Introduction: Easy Wireless LEDs

Yes ! That's right , this instructable will guide you to create your own wireless LED.

This instructable is inpired from : Wireless L E D by neelandan ! Thanks for this great instructable !

This version uses a more powerful high frequency switching transistor ( BD139 ) so that means now you've got great power and " with great power comes great responsibility " :D

*So use this device with great caution and DO NOT use it near any sensitive electronic device ( specially hard drives ) as it is capable of creating high frequency EMPs which could easily mess with your gadget ! While working with transformers take proper safety measures and use an insulated casing as there may be a potential threat of getting electrocuted. ( Instead use a power adapter or a battery ).

This project is pretty easy to make and can be used to demonstrate and study the principle of electromagnetic induction practically . The components are pretty easy to get

all you need is :

1. 2 x 2 turn coils

2. 33k resistor

3. a 100nf capacitor ( code : 104 )

4. 100 µH ( micro Henry ) Inductor

5. An LED ( red / orange / SMD red works best )

6. BD139 transistor ( or equivalent )

7. A bridge rectifier ( optional I've used 1n4148 diodes )

8. A perfboard ( 3x3 cm )

9. Wires , solder , power source ( 6-12 V ).

Step 1: Gathering the Parts ->

1. Coils can be salvaged from old toroids

2. Transistor ( BD139 ) , Resistors ( 33k - orange // orange // orange ) and Capacitors ( 100nf - 104 ) are pretty common and can be bought from a local electronic hobby shop.

3. Inductors can be salvaged from old PCBs and can also be made by winding a coil around a ferrite core.

4. Make a mini bridge rectifier >> ( next step ).

Step 2: Mini Bridge Rectifier

You'll need 4 x 1n4148 diodes.

1. Follow the schematic and join the four diodes one - by - one.

2. Twist the wires ( pay attention to the polarity of diodes black lines denote negative terminal ).

3. Solder them together.

4. Your bridge rectifier is ready !

*I've used a bridge rectifier because I'm taking power from an AC source ( 6 - 12V ) but you can skip it and just use a battery.

Step 3: Soldering the Circuit


1.Follow the schematics and solder the circuit as shown ( on a perfboard ) .

2. You can also assemble it on a breadboard ( I recommend you to first prototype the circuit on a breadboard and then solder the final circuit ).

3. Be careful while soldering the coil and try not to deform it. The shape needs to be perfectly circular and planar.


1. If you're using an SMD LED then solder a pair of leads to the solder pads on the led.

2. In case you're using a through-hole LED , just solder it's leads directly to the coil ( don't worry about the polarity ).


This device basically works on the principle of mutual induction . The magnetic flux generated by the emitter coil gets linked to the secondary coil ( coil with LED ) due to this , EMF is induced in the coil.

According to the expression of induced EMF (rate of change of flux linked to the coil ) , the EMF induced in the secondary is directly proportional to the rate at which the current changes ( or switches ).

Also DC can't be directly induced using this method , this is because in DC , the current is constant throughout unlike AC current.

Commonly , the frequency of AC current that we get is 50-60 Hz which isn't enough to light up an LED using this process , so here comes the oscillator circuit which takes in power from a DC source and converts it into a high frequency switching current.

This is done by a high frequency power transistor ( BD139 ) which constantly switches , generating a high frequency switching current. This is then fed to the primary coil which converts this energy into a constantly changing magnetic field. This increases the frequency of the current and therefore the EMF induced in the secondary coil becomes enough to light up an LED.

You don't need to worry about the polarity of the LED because , the frequency of the current is so high that the human eye won't be able to identify the blinking effect ( due to persistence of vision ).



1. Hook up the oscillator to a DC power source ( 6- 12V depending on your transistor ).

2. Place the driver coil on a flat steady surface.

3. Hold the led coil such that both the coils are in parallel planes.

4. Bring the LED coil close to the oscillator coil ( do not bring it in contact ).

5. The transistor may heat up a bit , but that's fine !

5. Success !


1. Check the solder-joints.

2. Avoid touching any loose contacts on the oscillator board.

3. Make sure that the coils are circular and not deformed.

4. Hold the coils at an optimum distance.

5. If the coils are a bit tilted then the LED wouldn't glow so brightly.

Suggestions and corrections are welcome ! Feel free to ask your questions about this i'ble !


iceng (author)2017-07-01

no resonance

Chandan Kolaparthy (author)2017-01-05

Can I use 32AWG enameled copper wire for it? Please reply quickly I really need help


32 gauge is pretty thin for this project, the coils will deform easily if you use a low gauge wire. Though it should work just fine if you build something to support the coils in the desired shape.

