I changed my name to I started making a video on laser tacometers but I found it impossible to get an accurate reading because I couldn't stop eating the tacos.

Afrotechmods Hehehe. But seriously though, great tutorial.

A phototransistor/photodiode would indeed be the logical choice. But I didn't have one lying around and I thought it would be more fun to show people the LED trick. In the video I was referring to CdS photoresistors being slow.

+Afrotechmods that was good video. I have photoresistors and infrared sensors and Emmitors, but didn't have idea about this trick.:) Thanks

+Afrotechmods The solution here, is to Mount the led on the nose and the laser pointer module on the chin. I would call it: "Lazy" Tacometer.

Nice, that's a great solution

Jordan O'C I think your solution for this instance is easier. So I wouldn't cuss about it.

***** I am everywhere.

Jordan O'C If it's a Trex-style helicopter (with a shaft or belt to spin the tail rotor) then you can calculate the RPM from the main rotor RPM, I think mine was 7-to-1 tail/main last I checked.

DFX2KX My heli has a 6:1 ratio between the tail and the main rotor I think, but I didn't know the rpm of the main rotor either.

Simple and interesting

Look for Saleae clones, that are cheap "Oscilloscopes" for around $10

MattsInTheBelfry Sorry this was poor camerawork on my part. What is happening there is the laser is shining through the fan blades, then hitting the LED. The LED gets lit up very brightly, and since the fan's label is reflective it acts as a mirror and shows the camera the shiny LED. I am not measuring the reflection of the label, but I can see how it looked like that in the video.

+Austin Hively Photovoltaic

Austin Hively pots the same way a solar panel works....you can actually builds an adhoc solar cell from LEDs

Razor2048 Yup that would work. But you'd want to have a transistor amplifier circuit between the Fgen and the laser.

Maybe matching colors would generate the maximum voltage. Trying this with an RGB LED would be interesting

That would depend on the frequency and the sampling rate of the DMM, my Fluke 87V is able to register them, for this i use the Hi Res function...

Ferreira A . Use an LDR and a Laser.

Anvilshock sorry I didn't here what alfro said. forgive your land your landlorship. but can you tell me the time alfro saidnit.

SkaterK3 Well, I cant speak on the actual emitter, but I can say that since the plastic shell around the LED was red, red light passes through it better than any other color light, so a red LED combo's with the red laser would immediately be better for that reason.

Kakunapod Okay that's what I thought. I am wondering if a Blue LED (with a higher forward voltage) will produce a stronger response than a red LED. I think this is worth a try but I imagine that there is a small cost offset considering how expensive blue laser diodes are compared to red ones.

***** nope still confused dot com

With thick enough spokes I think it might yes

5mW should be plenty. Try different red LEDs? Green is unlikely to work well. Also try the 10x attenuation scope probe setting.

Thanks !! I'll try that !!! {:>)

Laser tachometer...

It can be a good alternative, cheap and portable

If you are serious about those questions I suggest you go back and play with wooden toys.

MrOperettalover I just wonder as I don't know, very sorry for being so uninformed! If you are still serious with your reply, I suggest you go back to the shithole you came from and be nice when you come back! Geeez...

Kenny Constanzo I never understood nice. My goal in life is to collect enemies - preferably stupid ones like you. I suggest you limit your questions to the level you're on.

I pity you, goodbye.

Kenny Constanzo Funny how they who need it the most are the first to feeling sorry for others.

+Rajat Tarade You could take the signal from the LED, amplify it to produce a 3-5V signal, and then hook it up to a digital input port on an Arduino or similar. Just count the pulses. You could also use an ADC port, but the digital port would allow higher frequency measurement. Use a transistor or op-amp for the amplifier.

The soundcard on your computer. Only AC-coupled. Don't exceed the maximum input voltage, at least not without current limiting.

+Ryan Thornburg Hz is the number of times something happens per second. RPM is rotations per minute. Since there are 60 seconds in each minute you multiply by 60.

Afrotechmods alright, i guess i can see that. thanks for the clarification

Kieran Hammond Nope.

Kieran Hammond Glebs has the answer. What you WOULD get, though, is different periods of open circuit time vs. closed circuit time, as the shape of the fan blades differs at different locations... but the number of cycles (open - closed) remains the same.

eliobou Was it a red LED? Was the probe X10?

Afrotechmods I tried a classic red LED and a superbright red LED and the probe is X10

+Josh Savage Its only because I don't really want to spend a lot on encoded motors..

You can get some logic gates (probably 74xx series ICs) and do binary calculations. Add a converter from BCD to 7 segment display and you have whole device. Only thing I'm not sure how to do is the actual measuring of the frequency of the pulses.

+Flankymanga In a lazy explanation I could refer to a "Faraday principle", when you build a motor you can use it as a generator, when you build a speaker you can use it as a microphone, etc. As I understand, when an LED (read a semiconductor junction) is crossed by electrons, these electrons must quantum leap to switch material. Because they fall in orbital, the atoms emit light (as any atom where electrons leap around for some reason). When any kind of material receives photons of proper frequency, the electrons will leap so that the atom absorbs the photon. On a LED, the absorption of the photon forces electrons to skip across the semiconductor types and so this generates a voltage (as in photo-electric effect). That's the quantum physics explanation for you.

+Flankymanga just look for photoelectric effect. Einstein got his nobelprice for this