555 Timer: Running LEDs (Knight Rider)
This circuit creates a light that "runs" back and forth using a 555 timer and a decade counter. It's effect is similar to the light bar on the car from the old television show Knight Rider.
It's a really fun circuit to build. I once built a larger version of this for the inside of a party bus when I was a teenager. Unfortunately, I broke it the first day because I increased the voltage too much! But that's another story…
The Circuit
This circuit consist of two main parts; an oscillator and a counter.
The oscillator is built from a 555 Timer set up in astable mode. It creates a pulse train of 10 pulses per second.
The counter is a CD4017 that has 10 outputs. Each output indicates how many pulses it has received. For example after three pulses, output 3 is HIGH and the rest are LOW. The outputs are connected to six LEDs in a way so that LEDs 2 to 5 turn on both as it counts from 1 to 4, but also from 6 to 9.
Parts List
How To Build
You'll need a big breadboard for this one. Build the 555 circuit first and test that it works. Then connect the CD4017 and the LEDs below.
