Introduction: Wireless L E D

Picture of Wireless L E D

This is a way  to light up an LED without connecting any wires to it.

(The music is from Rick Astley's "Never Gonna Give You Up")

 A simple transistor oscillator circuit generates radio frequency energy, and this energy is coupled to the LED's leads which are bent into a circle and soldered to form the receiving inductor.

The circuit is as simple as it can be made, and it makes for a nice demonstration - magic trick, even.

Step 1: The Circuit

Picture of The Circuit

The circuit diagram is shown. A high frequency transistor is connected to an inductor, and biased to its active region. Due to feedback inside it, it oscillates, converting a portion of energy from the battery into radio frequency energy.

The inductor is a wire formed into a circular loop. The LED's leads are formed into a matching loop and soldered to form the receiving loop. When the two loops are placed close together (but not touching) the LED lights up.

I shall explain the circuit diagram, taking each component (or its representation) from left to right.

On the extreme left is the symbol for the battery. The longer dash represents the positive tab, the "pip" if you are using AA cells. I used four AAA cells in a holder to test this circuit. The voltage is not critical, and I tested it using the output from my mobile phone charger too.

That squiggly line is a resistor. The 33K resistor will have three orange bands on it, and then a silver or gold band.

The next symbol is a capacitor. I used a 0.1 microfarad capacitor, although any capacitor in the range 100 picofarad and upwards will work.

Then comes the transistor - I first tested the circuit using a BF494 transistor - this is a high frequency low power transistor used in the front end of medium wave radios. It overheated and died when I tried to increase the brightness of the LED by increasing the voltage to 12 V - so, keep your battery voltage down to 6V if using the BF494 or equivalent transistor.

On the collector of the transistor is the induction loop - this is just a single circular loop of wire, to match the loop of wire connected to the LED.

On the emitter of the transistor is an inductor - the value of this, too, is not critical, and any value from a few tens of microhenries upwards would work. The one I used (found in my box of junk) had a value of 330 microhenries - marked by two orange bands and a brown band.

This completes the oscillator. The resistor supplies current to the base of the transistor so that it will turn on and pass current. The base is grounded for rf by the capacitor, while still allowing the base to get current.

The emitter is allowed to float at rf by the inductor, while the current returns to the battery through it.

On the receiving side, the leads of the LED are bent over to form a circle. The rf induced in it is rectified by the LED and it simultaneously emits light.

Step 2: Components

Picture of Components

Here is a list of components:

1. 6 volt battery - four AA or AAA cells in a battery box.
2. One red Light Emitting Diode (red LED)
3. One transistor, type BF494 or equivalent
4. One capacitor, 0.1 microfarad (disk ceramic)
5. One resistor, 33 Kilohm (33K 1/4 watt) - orange, orange, orange, (gold/silver)
6. One inductor 330 microhenries - orange, orange, brown, (gold/silver)

Wire, solder, etc. as needed.

The resistor and the inductor both look alike - this can get you confused. The inductor is likely to be larger, and will be attracted strongly by a magnet because it is a fine coil of wire on a ferrite core.

The resistor can be identified if you have a meter - it will measure the value marked on it, while the inductor will show as a very low resistor, despite being marked exactly like a resistor is of a higher value.

Step 3: Construction: LED

Picture of Construction: LED

The LED can be prepared by bending its leads around any convenient round object and soldering its ends together. If you have extracted it from somewhere and its leads are too short bend another piece of wire into a circle and solder it to the ends to make an assembly as shown here.

Step 4: Construction: Oscillator

Picture of Construction: Oscillator

Constructing the oscillator circuit is very simple: All the components are just soldered together to form a self-supporting assembly.

The transistor I mentioned in the parts list (BF494) died, and the one in the pictures is another one (one of many that I tried) that worked, that I found in my junk box.

First, the capacitor and the resistor are soldered together in parallel. Keep the leads short. They may go together any way - they are not polarised, ie, have a "positive" or "negative" terminal. When both their leads have been joined together by two blobs of solder they may be handled as a unit.

Next, identify the base lead of the transistor and solder one end of the resistor-capacitor parallel network to it. Some types of transistors have the base lead in the middle, so look up the data sheet to find out. Or you can try to identify the base by using the multimeter (if you have one, and you know how to use it).

Next, take a length of stiff wire, form it into a circle about the size of the loop on the LED and solder it between the other side of the resistor-capacitor combination and the collector of the transistor.

The inductor gets connected to the emitter, and the supply wires get connected as shown.

The only tricky bit here is identifying the three terminals of the transistor, once you have done that, the rest is a walk over.

Step 5: Operation

Picture of Operation

Connect the oscillator to the battery. The emitter of the transistor goes to the negative pole of the battery, and one end of the loop that connects to the resistor-capacitor combo goes to the positive pole.

