This one came to me out of the blue the other day while I was at work. A Christmas card with some LEDs inside that got power from a USB port. How geek is that?!
I decided that the LEDs needed to blink so I dug out my supply of 555 timer chips and built an astable circuit to to the job. I connected two different colors of LEDs to the output on pin 3 of the 555. The green ones have the anode (positive) side connected to pin 3 and the cathode (negative) connected to ground. The red LEDs have the cathode connected to pin 3 and the anode connected to the 5 volt positive rail. This allows the red LEDs to light when pin 3 is high, and the green LEDs to light when pin 3 is low. The blue LEDs are connected directly to the 5 volt power supplied from the USB cable. When you plug the cable into a USB port on a computer that is powered up, the LEDs flash.
Below you’ll find a parts list, a schematic, a build video with an explanation of the circuit and JPEG files of the templates to build the paper box. This is an easy and fun holiday project to build for the geek in your life!
Merry Christmas, have fun and…
Keep on hackin!
2 – 1.2K ohm resistors
1 – 470 ohm resistor on pin 3 output
1 – .01 uF ceramic capacitor
1 – 220 mF electrolytic capacitor
1 – LM555 timer chip
1 – USB cable
15 – Green LEDs
13 – Red LEDs
4 – Sheets 8.5″ x 11″ white card stock paper
Two sided adhesive tape
Hot glue and glue gun
Small perf board.