In this 4017 Knight Rider circuit, the 555 timer is wired as an oscillator. It can be adjusted to give the desired speed for the display. The output of the 555 is directly connected to the input of a Johnson Counter (CD 4017).
The input of the counter is called the CLOCK line. The 10 outputs become
active, one at a time, on the rising edge of the waveform from the 555.
Each output can deliver about 20mA but a LED should not be connected to
the output without a current-limiting resistor (220Ω in the circuit
above).
The first 6 outputs of the chip are
connected directly to the 6 LEDs and these “move” across the display.
The next 4 outputs move the effect in the opposite direction and the
cycle repeats. The animation above shows how the effect appears on the
display. Using six LEDs, the display can be placed in the front of a model car to give a very realistic effect. The outputs can be taken to driver transistors to produce a larger version of the display.
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