Sunday, May 17, 2009

Wireless LED throwies

I was digging around in the junkbox and decided to make some wireless LED throwies maybe whynot?

I used a modified ATX power supply, a 555-chopped MOSFET pulled from an old monitor, and coil made from magnet wire salvaged from a blender motor.

The transmitting coil was fabricated by putting some nails into a peice of wood and wrapping to get a consistent shape. When powered by the driver it generates an alternating magnetic field which can picked up by other nearby coils.

Throwie #1:
A a ferrite-core inductor, a diode, a capacitor, and LED. Half-wave only so it has to be right-side up.

Throwie #2:
An RF choke from a vacumn tube oscilloscope, and two LEDs. Rectification is by the LEDs, so it isn't polarity sensitive.

This spider has a choke for an abdomen and the legs make up the bridge rectifier.

Throwie #3:
A coil of hair-thin magnet wire with a diode, and LED. Polarity sensitive.

Throwie #4:
Space ship with bridge rectification from quad 4148 diodes. Very effecient b/c of large receiver and full-wave rectification, works in almost any orientation.

Throwie #5
Spider has choke receiving abdomen and the legs form a bridge rectifier. Four SMD LEDs for eyes in series to cut the voltage some.

Works through paper, plastic, thin metal, etc. Magnetic fields are not stopped as easily as electric fields :)

Here's a clip on the throwies in action:


Katy said...

Thanks for your pics and diagrams, I have tried to make this for a theatre production but am not having much luck!
I have checked the driver circuit and cannot see any faults, but am not able to get the 'throwie' to respond.
Should I be able to meter a voltage across the two ends of the driver coil? I am able to get an LED to light up when put it directly between pin 3 and +12v (with the 10ohm R in place), but am not able to detect the correct voltage when I put the coil in place, even with the n-channel in series.
Without the coil in, I get reading of 12.39v between +12 & -12, 13.03v between +12v & S pin of n-channel, and 5.43v between +12v & pin 3.
With the coil in place, I get rapid fluctuation between 0.4v and 2.1v across +12v to ground (earth in wall socket) and 0v across the two ends of the coil.
I hope this makes sense, and doesn't show me up as too much of an electronics dunce! I have a fair basic understanding but this has stumped me!
Any ideas would be so gratefully received, as I have to get this working this week!

Anonymous said...

Can you make a radio shack parts list for us? It would be very helpful. Thanks!

Eric said...

yeah parts list would be awesome.. especially for someone waaaaayyyy behind as a beginner.

Anonymous said...

Thanks for the pictures and the schematic diagrams, but can you make a parts list? It would really be helpful :)

P.S. Thanks for sharing us your projects^^

Glenn Hackleman said...

Katy - you need to see if it if the circuit is oscillating. Hook a small piezo or tweeter speaker to the output of 555 timer (pin 3) and ground. You should be able to hear a high pitched whine.

janoo said...

I am talking about input side, It is only a coil which is connect to voltage. I mean if I connect the voltage to the primary coil without any network(RLC), whether it will work.PLZ tell

Levi said...


Is it possible to have a metallic plate with current running through it (Let's say one large battery or AC power) and just have magnets attached to the LEDs so that when you toss them onto the plate they would light up?

Glenn Hackleman said...

No a plate wouldn't do anything, the current needs to be driven through a wire loop to create a magnetic field.

Arnav Dhamija said...

Hi, I'm building a similar wireless electricity transfer project using a 555-IC. It was a pleasant surprise to find your blog relating exactly to the same thing!

I wanted to ask why exactly you've put the MOSFET in series with your primary coil. Moreover, how did you change square wave DC from the IC555 to square wave AC?

Glenn Hackleman said...

The Mosfet is in series with the coil to switch on/off the flow of current to the coil.

The square wave DC *is* technically AC. AC is simply alternating current. That means it alternates between two voltages. These extremes do not have to to be different polarity to be AC. You are probably most familiar with household wall sockets which may be 120 or 220 Volts AC depending on where you live. In that case the voltage alternates between +120 volts and -120 Volts (RMS). In my case the Alternating values are are 0 volts and 12 volts. Make sense?