The led chaser is build on a perfboard using 10 leds, CD4017 decade counter, a 555 timer configured in astable mode and some additional components. The circuit is really simple. On the left we see the NE555 timer IC configured in astable mode, producing a squarewave which frequency is defined by the resistor array and C1 capacitor. Trimming R4 we are able to change the velocity of the running LEDs.
The output of NE555 timer is feed to CLK of 4017 decade counter. So in practice decade counter is counting the pulses that NE555 produces and for each pulse one LED is lighting. On the next pulse the first LED is shut of and the next is light up. This continues until the last led is ON and the sequence continues from the first one.
So if you arrange the LED in a closed shape the LEDs will spin forever.
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