How to build a simple laser tachometer 

With the right LEDs, you can use the one LED to power another LED. I had a setup while I was interning at NASA where one super bright red LED was shining on another one of the same LEDs, and that LED was connected directly to a 3rd red LED, powering it! I measured around 2V or so on my meter without load! It was very dim, you could just barely see the die glowing, but enough to be an impressive proof-of-concept. (I was measuring the slew rate of the LED as a sensor compared to other 'real' sensors.)

At first i thought it said "laser tacometer" I was excited to finally measure the amount of tacos I had.

Great, useful and crisp tutorial. Thanks!

Lovely work Afro. Can you do a video about comparators and how to use them to make a short circuit protection circuit??

awesome idea, had to try it out. first important discovery is, that when working with red laser, it works only with red diode. I'll try it with green laser and diode, once I find the green laser pointer.

I've got another one for this! This morning, I wanted to know how fast a motor, which was not connected to anything, so had no fan blade or anything for a tachometer to work on, was spinning. I put a small neodymium magnet on the side of the output shaft and simply held my oscilloscope probe next to it. as it spun, it induced a very measurable voltage in the probe.

Great videos! Looking forward to seeing more.

I just though by hooking up the same thing to an arduino and using it to measure the minute changes in current and using an 8 bit display and output the RPM and just to complicate the project use an input mode for arduino and get the number of blades and use that to process too.

Very cool! Thanks for the tip!

Awesome Vid....might have to break this out in class to impress my electronics instructor. it will more that likely stump him at first! lol.

An application im building needs me to measure the rpm and this is a great input to it. However, I do have a query. If the surfaces of the emitter or receiver is subjected to a dusty or mucky environmental conditions, I highly doubt the readings will be accurate or will emit any reading considering they are sort of blind folded. Any advice or other methods to overcome this?

Using this method i found out how to build on of those laser alarm things ypu see in movies using a signal amplifier and an arduino

Again another great videos thanks a lot!

be cool to have more videos like these.

If you use it outside, does the sun interfere with the signal?

Just so you know: This effect is described in one of Forrest Mims' books.

Whats the effect called? I want to know how the laser produces an electric current through the LED

wow this is fantastic! thanks for sharing :)

+Afrotechmods svaka ti cast teslin si naslednik vidi se da si srbin i hvala ti sto ima prevod

Hi, I m a noob and recently got into arduino , so if i will need a osciloscope to make this ? is there an alternative ?

Good one I like it

Didn't know that, thanks :)

Can you make a tachometer with arduino for 6 cylinder engine using this setup?

So this is a photodiode, right?

Will a multimeter measure the frequemcy of half rectified sine waves?

Afrotechmods What is the reason for using a red LED for this? Is just what you had laying around or was it most compatible with the laser diode that you had?

you're the beest hhh wow

Any easy explanation what physics is behind this?

WIRELESS POWER TRANSFER VIA LASERS!!!!!!!!!!!!!!!! haha

i want to build a speed tester what would i need as i need to know the MPH

KEWL!

How is the "real" tachometer you use in the end built? What kind of sensor picks up the speed, and does the laser itself have anything with the measurement to do, or is just a "pointer"? I´d like to build something like that to take control measurements of flywheel RPM on my boats engine so I can input the right dividing factor in the engine tach...

It's not the volts that kills you, it's the murderer.

CAN YOU USE A DIGITAL MULTIMETER WITH HZ READING??

Afrotechmods maybe i can get some tips on my multimeter, i think im following you corrrectly tho im not getting any results, here i have i5.walmartimages.com/dfw/dce07b8c-af65/k2-_9d4c0362-9e07-4569-b98c-1cef69142a20.v1.jpg and i have all sorts of LED's as well as that same type of laser pointer. as far as my multimeter i have the red plug on DC10A "far left port" and the black plug in the middle COM port and the dial i have it set to DC mA which is the 1st CW blue box according to this link i5.walmartimages.com/dfw/dce07b8c-af65/k2-_9d4c0362-9e07-4569-b98c-1cef69142a20.v1.jpg i did also tried the yellow box next to that DC mA and either gave me a reading thanks in advance some question that might simplify my understanding of your results might be * does it matter how much current or voltage your supplying the laser diode? * does it matter what polarity you have the led hooked to the multimeter? " anode to + , cathode to - vise versa on the multimeter? " * does it matter the color of the led? side note i am looking to implement this type of design using some sort of pcb /breakout board setup which can read this value as your video and have that read wire plugged to my arduino so i can run IF statements in the IF void loop section this is for my robotic design i am currently using a magnetic hall sensor which requires a magnet and a ic hall sensor and i think this setup you have here will be much better weight wise as both of your items weights less than my current setup..........as always thanks for your videos!

God damn it... I wish this was released like 2 weeks earlier. I was curious how fast the tail blade on my 6h RC helicopter was rotating, and I didn't have a tachometer. My next best thing? Get a microphone, record the audio right next to the blade, put it in audacity, get the time between 2 peaks and convert it into RPM (then divide by the number of blades on the rotor) xD

Actually, you can hook up the LED to a headphone jack, and measure the frequency using an spectrum analyzer app or your phone. And since it's only 1.5V, it can't fry your phone! So whenever the LED is illuminated by the laser, it makes a "high" signal or it makes a "low" signal on the "microphone" input And then you just divide the frequency by the number of blades, and multiply it by 60. You can make an app that can measure the RPM for you, just enter the interruptions/1 rotation, and voila, you now know the RPM! :)

so youre telling me i need just a nitrogen spark generator and a simple LED for makeshift home security?? It was that easy all along?

