Neven's Electronics Page

Sweeping LEDs

This circuit flashes 7 LEDs in a manner similar to Knight Rider, the light moves from the leftmost LED one by one to the rightmost LED, then again back to left and so on, sweeping constantly from one side to the other.

A demonstration of circuit functioning

circuit diagram

NE555 is connected as an oscillator whose frequency can be changed by changing the 470k resistor or 220nF capacitor. It's output is fed to the clock input of 74161, which is 4-bit synchronous binary counter with load, asynchronous reset and ripple carry output. Outputs from the counter are connected to the inputs of 74154, 1-of-16 inverting decoder/demultiplexer which drives the LEDs. 74154 always has just one of it's outputs at logic "0" while all the other are at logic "1", so that always just one LED is on. As the counter counts pulses from NE555, with every clock pulse 74154 switches it's next output to logic "0" until it comes to the Y12. Logic zero at Y12 resets the counter and process starts all over again.

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