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Need some help with circuit

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Disruptor565

New Member
Hi

First of im still a noob when it comes to electronics the only time i can build something is when i have the diagram and components , i dont have a idea how to build something from scatch :eek:.

We did a conversion on a car and changed the motor form a 4 cyl 2.0l to a 2.5 v6 now my rev counter is over reading . the response i got on the other forum was this , but no one seems to know how to do it . all i know is that the rev counter is digital and the signal doesnt come from the coilpack , at idle its 25Hz and above 2500 rpm its 125Hz . so before the conversion the car would sit at 3500 rpm in 5th gear at 120km/h now its just over 5500 rpm at the same speed .

"Lol.....its bound to be wrong, you had a 4 pot giving 2 pulses per revolution and now you have a V6 giving 3 pulses per revolution.

The rev counter will be for a 4 pot so you should get about a 50% over read!

An option might be to knock up a circuit to modify the signal by dividing by 1.5. "

I hope i can get some info here on how to do this .

Thank You
 

Triode

Active Member
There are diagrams out there that show you how to use flip flops to divide signals, heres one to divide by 1.5, and the parts should cost just a few bucks. There are other options if you google "flip flop divide frequency" you'll find lots of them. But I'm pretty new at this too so I'm not sure that all you need is a pulse at a different speed. This might get you going in a usefull direction though.
 

Sceadwian

Banned
Judging by the input/output of that clock signal it doesn't just divide by 1.5 it drastically changes the duty cycle. More complex digital IC's need very close to a 50% duty cycle so be aware of that if you use it.
 

Triode

Active Member
I was thinking that, but is there any way to make a system that would intelligently alter it and keep the duty cycle the same that isn't way more complicated? Besides, doesn't a flip flop reciving a regular frequency always put out a 50% duty cycle? as in "Blip (on) Blip (off) repeat..."

nvm, I see what you mean, I think what I said would apply for halfing the frequency with a single flip flop. This seems to keep the pulse width the same but space it out. still with how much simpler it would be it could be worth a shot before going to more sophisticated methods.
 
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Sceadwian

Banned
They're called PLL chips =) Get one, they're not excessively complex.
 
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crutschow

Well-Known Member
Most Helpful Member
They're called PLL chips =) Get one, they're not excessively complex.
It can be difficult to get a PLL chip to work over a wide range of frequencies as you have here.
 

crutschow

Well-Known Member
Most Helpful Member
The duty cycle may not be that critical. Does the original signal have a 50% duty-cycle?
 

jal04

New Member
help plz abut circuit

i have bought a wireless fm transmitter from Proporta.com.
i need its circuit diagram .
where can i find it????
 

Mickster

Well-Known Member
Most Helpful Member
i have bought a wireless fm transmitter from Proporta.com.
i need its circuit diagram .
where can i find it????
Certainly NOT in this thread, since it has absolutely no relevance to the current problem at hand!!

Make your OWN post and be patient for any replies.

Hijacking other people's threads is one of the first ways to get on people's nerves around here, or any other forum for that matter.
 

Disruptor565

New Member
hi

think i finaly got some handy info , i have been told to change the crystal in the rev counter to a 5.0688mhz one i think the one it has now is a 4.1?? mhz . i will keep you guys updated.

Thank You for all the help and info
 
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