THEbloxermanRBX made it! (author)2016-03-11

I made my self a inductor but not 100 mH and it's works fine

xILLYRIAx (author)2015-09-18

Will this power multple leds in a chain?

kingkaushal (author)2015-07-18

cool project

hamxa.abbasi.3 (author)2015-03-22

This is a 100 micro henery inductor , what 2 pins to use ?? I am finding it difficult!

electro18 (author)hamxa.abbasi.32015-03-22

It seems that the inductor that you've got is a common mode choke ( i.e couple of two discrete 100µH inductors with a common core ). Try using your DMM to check the resistance or continuity between every combination of two pins. At some point you'll get a certain amount of resistance and at some point you won't get any continuity. If the case is true then the pins which show some resistance are to be used as an inductor. The other two pins can be left open. This schematic should help :

ledvineeth (author)2015-02-24

hi im going to do this please give this video youtube link

electro18 (author)ledvineeth2015-03-05

The youtube video is already embedded on the very first step !

Akasi (author)2015-01-23

Hey, Akasi here again. I have built your circuit exactly as you said, except I used a breadboard and a 9v battery. I cannot get it to work! Please look at these images and tell me if there is something wrong!!! I need your help ASAP! Here are the pictures. The second-last picture is my receiving coil, and the last picture is what my DMM shows when I hook it up. Please reply!!! Thank you so much!

electro18 (author)Akasi2015-01-24

Okay , so it seems that you've got the circuit all right. Did you check all the connections with your DMM's continuity tester ? specially the coil joints ?

Also make sure that your transistor BD139 is in working condition ( just by making a simple switch with an LED ).

Be sure to use a coil made up of a thicker wire ( smaller gauge number ) and that it has 1~2 turns ( both the coils should be identical ).

Have you tested this circuit with an LED ? Because the DMM isn't capable of measuring such high frequencies ( not more than a few hundred Hertz ). So either you may hook the receiver coil to a bridge rectifier and then filter it using a 10uF - 100 uF capacitor.

Akasi (author)electro182015-01-24

Why can't the number of turns be more than 1-2? I was planning to put 10 turns in both coils, and test out what happens when we change the diameter and turns of the transmitting coil. Why does the gauge of the coil have to be low? What gauge do you recommend?

electro18 (author)Akasi2015-01-24

Because, as you increase the turns, the resistance also increases. We need to keep the turns minimum ( though 10 turns should probably work fine ) and a lower gauge wire is to ensure that the structure stays in shape ( when you're making the coils manually ).

The most important thing is that, did you test it using an LED before hooking the rec. coil to the DMM ? and is the transistor working fine ?

Akasi (author)electro182015-01-24

Yes,I did use the LED, and it didn't work. I tested the transistor using a switch circuit and it works fine.

electro18 (author)Akasi2015-01-24

Did you check all the connections using continuity tester ?

Akasi (author)electro182015-01-24

Good news! It works!!!!! Thank you so much! At this time, I cannot send photos, but I will once I record some data. I used 22 AWG wire, made 2 turns, stripped the wire well, and plugged it into the circuit, and it works!! Once again, thank you. I am eternally grateful towards you.

Keep making projects like this. I chose your project over everyone else's as you made it simple and explained how to make it throughly! You definitely have my vote!

electro18 (author)Akasi2015-01-24

Great job ! I'm glad to hear that ! :)

Thanks for the appreciation and support ! :)

Akasi (author)electro182015-02-27

I'll post the pictures soon. I am converting the AC current into a DC one to power a 3VDC motor, but the resulting DC current is too small. I decide to kick it up a notch and give the transmitting circuit 12 volts, but I am not sure if the components can handle that power. What do you have to say?

Mr AbAk (author)2015-01-08

Awesome ible...
We would surely make one...

electro18 (author)Mr AbAk2015-01-08

Thanks ! Good luck :)

Akasi (author)2015-01-01

What was your DC input and the resulting output (is it AC or DC) in the receiving coil? I was planning to modify this experiment to make a phone charger, and I wanted to know if there are efficiency losses, so that I can compensate for that.

electro18 (author)Akasi2015-01-02

While testing, I've subjected it to a range of input voltages ( ranging from 5V to 24V ) and obviously the induced EMF in the sec. coil directly depends on the input voltage. Just to measure the rms value of the AC induced on the other side, I hooked the secondary coil to a DMM and found out the value close to 54V ( at 21V input ). I can't say how accurate these values are or even is DMM capable of measuring high frequency AC but you'd require much more complex circuit which could deliver enough current for effective and fast charging of the Li-ion battery inside your device. I cannot guarantee the safety of this device either.

Akasi (author)electro182015-01-02

Okay, thank you. The kind of cleared things up. To charge a phone, I need at least 5V, and I was just deciding what kind of battery I should use to get that output. The second question I have is if the output current (secondary coil) is AC or DC. If it is AC, I think I will have to make that bridge rectifier to convert it into DC. Am I correct?

electro18 (author)Akasi2015-01-02

Yes, you're right, the current in the secondary is constantly alternating ( AC ). You'll need to connect the AC output to a bridge rectifier then filter the output using a capacitor and then finally regulate it to 5V either by a linear regulator or a buck converter ( I'd prefer a buck converter as it is much more efficient ). The input voltage solely depends on the transfer distance and the maximum rating of the particular transistor.

