Low frequency generator

[lerameur]

Mainly I need a frequency output from 10Hz to 1200Hz approximately.
I decrease the internal oscillator down to 1Mhz and I'm getting down to 62Hz with HPWM, but the max frequency is then barely 400Hz !.
I programmed PWM myself , but with same result as HPWM.
Thought I found it with this program: http://melabs.com/samples/PBP-mixed/hardpwm.htm
Unfortunately not, played around with PR2 and other parameters, still nt getting the result I want...

K

[HenrikOlsson]

Which chip are you currently using? Can you switch to another if a more suitable solution exists?

/Henrik.

[lerameur]

I am using 16F88, at this point I am able to view all options...

ken

[lerameur]

some people mentioned by other post to play around with capture mode CCP OSC, But the bandwidth is very small, Altering with parameters changes another.. ending up where I started !!
K

[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