I'm trying to make an engine analizer.
To find TDC I want to use a reflective piece of foil on the flywheel.
Sooo I opened up my laser tach to see what they used to detect the RPMs.
Inside I found what looks like a photodiode.
Looks just like this:
except it only has 2 leads.
It puts out red light, looks kinda like laser light but isn't columnated, a lens is used to focus it.
Half tempted to just use the laser tach as the sensor.
The damn photo diode costs way more than the laser tach, ha.
A tachometer would typically use a photodiode or phototransistor to detect the reflected light. The output light would would be an LED or laser diode.
Yeah, the laser diode isn't actually the sensor so this might be the wrong forum but I'm wondering if anyone knows where to get a cheaper laser diode that has only 2 leads?
Hard to believe the price on that little laser diode I linked to is $459. A little more than I wanted to spend.
I think the detector is a photodiode that looks like an LED. Those are cheap enough and faster than a phototransistor.
To proccess the signal from it, it looks like they ran it through a dual op amp, then a hex buffer before running it to pin 12, INT 0 of an atmel chip.
175mW ?!?
That's er, why the diode is so expensive. Well, that and the colour. It's more or less the same colour used in blu-ray gear.
Not only, but it presents a serious risk to permanent eyesight damage.
If you weren't aware already, you can do this sort of thing with a 1mw red laser.
Now those are a different proposition when it comes time to visit the register. I bought a keyes module from DX or Ebay
for the princely sum of $2.60
I intend to use it to make a tacho for a R/C plane propellers. It also makes a mighty mean remote-control extender... :evil-grin:
Oh, I didn't pay attention to the wattage, it looks just like the one in the tach but has 2 leads,.. I'll see what other products they make in the same package.
Something in the 1mw range, ha.
Know of any writeups on how to build a digital tach using these or at least provide a digital signal/trigger to an arduino?
If the one you are talking about works with remotes it is probably invisible right? Infrared?
Got a matching photodiode in mind?
I figured they weren't something you were familiar with and had simply overlooked the Pmax figure.
Not off hand, but there's a bunch of them floating around. Basically, you just trigger an interrupt when the signal from the detector goes high or low. You keep a running count of the number of times it happens in a set period, divide by the number of items that block the light, then multiply by (1min/time-period).
As for the colour of mine. Nah, it's as red as red as red as can be. I've used both (a) a diode salvaged from a $2 led torch/laser combo and (b) a Keyes 'for arduino' module I bought from DX.com for about $2.60
As for the detector, you can buy one on it's own, or do as I did, and salvage one from an old piece of equipment. I just yanked the detector out of a photo-interrupter. It's often used in cdroms, dvdroms, printers, scanners etc. For reference, both elements inside the interrupter appear similar. The discerning factor being a red dab of paint on the detector.
Apparently, you can also use leds as a fairly weak detector. Some colours are better than others, I forget which.
Ahhh! Just found an old post I made on the subject, complete with a pic of an opto-interrupter. Hope it helps.
Yes this has helped me on my way.
I have some of those interupter counters from the printers I take apart,.. but I didn't know they could be taken apart.
Next question is how far from a photo-diode sensor should I put the arduino?
I want to have it displayed on a screen inside the car while driving so should I make the run from sensor to arduino short, and what kind of cable.
or should I make the run from the arduino to laptop short.