20-06-2019, 08:04 AM
Fair enough, non contact is certainly safer for the Arduino! There are a lot of bad examples of how to do it directly out there. Just remember (and I am sure you know this) when measuring off the cam it's only going half the crank speed. Also when running any wires to your remote sensors use shielded cables. It will help prevent noise upsetting the Arduino side of things. Years ago I made an optical tach using an Arduino to measure the RPM of a home made jet engine. That would go over 100 000 rpm so you shouldn't have a problem with an Austin 7 engine!
Another possible non contact way to do it (and I haven't tried this so no idea if it would work on a car) is using a neon bulb off the high tension side. I have once built a sort of simple opto isolator doing exactly that with a neon bulb and a LDR or photo transistor in a tube. The neon is on the output of a dynamo in an old wind up telephone triggering an Arduino to play old fashioned music. It works very well.
Simon
Another possible non contact way to do it (and I haven't tried this so no idea if it would work on a car) is using a neon bulb off the high tension side. I have once built a sort of simple opto isolator doing exactly that with a neon bulb and a LDR or photo transistor in a tube. The neon is on the output of a dynamo in an old wind up telephone triggering an Arduino to play old fashioned music. It works very well.
Simon