Akasi (author)electro182015-01-04

Oh wait, one more question. To convert the AC to a DC current, can't I use the phone adapter that we plug in to the power outlet? Wouldn't that convert DC for you. I understand that you need a specific input voltage, but that can be experimented with. Would this be a good way to convert AC to DC for charging a phone?

electro18 (author)Akasi2015-01-04

No, that wouldn't work at all. That's because, the cellphone charger is rated to get input at 230V or 110V ( nominal ) at 50~60 Hz. Normally these chargers have huge capacitors and a small transformer to convert the input voltage into 5V efficiently but if the potential difference across the transformer reduces, the output voltage will automatically decrease by a certain ratio. None of the given ratings match with the output AC in coil. The EMF produced is very less , the frequency lies in the radio range (10^6 times larger) and the current that can be drawn from it is low. That's why it won't be a good idea to feed the coil output into the phone charger. Rather you could use a 5V buck converter ( can easily be salvaged from a portable car cellphone charger ), a bridge rectifier and a couple of other passive components to effectively charge your phone.

lj1vukoder (author)2014-12-17

Would a 2N4401 transistor work as a replacement for the 139 transistor? Thanks!

electro18 (author)lj1vukoder2014-12-17

I haven't tried the circuit with 2N4401. Though, I did use a BC547 and BC847 ( which didn't work at all ). So, I don't think that 2N4401 would work either. The only transistor that I could use in this circuit was BD139, I don't exactly know the reason ( It maybe the max. current that the transistor can handle) and I can't surely say anything about 2N4401. I'll give it a try and get back to you soon.

Rohit Kumar Ranjan (author)2014-12-04

can you tell how this led glow on ac as we know it works on dc only?

and how much frequency this oscillator ckt is generating and what is the formula you used to calculate frequency?


Though the LED "appears" to be glowing continuously, it actually blinks many times in one second ( which is not noticeable to the human eye due to persistence of vision ). The current that is induced in the coil due to resonance is AC and the frequency can be calculated by f = 1 / ( (LC)^1/2 ). The frequency being very high, the LED rapidly shifts from forward bias to reverse bias, this causes it to blink extremely fast ( in the RF range ). This makes it look like the LED is glowing continuously.


ok but as we know that electron must take some time to reach conduction band from valence band, then how it is possible that it can reach to cb in that mean time?......


That actually depends on the maximum possible switching frequency of the particular transistor. That is the reason why we need BD139. If you try to make the same with a BC547 then it won't work. BD139 is specially fabricated to handle high frequencies.


ok you are saying that electron speed depends on frequency?....can you tell me how you can calculate f=1/(LC)^1/2 in this oscillator ckt? and which type of oscillator is this?


The formula 1/(LC)^1/2 is to calculate the angular frequency ( 2πf ). The frequency can be calculated by 1/2π(LC)^1/2.


In the formula, the C is for the capacitance of the capacitor and L is for the inductance of the circular coil. Though the values may differ, the accurate oscillation frequency can be calculated by using an oscilloscope.


i want know how you can derive that formula?

vallabh rao (author)2014-11-09

hey i made it ^_^ thanks a lot for a an awesome ible

electro18 (author)vallabh rao2014-11-09

I'm glad that you found it useful ! :)

And BTW, pure coincidence that I'm making this for my 12th standard project too ! :D

If you find my ibles interesting , please support by leaving a vote , it means a lot to me :) Thanks in advance !

vallabh rao (author)2014-11-09

i have a problem... its not working for me.. can yu please help me?

vallabh rao (author)vallabh rao2014-11-09

here is what i have done its connected to 9v battery

electro18 (author)vallabh rao2014-11-09

Okay , So it seems that you've swapped the Collector and Base pins.

The middle pin on the BD139 is "collector".

1. Desolder the other end of the coil and solder it to the collector ( middle pin on BD139 ).

2. Desolder the resistor, capacitor- junction from the middle pin and solder it to the base.

3. Arrange your coils properly and ensure that they are not deformed.

Hope this helps :)

vallabh rao (author)electro182014-11-09

thanks a lot for the great support. i used this for my 12th std phy project ;-) i am gonna remember you for ever in my life :-P

vallabh rao (author)vallabh rao2014-11-09

is this fine? but not getting the success :(

kamalkannan12 made it! (author)2014-11-03

I've done it with IRF540 instead of BD139. It works with 12V. I'm using the circuit which given below link

but there is a correction.. You need to connect both diodes in opposite direction if that circuit doesn't work.

transmitter circuit.jpg
electro18 (author)kamalkannan122014-11-03

Ah ! that was the exact thing that I was gonna do ( replace the transistor by a MOSFET ) ! Thanks for providing the schematics though ! :)

heath whibley (author)2014-10-11

Can you figure out another circuit without the transistor?

electro18 (author)heath whibley2014-10-12

I don't think that without a switching device ( a transistor ) the circuit would work. You can use any other equivalent transistor for this purpose if you're finding it difficult to get a BD139.

kamalkannan12 (author)electro182014-10-18

Can I use AC 12V as input and It still need a transister?

About This Instructable




Bio: Hey there ! I'm Tanay , a hobbyist interested in making robots and sharing stuff. I hope that my instructables help you in solving your problems ... More »
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