The transistor might get slightly warm - this is normal.

The LED will light when it is placed over the loop. The maximum brightness will be observed when the two loops are most close together. The range of this simple circuit is only a few millimeters at most, but even then it might puzzle a few people.

Hide the circuit under a sheet of paper and your LED will mysteriously light up when it is placed in just the right spot! It's magic!

More importantly, building and making this simple circuit is fun, and the experience will give you the confidence and the motivation to attempt more complex and more rewarding things.

Have Fun.

Step 6: Conclusion

Picture of Conclusion

This circuit intentionally generates high frequency energy. This might potentially interfere with other sensitive devices. Use it at your own risk. Connecting a large antenna to some parts of this circuit might cause interference to communication.

This is intended to demonstrate the principles of transferring energy across a short distance without direct connection. Actual devices used for similar purposes have a more complex circuitry intended to overcome some of the limitations of this simple circuit.

I found that only red LEDs could be lit using this circuit. Red LEDs have the smallest requirement of voltage to turn on: a little more than one and a half volts. All other LEDs have much higher threshold voltage and so might not work with this circuit. So stick to red LEDs for experimenting at first, when you can successfully light a red LED you might try other colours to see if they may be made to light, as well.

Increasing the area of the loops, and the number of turns of the loop, would increase the efficiency of energy transfer. But then the oscillator circuit would need more components to work, and thus will need more work to wire up and operate. Such circuits are available on the web, just do a google search on the keywords "wireless LED".


aturner7 (author)2011-06-22

The only thing I find hard to comprehend about this circuit - is that the RF that your circuit is emitting (used to power the LED) is AC. A LED will only run on DC, so unless there is a rectifier in place I don't understand how this works.

neelandan (author)aturner72011-06-22

The L E D (Light Emitting Diode) is itself a diode. It passes current only in one direction.

It will conduct during one half cycle of the induced rf voltage. It will be off during the other half.

So the current in the inductor will be a pulsating direct current, and the Light Emitting Diode will emit light whenever it passes current. It does dual duty, rectifying the rf and emitting light in this application.

iceng (author)2017-07-01

no resonance

Deleola (author)2017-05-17

A commendable efforts. Well done. However, I am not sure what is wireless in this design. The circuit is still hooked onto 6v source. My idea of a Wireless POWERED System is not what is displayed here. This unit is powered by the attached 6v supply.

Anyway it is a nice attempt! Cheers

john henry (author)2016-03-22

Sorry but I can tell this is a poor design just my looking at it.. no wonder some people comment it doesn't work..

Those are not even a true coils.. might a well be a single unwound wire..
cap and inducer isn't even necessary for a transmitter.
This can definitely be made simpler...

AdelB1 (author)john henry2017-01-01

can you give me some pointers on how to make the simpler design of yours, thanks

neelandan (author)2011-06-18

And, I forgot to mention - y'all've been rick rolled.

mazoo (author)neelandan2011-09-01

So what you are sayin is that this is a fake???

I tried VERY hard to duplicate this with very hard to find...imported BF494 transistors, 104 z cap etc. etc. etc...........nada....!

suggestions? rick?

i have make this project and have working yes

Awesome-aniac (author)neelandan2011-06-19

That won't help your ratings...

neelandan (author)Awesome-aniac2011-06-19

The music in that video is the tune of "Never Gonna Give You Up" by Rick Astley. It was a favourite trick long ago in the internet to trick people into clicking on the link of the video, disguised as something else.

That comment was just to acknowledge the source of that music.

Awesome-aniac (author)neelandan2011-06-19

Ha ha, yeah, I know what 'rick rolling' is. It's just not what I want to hear in an instructable.

Soumojit (author)2015-08-26

can I use a 9v battry?

Antonius VincentM (author)2014-11-26

if i use TIP 31 and 3mH inductor can it still working please help me

Antonius VincentM (author)2014-11-26

if i use TIP 31 and 3mH inductor can it still working please help me

Antonius VincentM (author)2014-11-26

if i use TIP 31 and 3mH inductor can it still working please help me

Antonius VincentM (author)2014-11-26

if i use TIP 31 and 3mH inductor can it still working please help me

electro18 made it! (author)2014-08-29

Thanks for the great instructable ! I've posted an i'ble based on your project !

djc311 (author)2014-02-12

I'm still trying to figure out if there's anyway possible to make a "nano" sized (approx 3-4mm square) receiving device that could light a single LED. Any ideas or suggestions?

Cyberscann54 (author)djc3112014-08-15

I do believe it to be very possible heck take a smt led solid wire make a small coil solder to led tune transmitter circuit to pulse a optimum frequency and wala micro wireless led to make even better attach a smt capacitor and since you want it that small you could take tiny magnets and a dry erase board make a loop of wire the size of the board use about 10 to 20 loops place behind the board and have a very cool bultin board with wireless led lighting

djc311 (author)Cyberscann542014-08-15

I've seen these micro inductors that someone told me about but unfortunately I'm not quite savvy enough to figure these things out on my own very well.

