Simple Rev counter

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manny
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Simple Rev counter

Post by manny » Mon Mar 23, 2020 2:21 pm

Good day all,

as there about 4 people in the office and 30 working from home...your mind starts to wander....

does the negative post on a ballasted coil switch between 0v and its normal operating voltage of say 9v. ..could this power signal then be reduced by a simple voltage divider to feed the input pins of an Arduino to drive some LEDS on output pins? with some coding to decipher the input pulses?

Ta

Manny



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Simple Rev counter

Post by philhoward » Mon Mar 23, 2020 2:37 pm

9 or 10 volts up to 12 or so - assuming a ballast system. Probably best to use an Opto?

I think Andy made it a frequency input?


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Simple Rev counter

Post by manny » Mon Mar 23, 2020 2:43 pm

philhoward wrote:
Mon Mar 23, 2020 2:37 pm
9 or 10 volts up to 12 or so - assuming a ballast system. Probably best to use an Opto?

I think Andy made it a frequency input?
cool...as long as the input signal is conditioned not to close to the input pin max voltage and current...Opto sounds safer.
This 'idea' was due to my Tr7 tacho only able to register 2.5K before it drops to zero...yet to bench test it though..

Ta

Manny
EDIT- i'll pester Andy in a bit :D



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Simple Rev counter

Post by Old and Slow » Mon Mar 23, 2020 8:08 pm

Simplest might be a few turns of wire around the HT lead - produces a spike every time a spark plug fires. Worth trying anyway - simples - no cost approach for experimenting.


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Post by manny » Mon Mar 23, 2020 8:26 pm

Old and Slow wrote:
Mon Mar 23, 2020 8:08 pm
Simplest might be a few turns of wire around the HT lead - produces a spike every time a spark plug fires. Worth trying anyway - simples - no cost approach for experimenting.
That would be interesting to monitor...but the number of turns and wire gauge needed to get a suitable voltage will be good test of patience...



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Post by Old and Slow » Mon Mar 23, 2020 9:01 pm

When I did this (back in the 70's on a Mini) I used about 8 turns, wire gauge not relevant, but I used 7-strand fine wire I think.
Don't think I've still got the home-made rev counter though.


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Post by willholderogri » Mon Mar 23, 2020 10:17 pm

That's how my lpg system works the coil of wire round the HT lead activates the gas controller .


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Post by manny » Tue Mar 24, 2020 6:04 am

willholderogri wrote:
Mon Mar 23, 2020 10:17 pm
That's how my lpg system works the coil of wire round the HT lead activates the gas controller .
What voltage does the coil produce to activate the controller?...i am getting more intrigued by each post here...



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Post by philhoward » Tue Mar 24, 2020 8:26 am

It's not voltage per se - you get a (very low - probably microAmps) induced current which based on a very high impedance input gives sufficient voltage to produce the trigger signal. You can upset modern electronics by touching conducting components and your skin is pretty high impedance at low voltages (5 or 12v).

I've got a Vapor Trailtech standalone speedo/tacho unit that worked pretty well with 3 turns of wire around a HT lead on the Omega engine.


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Post by peter freeman » Tue Mar 24, 2020 9:31 am

Why try to re-invent the wheel, there are plenty of cheap rev counter out there - unless you are completely bored.



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Post by manny » Tue Mar 24, 2020 10:21 am

philhoward wrote:
Tue Mar 24, 2020 8:26 am
It's not voltage per se - you get a (very low - probably microAmps) induced current which based on a very high impedance input gives sufficient voltage to produce the trigger signal. You can upset modern electronics by touching conducting components and your skin is pretty high impedance at low voltages (5 or 12v).

I've got a Vapor Trailtech standalone speedo/tacho unit that worked pretty well with 3 turns of wire around a HT lead on the Omega engine.
surely you cant get current without voltage.. :?



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Post by manny » Tue Mar 24, 2020 10:23 am

peter freeman wrote:
Tue Mar 24, 2020 9:31 am
Why try to re-invent the wheel, there are plenty of cheap rev counter out there - unless you are completely bored.
i had one of these programmable Ardunio boards for ages...i really need to use it... so curiosity and all that..



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Post by philhoward » Tue Mar 24, 2020 10:58 am

manny wrote:
Tue Mar 24, 2020 10:21 am
philhoward wrote:
Tue Mar 24, 2020 8:26 am
It's not voltage per se - you get a (very low - probably microAmps) induced current which based on a very high impedance input gives sufficient voltage to produce the trigger signal. You can upset modern electronics by touching conducting components and your skin is pretty high impedance at low voltages (5 or 12v).

I've got a Vapor Trailtech standalone speedo/tacho unit that worked pretty well with 3 turns of wire around a HT lead on the Omega engine.
surely you cant get current without voltage.. :?
All comes back to energy. You can try and induce up to a certain voltage but if it's only in the order of microjoules, it can only generate a very small current, unless into a very high impedance/resistance. Open circuit voltage and all that jazz.


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Post by willholderogri » Tue Mar 24, 2020 1:13 pm

As said above induced pulse triggers the lpg controller


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Post by Old and Slow » Tue Mar 24, 2020 5:50 pm

A transformer actually works on current flowing in primary coil, to create a magnetic field which then induces current in the secondary. Of course you need volts to push the current flowing through the coil.
This proposed set-up comprises a single-turn coil (the HT lead) and a secondary comprising a few turns; the number of turns isn't critical. You can't draw much current out of the secondary (microamps probably) but on a 'scope you'll see a spike of about 15v, regardless of the number of turns (in my experience ! (if I remember correctly))


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