I scavenged a microphone plug from a broken headset, soldered a couple of inches of sturdier wire to minimize working with its flimsy wires, soldered 2 diodes across the ends of those wires (in opposite polarities: this shorts out voltage over .5), then a 10K resistor in series, ran this around the ignition coil wire of my pickup (1 loop), recorded (with sox's rec) a few minutes of the engine idling. Then I analyzed it with Audacity. I'd recommend a higher resistance, but I don't seem to have broken anything.

That's really cool that you were able to do that.-

What device did you have Audacity installed to?

may we hear that recording?

sounds like something a german industrial band could've made in the eighties?

I ran Audacity on my computer. I wanted to run an oscilloscope program so I could look at it real-time, but I couldn't get xoscope to work - so I recorded a few minutes with sox's rec then analyzed the output with Audacity.

LQ's rules allow only pictures and text attachments. As consolation here's 2 seconds of Audacity's display.

Listening to the recording, the speed-up of the idle is much more noticeable than it is when I'm driving it.

I failed my last emissions test because the idle was too high (the emissions were okay). That's why I'm doing this. I lost my tachometer in a theft a few years ago and resented having to buy another.

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I don't have a soldering iron but thinking about getting one.

Is soldering a simple task? Not safe to breath in?

I picked up a cheap Bluetooth ODB2 dongle on Amazon (<$20) and use it with TorquePro on my Android devices. Depending on the vehicle you'd be amazed at the amount of data that's available from one of these things

Yes, but you need to learn and practice a bit to do it well. No. It (flux fumes) can be an irritant and could be a problem if you have asthma or other breathing problems. Soldering occasionally should not pose a big health risk.

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you should.
it's cheap and fairly easy and you can make really good electrical connections or repair the odd loose contact, things that could get really expensive otherwise.

the fumes, well don't breath'em directly for hours, i guess it's just like exhaust fumes or something.

one caveat:
as electronics have very small soldering connections and are getting smaller all the time, there's a limit to what you can do even with a very small soldering iron and a very steady hand.
the last time i repaired a mobile phone with a soldering iron must have been in 1999 or so.

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Thanks!-

I will look for a soldering iron online. Thanks.

I'd like to build a small robot one that avoids objects.

RandomTroll,

Your idea was incredibly unique and genius.

Thanks for sharing:-

Good idea RT.

Z &c:
Etching basic circuit boards is pretty easy too, you should find kits or tutorials on both.

Here's a great open source book on the subject: https://www.ibiblio.org/kuphaldt/electricCircuits/

Reminds me of electronic stores* where they mark up (e.g.) the cables hundreds and hundreds of percents because they can't get their profit margins on higher end stuff: that we can't always make!

So you wrap the "probe" around the ignition wire like a clamp ammeter while it's plugged into a microphone input? Very cool idea.

You ought to write that up (include photos, etc.) and post it on a web site.