KNIGHT RIDER Circuit
In the
Knight Rider circuit, the 555 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 Q
0 to Q
9 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 (330R 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 3mm LEDs, the display can be placed in the front of a
model car to give a very realistic effect. The same outputs can be
taken to driver transistors to produce a larger version of the
display.
Here is a simple Knight Rider circuit using resistors to drive the
LEDs. This circuit consumes 22mA while only delivering 7mA to each
LED. The outputs are "fighting" each other via the 100R resistors
(except outputs Q0 and Q5).
