My brother installed a 8 cylinder engine into a car that used to have a 4 cylinder. Now of course the tachometer is reading 2x the correct RPM. The original car tach reads pulses from the distributor and he would like to use the original tach with is new engine. Is there a way to do this with logic chips or a analog circuit to divide the signal by 2?

Thanks,

Mike

 

if it uses a counter u would need a flipflop that will divide the pulses applied to its clock input by 2.
(edit: maybe someone can provide a more elegant solution)

 

A single chip sounds like an elegant solution to me

(* jcl *)

 

I concur. Any old flip-flop chip capable of running on 12V and sourcing enough current for the meter circuit would work just fine.

 

Should Mike be concerned about noise due to the steep rising and falling edges of the flip flop output?

 

that shouldn't be a problem. i've not had any of my speed sensor or tach circuits cause a problem with a square wave output. i actually needed to isolate one project and used an audio transformer driven with the square wave, talk about a nasty output. but it worked fine.

 

An innocent D-Flip Flop sould complete the puzzle without any glictches.

 

i was thinking of T or jk in toggle mode.
what wud be the inputs for a D FF?

 

You tie the ^Q output to the D input. The clock will toggle so the Q output changes at half the rate of the clock.

 

got it.
thanks a lot.

 

Thank you gentlemen. I happen to have a drawer full of Flip Flops. I will try one out and let you know how it worked.

Thanks,