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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.
wireless LED.wmv694 KB
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Signing UpStep 1The 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.
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.
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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.
But, from another project of mine http://www.instructables.com/id/UHF-oscillator/ it is probably running around 300 Mhz or so.
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.
I tried VERY hard to duplicate this with very hard to find...imported BF494 transistors, 104 z cap etc. etc. etc...........nada....!
suggestions? rick?
That comment was just to acknowledge the source of that music.
reg
ketan
"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
Thoughts?
I must have missed that on the datasheet. My bad.
Thanks!
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.