Arduino geekery?

[UnknownStuntm...]

So, I've got one on order for a project, I would like to create a rev counter, from a single cylinder engine. Anyone got any experience of such a thing?

[Syx]

I've had some experience with PIC microcontrollers (I have a clock working at home, and am attempting to build a device to measure lean angle) - not sure how similar they are to the Arduino kit. I would guess there are lots of setup examples out there though... and then it's just a matter of the code!

[UnknownStuntm...]

I suppose what I'm asking is a microelectronic pickup question really. Like, a coil of wire wrapped around the HT lead, then through some electrickery to remove spikes etc, before it can be safely fed to an I/O.

I remember years back I had some books about this kinda thing where I was supposed to be paying attention in class. Maybe I'll dig them out of the loft.

[Syx]

I seem to remember that some rev counters work by wrapping a "sensor wire" around the HT lead to induce a pulse - so that seems to be your option! I'd probably start out by doing that and passing it through a couple of filters then seeing what kind of pulse you get from it.

Edit: The filters you need will most likely be the same kind you get on voltage transformers, as they do the same thing (smooth out the "spikes"). Although I would guess you don't want to oversmooth as it is the spikes you'll be using!
Here's a similar project that includes a schematic: https://www.quasarelectronics.com/smart-kit/1143-digital-rpm-indicator.htm

[The Shaggy D.A.]

I'd be tempted to try a 555 timer as a Schmitt trigger with, as Syx has mentioned, a few loops of wire wrapped around the HT lead. The 555 will then produce a clean (reversed) square wave which you should be able to count on the Arduino.

https://www.kpsec.freeuk.com/555timer.htm#buffer

I read that if you don't have access to a test signal generator to calibrate it, you can always use the 50Hz from mains hum, which would be 3000RPM
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[UnknownStuntm...]

Excellent, I shall break the soldering iron out as soon as the ard turns up, you two are suitably rewarded for some inventive thinking.

Need to get 6 engines' rpms simultaneously, (well, maybe two engines, as they'll be arranged in two banks of three) and prepare some way of showing the data. It's for a power tool drag racing project you see...

[Syx]

Such is the complexity of life - a simple description hides a much more involved project!
Best of luck with it

[G]

My Veypor and the aftermarket tacho on the SV650 race bike I did have both cut into the +ve to the coil (before not after).
Using one of those splicing style connectors.

[UnknownStuntm...]

Well, the engines have no way to get a LT signal out. It's a two stroke disc cutter, and they have a sealed ignition amplifier with a massive magnet to generate the spark. I think the only way I'd be able to pick up the signal would be to wrap a wire around the HT lead.

But anyway, something dawned on me yesterday, it's a single speed thing, so I can just use a bike computer sensor to get the speed of any of the wheels, it'll be directly linked to the rpm of all the motors...

[Syx]

Being single speed does make things much easier... although I'm not sure if the accuracy of a bike speedo is much to shout about!

[UnknownStuntm...]

just the sensor I'll be using, driving the arduino. It needs to manage the second stage of events you see.