going to do?

/Henrik.

[Demon]

With no experience in PWM, could DT-INT clock be used for this?

Robert

[Acetronics2]

Why not easily generate 1000 - 25000 Hz ( straight with PBP ...) and use a , say, CD 4518 or 74LS390 as a 100 divider on the output ...

as duty cycle is supposed to always be 50% ... no problem then !

Alain

[mark_s]

If you can't make your pic16f88 work. The pic18f2431 with a 4mhz clock can output a pwm about 2hz using the power control pwm module. I know you said simple, but simple isn't always easy.

[lerameur]

I need to control frequency and Duty cycle (I mentioned earlier 50% Dutycycle cause I can easily get any Dutycycle the problem is frequency, but variable dutycycle is better) . I also want to output the frequency and dutycycle on a LCD.I had this thin g going out high and low pins.... but obviously LCDout played a destructive role in the timing. ...
I will check out all the possibilities and the power control pwm module with the F2431

[Demon]

Going out on a limb with this.

PIC 1 outputs signal on a pin, PIC 2 reads signal and displays on LCD, interrupt on 4 input pins on PIC 1 adjust duty and frequency. This way the LCDOUT doesn't interfere with the pwm.

Can we even read PWM signals with PICs (never even got close to doing this)?

Robert

[lerameur]

HUmm.. two pics.. well
I thought about going to a waveform chip like the ICL8038.. but I wanted a more 'modern' solution going with a single Pic,
I am going try tonight what Henrik mentioned above.

K