Infrared emitter and detector pair

I have an ancient tachometer (displays RPM on an analog meter ;-) that uses light from a focused flashlight bulband a relatively fast detector to measure RPM using reflected light. I use metallic duct tape (aluminum, not cloth) as the reflective surface if the shaft/fan/whatever does have sufficient contrast.

I think that same tape would work for IR.

I have a newer laser + photo-diode version for measuring speeds above

John

You can't make nothing for 40 bucks.

I'm sure you can get the IR source->mirror->photodiode to work. I'm not sure I'd want to mount it on a IC motor and expect it to stay aligned with all the vibration.

How 'bout something else... surely there's lots of ways to sense the RPM of a motor. Can you pick off a signal that does the spark timing? Maybe a coil wrapped about the spark plug wire?

George H.

Sure; you can buy an emitter/sensor pair already packaged to accomplish that (Sharp GP2S24xxx parts are the first my catalog here mentions).

But, what do you mean 'flywheel'? If this is for an automobile, there's no need to do anything exotic, the primary side of the ignition coil has a large and reliable electrical signal all ready for you.

--- If you can get Fairchild to sample you one of these:

or if you can get one through disty, you'd probably be better off than trying to cobble something together out of what you have on hand; no offense intended. :-)

There are also reflective sensors available which exhibit greater sensitivity by having their emitter and detector angled so that their axes are collinear when a reflective surface with its plane normal to their half angle is placed a certain distance away from them, but I'm off to cook roasted beets, baked chicken thighs, and sliced tomatoes sprinkled with oregano and drizzled with extra virgin olive oil for dinner, so I can't help with that search right now. :-(

;)

--- JF

How is "extra virgin" olive oil different from plain ol' ordinary everyday olive oil, other than the price?

Thanks, Rich

"Virgin" means that it's olive oil (no chemicals added). "Extra-virgin" means it's from the "first pressing" of the olives and is supposed to be better. Neither of these terms have any legal meaning and the meaning words, if not the oil, are often adulterated.

Those are similar to some Omron opto-reflective sensors I used as the pedal switching in the pipe organ I built 23 years ago. Those, some black masking tape and 3M reflector tape worked just fine. 2 sensors per pedal and I had MIDI velocity.

G=B2

--- From:

"Extra-virgin olive oil comes from virgin oil production only, contains no more than 0.8% acidity, and is judged to have a superior taste. Extra Virgin olive oil accounts for less than 10% of oil in many producing countries. It is used on salads, added at the table to soups and stews and for dipping."

--- JF

Thanks for this - I fear I've never tasted olive oil, and am kind of surprised that it has any flavor at all - when I get a salad and ask for "just some oil and vinegar on the side," what they bring, according to my taste buds, might as well be Mazola or 10W30. ;-)

Thanks! Rich

There ya go... even easier than mucking with the high voltage side.... always a worry that the HV will fry something.

George H.

No, I was thinking about sensing the current in the coil.... But better to work on the primary side as Whit3rd suggested. Too much worry about getting 'whacked' by the HV.

George H.