Another great video as always. I just wish I had a scope now. Thanks! ps - Any chance you could make a video on how to read schematics? I understand basic circuits but I get confused when multiple components are connected together. A 555 timer circuit for example, I don't know what goes where.

I love these tutorials. Ever since I was a kid, electronics have interested me. Much has changed over the past 55 years. While I don't build or do most of the stuff in these videos, I learn at least one thing from each. Great job.

Good tutorial. what about laser to measure distant ?

Good tutorial. what about laser to measure distant ?

Very cool. 👍

The video shows the laser shining on the fan's label. Does this work at all for a straight reading? A strobe tachometer works by reflection - not by the binary breaking of a beam - so it would work on continuous surfaces. I would love to be able to point my tachometer at any rotating object and get a reading.

Fucking great job 👍👍👍👍 I love your videos.... thats the way how an practical engeneer like you explain things in a useful way.... 🙏🙏🙏 Perfect ... it seems like Great Scot looks up to your channel or the other way 😁😁 Greets from Austria in Europe

Very good. Looking forward to your next video. Thank you.

Very Cool!

Is data logging possible on PC using this design? I need to count the number of rotations as well as changes in the RPM with respect to time. Also, Is it possible to measure the RPM when keeping the laser source and sensor in the same direction (by reflection) as done by the available non-contact tachometer?. Please suggest

I am so glad you are back! Your channel went dark for a while. As a fourth year EE student, I enjoy your videos!

(anyone) at 0:23 the laser wires appear to have some shrink tubing around them, is that right? I'm have a similar laser which works fine but the wire is so thin I'm not sure how to hook it up for long term use. Just using some quick wire spring connectors for now. Any advice from the channel moderator or anyone one the boards is appreciated

could you used any laser with any led or does it have to be red led and red laser beam ? thanks

Awesome! Thanks for the explanation, very useful.

Is there a way to figure out the max response rate of an LED? e.g., have a function generator control a laser and then see at which point the LED is no longer able to differentiate between the pulses?

This is just a counter...then we have to do the calculation. It is the calculation which is the tachometer part. Is there a way to do this without an arduino? all tutorials her that I can find use the arduino.

I wonder whether there is any disturbance when working in bright light environment.

Thanks a lot my friend for this video .

Awesome! Thanks for sharing

Believe thatd be called a frequency meter, not a tacho meter..

Hi you share a arduino laser code and shematic for a rpm dc motor ?

I'd like to use this trick to make an oscillator where the rpm of the motor determains the pitch of the (square wave) note. Would this be possible (ofcourse it is). Would it be worth it?

Great video as always, thank you!

I missed your videos!

In case of propeller rmp measurement on an airmodel, where can I place the laser? The sensor LED could be placed at the fuselage. Sorry for my bad english, I'm brazilian. Thanks.

Good video, I performed a lot of these tests back in the late 1970's but LED technology back then is nothing compared to LED's today. Most of the LED's I used back then were low intensity for indicators. Thanks .........

straight to the point video thanks for sharing.

A nice experiment ! I wonder if you can use two same LEDs instead of using a laser for simplicity. Could you even make a solid state relay using this with some sensitive MOSFET ?

this didnt work for me. what did i wrong? I conected my Oscilloscope to the LED -to- +to+ and nothing showed up. Also a Question: Can this setup be used to transmit serial data?

That's so neat ! Thanks for the tip :)

I wonder what the physical mechanism is by which the LED is coupled to illuminated object. I would expect such coupling and its electric effects to diminish with distance.

does the voltage depend on the laser color? I wonder we'd get the same reading if a green laser was used on a red LED. I feel that we'd get a maximum reading for laser-LED systems that have approximately the same wavelength.

you are showing us how to measure rpm with a 11000euro oscilloscope? that's just mean!

Interesting inddeed. Bu what type of lazer is used in this experiment, if I may ask?

what about the distance between each blade?

Well, you know, you can always use a solar panel

Could you please make a video showing how to make an FM or AM radio? I know videos like this already exist but I would like to see your take on it.

Brilliant! Thank you!

does it have to be a laser pointer? (ie: would it also work with an IR transmitter?)

do we need to connect the led with battery? any LED work? can I us the battery lezar?

you would get much better results using a britght white led a sensor

Would love to find an Arduino version of this...cuz I just can't find a free o-scope laying around n I'm not buying one for the level of tinkering I do

Awesome!

You are a wealth of knowledge. Love your videos !! Please keep doing this for another 200 years.

angreji

ooh i need siliscope, how about multimetter with out hertz reading

How difficult would it be to build a small circuit to be able to use it without an oscilloscope?

Thanks a lot i am engineer but i had no hell idea before that led can be used in that way..

Excellent video, thanks for sharing....

I hooked up an led straight on my oscilloscope and got a laser point at it but the voltage only change in a range of 5mV. What is my mistake ?

I think it could be used for alarm system

could you have two led linked shine lazer at one and the other lights up?

I really like this video. for a diy cnc encoder sensor perhaps.

14 Amish people mysteriously found RU-vid

So would this work on a bicycle wheel with the spokes?

can i use a simple multimeter instead of using a oscilloscope?

But i guess having an oscilloscope to read rpm beats the purpose of cost and portability.are there any alternatives for an oscilloscope

I can't wait to try this! Awesome vid!

I tried this with a green laser and a blue LED, and I saw no current with my multimeter. Do I need an led and laser of the same color?

+Austin Hively its called the photo electric effect

am gonna trai it

As always an other great video. Tnx for sharing