Introduction: Light Activated Blinking LEDs

About: Student @ University of North Texas working towards a Mechanical and Energy Engineering Major. I do all kinds of fun little projects. I'm currently trying to scavenge old pictures so I can publish a few more o…
In this Instructable I will show you how to put together a flashing LED circuit that turns on when you wave your hand over it, blinks for a second or two, and then fades out.

I got the schematic for the flashing circuit from steven123654's instructable which can be found at:

I have since modified the circuit to include a light dependant resistor that is used as a momentary switch.

Step 1: The Idea

Besides being a fun project, and a great first LED project, if you make 5-10 of these circuits and put them together, it creates a pretty awesome wave effect as you pass your hand over each module.

I found the idea for this circuit on youtube. someone had made a table of LED modules that flashed as they cast shadows on the table. It looked pretty cool but I decided that it would be more fluid looking if there were more individual modules instead of large squares of LEDs all activating at once so I went to work and came up with this circuit.

Here's a list of the recommended parts:

-a breadboard
-100K ohm potentiometer
-a 3904 NPN transistor
-22 micro Farad capacitor
-1000 micro Farad capacitor (minimum, I use two caps and one is a 2200 uf)
-an LED
-a light dependent resistor
-two 1K ohm resistors
-one 100 ohm resistor
-a 555 timer IC
-a bunch of wires to connect it all

I'm pretty sure all of these parts can be bought at RadioShack.

If you already have the stuff check out the schematic on the next page to get started.

Step 2: The Flashing Circuit

This page shows the basic timer circuit used. It's a bit less complex than the full schematic and you may find it helpful to take it one step at a time, just to make sure you get it right.

Step 3: The Schematic

This is the schematic for my modified flashing circuit. as you build it, feel free to change out parts for others of different values. The potentiometer will definitely need to be adjusted, but after some tinkering you will get it right.

Make sure that it is in moderate to bright light when your playing with it. I'm not sure if the potentiometer can adjust far enough to allow it to work in darker rooms.

You may have to refresh the page to see the notes on my schematic.

Step 4: The Challenge

Hope you guys have fun with the project. If you come up with any cool uses/variations for it I'd love to know!