Pic Speed / Instruction Speed etc

[Acetronics2]

Hi, Jamie

@ first ... there is a small thing I do not understand so well ...

you count the teeth ... oK ... but the way you use rising AND falling edges make 2 transitions per tooth ... or 70 transitions per turn ...

the way the program is written - and taking 70 transitions into account ... I get a 13200 rpm counting limit @ 4 Mhz...

Alain

[Bruce]

Use a hardware counter like Timer0.

Here's one example; http://www.picbasic.co.uk/forum/showthread.php?t=10608

If you get 2 pulses per tooth just set a 1:2 prescaler for 35 counts per rev.

[jamie_s]

alain - yeah i found that out when i tested with the scope - i just doubled the numbers in the case statements and it worked fine. As the max speed is around 8500rpm, testing it seemed fine on the bench.

[Acetronics2]

Hi, Jamie

... having 3 pulses per turn and a 8500 rpm limit ... make me think of a somewhat "unusual" engine ...

could you tell me which engine it is ... may be I can be VERY interested in ...

Alain

[jamie_s]

suzuki v6, and i want to decode a crank trigger to run an aftermarket tacho.
it probably will never see 8500rpm, but i want to ensure the pic is stable at least to 7000rpm

[enauman]

I know this is an old post but I made a tach adapter using a PIC 16F1824. It basiclly takes a single cylinder engine signal (1 pulse /720 degrees) and multiplies it by 4 to use a 4 cylinder tach. Works real well if you are interested, I can send you the code. It can be adapted to other situations as well. I also designed a real stable interface to the coil if you don't have a crank trigger.