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As some of you all may remember, my dad and I are wood turners with a couple of lathes in the basement. Well my dad's been getting creative, and pretty good too, and has a need for a low power strobe that is triggered when the turning goes by a certain position. For the strobe he's planning on some high intensity LED's and was trying to figure out what to use for the trigger.

So I thought, well I've got an extra engine sitting around with a working cam and crank sensor. So we were wondering just how exactly do these guys work. Are they hall effect sensors or just proximity sensors? Does anyone have any specs on them, Vikash? My brother's an ME with a bit of controls experience and dad's EE but if someone could shed some light and save some time it'd be appreciated. Any other ideas and/or suggestions are also welcome.

Thanks.

They're variable reluctance pickups. Try Googling "variable reluctance" and then reading the FSM pages about the cam and crank sensors.

But... how fast are these lathes turning? What about just attaching a magnet to the rotating shaft and mounting a magnetic reed switch next to it?

Thanks. I'll check into that, they may not be worth the work over just getting a straight proximity sensor.

He won't need it for sanding so around 600-1200 rpm depending on what kind wood and what diameter.

do stop and consider those two sensors range from $150 to $250 to replace unless you can find them on a junkyard car.

They're a very expensive item for any project.

Hmm... actually, a crank angle sensor pickup might work with a timing light... If you cut the inductive pickup off the timing light and wire the sensor in its place, and put a little steel nub on the turning shaft, it's quite possible that the little blip induced in the sensor would trigger the timing light. If not, maybe a little magnetic nub.

Okay, thanks much. I'll pass all of this on to my dad and brother and let them think on it. We don't have a timing light but that'd be an easy way to get a circuit for this, hadn't thought of that.

Scuzzy, I wouldn't be using the ones of my car but I've got extras sitting on my old block, otherwise Dad'd be looking elsewhere .

the mini-magnet and pickup off of a bicycle computer would work for your sensor. As long as your RPM doesn't go over 1,000 they work well. When used on a skateboard wheel turning 4,000rpm, they do not.

Time for a follow up.

Dad picked up a timing light and my brother and him sat down and started playing with it. Ultimately all they did was snip the timing light pick up off and hook those wires straight to the cam sensor and viola, it worked. It freezes the wood turning perfect and worked a lot better than my dad was expecting. I've tried explaining to him that this sensor is meant to have an accurate response at anywhere between 300-6500 rpm but I don't think he quite gets it for whatever reason .

But it works great and thanks to all for the help.

Yay.