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Led Circles

This is simple yet impressive project that I built for Diwali/ Halloween 2009



Parts needed:

  1. Red Led
  2. Blue Led
  3. Two CR2032 (3V button cell from Radioshack)
  4. 1.5-3v Motor( 5000 rpm no load from Radioshack)
  5. Power Supply
  6. Some Cardboard
  7. Scissors
  8. Tape and thats it!!!



  • First draw a circle of required radius on the cardboard and cut it with scissors
  • From the center of the circle mark two points which are roughly equal to 1/3R and 2/3R where R is the radius of the circle. Make sure that there points are on either side of the center. I shall explain the reason for that later
  • Make holes big enough that the led legs can pass through them. The Blue led will go at the hole which is at 2/3R and the Red at the hole which is 1/3R.
  • On the Rear side tape the Blue led to the battery such that the longer leg of the led ( anode) is connected to the positive of the battery and the shorter leg of the led (cathode)  is connected to the negative end of the led.
  • Since the forward voltage of blue led is around 3.3V you can safely connect it directly to the battery.
  • However since the forward voltage of red led is around 1.7V connecting it directly to the 3V battery will burn the led. Hence we need to use a 68 ohms 1/8 watt resistor in series. Here's a good website to find out led series resistor required. So you solder the positive terminal of the led to one terminal of the resistor. The other terminal of the resistor is taped to the positive end of the battery. The negative end of the battery is connected to the cathode of the led.
Here's how it should look



Front View
Back View



  • Make a hole in the center so that the shaft of the motor can pass through. I used a washer and tape to seal the front hole of the cardboard. This was done because the speed of the motor eventually makes the hole in the cardboard big causing the card board to spin off the motor. Well ya it wasnt the best possible design. I am sure you guys can do a betterjob with it.
  • Now coming back to my point of having the holes on either side of the center. This helps in better load division. The attempt here is to make the load balanced on either side of the center so get more efficency and result. You might see wobbling effect if all the load is on one side.
  • I used the variable smps power supply that I own to drive the motor. Since I had a minimum setting of 3.3V on my power supply I had to use a small resistor to limit the current. Though u can drive the motot with the CR2032 battery itself however these batteries cannot provide enough current to drive the motor under load condition.
And thats it.. You are done..... Lets see action.....

Led Circles In Action




Led Circles at the window of my house



And yes if you  some funny people doing crazy stuff in this video they are my roommates... who were helping me in this project :)

Hope you guys liked it

KD



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