Jun 092015

Electronic two-way traffic light Circuit

This Electronic two-way traffic light circuit achieves the functionality of a typical two-way traffic light using two integrated circuits: the 555 timer and the CD4017 decade counter.

How the Electronic two-way traffic light works?

The CD4017 integrated circuit has 10 outputs (0 to 9) which are activated sequentially (high
level). The speed of this sequence is given by the 555 timer output (clock) The 555 CI is working as an astable multivibrator, and uses a potentiometer to change the duty cycle from 2.5 seconds to 90 seconds.

Electronic two-way traffic light Circuit

The diagram above shows the connection of circuit components. The sequence of lights are in the following table.

Electronic Two-Way Traffic Light Sequence

From the table we see that:

  • The time that the green light is on is 4 clock cycles
  • The time that the red light is on is 5 clock cycles and
  • The time that the yellow light is on is 1 cycle.

The red light is on, one more cycle, than the green light. This is because, when the light changes from red to green, this is done without going through the yellow light. When the light changes from green to red, the yellow light is always displayed.

Analyzing the chart we can see the light sequence as CD4017 outputs are activated. These outputs can be applied to various LEDs in series using a transistor as shown in Figure. To handle greater loads we can use relays.

For route # 1

  • G1 = green
  • R1 = Red
  • Y1 = Yellow

For route # 2

  • G2 = green
  • R2 = Red
  • Y2 = Yellow

6 similar circuit could be connected to the G1, G2, R1, R2, Y1, Y2 outputs with corresponding LED

555 IC diagram and pin-out description

555 Timer Pin Description - Electronic two-way Traffic Light

CD4017 IC diagran and pin-out description

CD4017 Decade Counter Pin Description - Electronic two-way Traffic Light

  • Pins 1 to 7 and pin 9 and pin 11 are outputs for the counter.
  • Pin 8 is the negative power supply.
  • Pin 12 is the carry-out pin.
  • Pin 13 is the enable pin.
  • Pin 14 is the clock pin. This will be connected to the astable 555 timer.
  • Pin 15 is the reset pin. This returns counter to zero.
  • Pin 16 is the positive power supply pin.

List of components for the Electronic two-way traffic light Circuit

  • 16  red LEDs, 16 green LEDs, 16 yellow LEDs.
  • 12  1N914 diodes.
  • 6  2N2222 transistors (T).
  • 1  10 uF capacitor (C2).
  • 1  100uF electrolytic capacitor C1 (20 volts or more).
  • 1  100K Potentiometer (P).
  • 1  4.7K resistor (R1).
  • 1  1.5K resistor (R2).
  • 6  560 ohms resistors (R3,R4,R5,R6,R7,R8).
  • 1  555 timer.
  • 1  CD4017 decade counter.


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