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Control Circuit for Traffic Light
The design of the circuit can be used to create a traffic light wherein twenty open collector that turns ON one at a time in a continuous sequential manner.
The 74LSxx family of TTL integrated logic devices is being used by the circuit which is designed to drive low current & low voltage incandescent lights or light emitting diodes but it can also drive other loads with until 80 mA. The construction of the 20-Step circuit is fairly simple but extra care should be observed when wiring the circuit due to the high speed nature of the TTL logic devices used.
An adjustable LM555 astable oscillator contains the sequence used for stepping the circuit. The output of the oscillator will be divided by a 74LS90 divider into a 10-step BCD weighted output. The output of the BCD will drive two 74LS145 which is 1 of 10 decoders. The decoders are used to produce 1 of 20 step output sequence. The two 74LS145 are driven by the circuit using four 74LS32 dual input OR gates and a 74LS107 JK flip-flop for controlling the output drivers by creating disallowed states in the output drivers alternately.