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Modified:21:22, 22 October 2013

You'll have to excuse the title, its a copyright thing. This circuit is similar to the light display that used to be on the front of a certain car in a certain American series. I am not a fan but the circuit below simulates the same light display used.

The PCB was designed to have the LEDs mounted on it. This saves on annoying wiring. These were bent over so they could be positioned in a front grill of a car - an MG in this case.

Shown left is the main part of the circuit. An astable formed by IC1a/b drives a 4-bit binary counter IC2, which is decoded by the 3-8 line decoder IC3, to provide the required sequenced outputs.
To make the sequence reverse, the up/down input to the counter is controlled by a bistable formed from IC1c/d. This sets the U/D input high when output 0 is high so that the counter counts up, then is toggled low by output 9 to reverse the direction of count. This is then repeated indefinitely giving an output chase backwards and forwards.

The speed of the chase can be adjusted by VR1 which alters the speed of the astable.


This section is repeated 10 times for each output (Out0-9), to increase current drive to the LEDs or bulbs. If using bulbs then change R12-21 with a link wire. The 2N3904 has a maximum current of 200mA. This can be replaced with a higher device such as TIP122 darlington giving over 1 amp capability. There will be a slight drop in output voltage due to the voltage drop of the extra transistor. The pin connections are the same.

The capacitor C2-11 gives the output a slow switch off time resulting in a blurred chase.


Finally D1 prevents damage through reverse power connection with C3 and C4 decoupling the supply.


The PCB shows the transistors being TO92 case. The pinouts are the same for many other transistors including Darlington types. There is room for the TO220 case of the TIP122 transistor.

If using bulbs as output devices then replace the 390ohm resistors in series with each output with a wire link.


Designed and Written by Phil Townshend 2009
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