I have two applications I'm trying to work with. One would put a single led approx 2-3 inches away from a standard 110vac power line and I'd like to make an led light up wirelessly (without needing big components)

The other application is probably more challenging because it needs to be incredibly small - at least the receiving led portion.

If you can, I'd like to see what you'd suggest to make this work.

SKtesla (author)2014-06-21

Hi. I tried building this and it didn't work. i used a 470 microHenry inductor, otherwise the circuit is the same. The transistor is not getting warm. Any idea why it is not working? Is there any way I can test the circuit? Thanks

GreeceFallout (author)2014-04-01

I didn't manage to make it work , I used a 9v battery downed by an lm317 to ~5v but none of my leds worked , made the antennae with copper wire ... I'm sure it works but...
yeah... Any tips ?

jbrown120 (author)2014-01-01

Will post results using skylanders portal of power and LED when I try this later

mugono08 (author)2013-11-01

At what frequency is the circuit resonating? I manage to build it and its working but i made my onw coil so i don't know the frequency

yaly (author)2013-10-04

I'll try and use a large transistor as TIP122 with 12v

neelandan (author)yaly2013-10-06

Won't work, it is too slow to operate at rf.

brunodiaz20 (author)2013-07-20

"blue LED" is infra red

yvarcot (author)2013-05-28

does the primary coil have to be the same size as the secondary coil?if we increase the voltage and the size will it solve the size problem?

MEHRAN CHAMANI (author)2013-04-11

Another example of this circuit
See it

Physicsperson (author)2012-08-07

Would a STS9013 transistor work?

cardboardwizard (author)2011-07-28

This is really nice, but what frequency does it make/run at.

I have not measured it.

But, from another project of mine it is probably running around 300 Mhz or so.

robotkid249 (author)neelandan2011-12-08

Trust me, It's not running at 300Mhz. We would probably be dead.. lol Even so, 300 Mhz would not be an efficient frequency to transfer power wirelessly.

kimvellore (author)robotkid2492012-03-18

Dont worry you wont die at 300MHz, Your cell phone runs at 800MHz to 2.6GHz and you can light a LED from that transmission, There are many fancy antennas that you can connect to your cellphone that light up when transmitting. Having said that the transistor BF494 is a medium frequency TR having a transition frequency of 120MHZ so it would be most efficient ~20-30MHz, so it is not running at 300Mhz..
For efficient transmission of power you should be able to concentrate power from the transmitter to the receiver without radiating all over so microwaves are perfect because they can be made directional and they start at 300mHz, There are recorded efficiencies of over 90% for power transmission using microwave.

nerd7473 (author)2012-01-11

where do you get a inductor?

M-Taimoor (author)2011-10-21

But neelandan, which transistor you have used in this circuit

M-Taimoor (author)2011-08-29

But what transistor you have used in it

GenAap (author)2011-08-21

could more coils improve the range on this? or would you have to change the circuit altogether?

pandyaketan (author)2011-08-16

Excellent, 5 *s !


"May the good belong to all the people in the world.
May the rulers go by the path of justice.
May the best of men and their source always prove to be a blessing.
May all the world rejoice in happiness.
May rain come in time and plentifulness be on Earth.
May this world be free from suffering and the noble ones be free from fears"
---- Vedic blessing

Sparkytastic (author)2011-06-28

I used a 2N3904(Base, Emitter, Collector are arranged different from the BF494) transistor and a 1000 mH inductor but it did not function. The transistor became warm (not hot) and it wouldn't effect the LED.

neelandan (author)Sparkytastic2011-06-28

The 2N3904 is a low frequency transistor and will not work in this circuit. The frequency of oscillation is a few hundred megahertz (about 300 MHz or so) and so a high frequency transistor is essential.

Sparkytastic (author)neelandan2011-06-28

I must have missed that on the datasheet. My bad.

EdurusFas (author)2011-06-19

I agree about the Rich Astley thing: it's like you made a fake instructable, and used Astley's music to indicate as such.

neelandan (author)EdurusFas2011-06-19

The circuit works.

I made the movie by taping the circuit to the table, putting the LED on the drawing of the circuit, then sliding it back and forth to show the LED lighting up and extinguishing.

Then, while searching around for some music to go with it, I found this tune of "Never Gonna Give You Up" and thought that it would be cool.

That comment was just to acknowledge the source of the music, and just why it is so famous on the net.

About This Instructable



Bio: I'm Chandra Sekhar, and I live in India. I am interested in electronics, and building small one-off circuits around tiny chips (the electronic kind).
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