TRAFFIC LIGHT SYSTEM USING IC555

By Creative Engineering Projects on 12:29 in 2nd semester, 4017 decade counter, analog, engineering project, ic555, traffic light

Abstract:

Ø This project operates red, amber and green LEDs in the correct sequence for a single traffic light.

Ø The time taken for the complete red - red & amber - green - amber sequence can be varied from about 7s to about 2½ minutes by adjusting the 1M preset.

Ø The 555 Astable circuit provides clock pulses for the 4017 counter which has ten outputs (Q0 to Q9).

Ø Each output becomes high in turn as the clock pulses are received. Appropriate outputs are combined with diodes to supply the amber and green LEDs.

Ø The red LED is connected to the ÷10 output which is high for the first 5 counts (Q0-Q4 high), this saves using 5 diodes for red and simplifies the circuit.

Components used:

Circuit diagram:

Working of components:

· IC555:

Ø It works in 3 modes:

v Astable - producing a square wave

v Monostable - producing a single pulse when triggered

v Bistable - a simple memory which can be set and reset

v Buffer - an inverting buffer (Schmitt trigger)

Here in this project it is operated in Astable mode.

Astable State:

An astable circuit produces a 'square wave', this is a digital waveform with sharp transitions between low (0V) and high (+Vs). Note that the durations of the low and high states may be different. The circuit is called an astable because it is not stable in any state: the output is continually changing between 'low' and 'high'

v With the output high (+Vs) the capacitor C1 is charged by current flowing through R1 and R2. The threshold and trigger inputs monitor the capacitor voltage

v When it reaches ²/₃Vs (threshold voltage) the output becomes low and the discharge pin is connected to 0V.The capacitor now discharges with current flowing through R2 into the discharge pin.

v When the voltage falls to ¹/₃Vs (trigger voltage) the output becomes high again and the discharge pin is disconnected, allowing the capacitor to start charging again.

· 4017 decade counter:

Ø The count advances as the clock input becomes high (on the rising-edge). Each output Q0-Q9 goes high in turn as counting advances.

Ø Appropriate outputs are combined with diodes to supply the amber and green LEDs.

Ø The ÷10 output is high for counts 0-4 and low for 5-9, so it provides an output at ¹/₁₀ of the clock frequency.

Ø The red LED is connected to the ÷10 output which is high for the first 5 counts (Q0-Q4 high), this saves using 5 diodes for red and simplifies the circuit.

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