Traffic lights with a 555 timer

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Traffic lights with a 555 timer

Information

The circuit consists of a 555 timer and a 4017 Johnson counter. The 555 timer sends pulses (0.47 Hz) to the Johnson counter, which changes output. By connecting some outputs together the timing of the light signals can be controlled. Four steps are used for the green LED and two for the yellow. The red LED is connected to pin 12 which is active for the first five steps. The white LED shows the pulses from the 555 timer.

Light signals

In sequence:

  • Red
  • Red and yellow (short)
  • Green
  • Yellow (short)

Sequence restarts.

Images

Schematic drawing

Traffic-ligts.png

Parts list

Qty. Part
1 Capacitor, aluminium electrolytic, 47 µF, 25V
1 Capacitor, metallized polyester foil, 6.8 nF, 63V
1 Capacitor, metallized polyester foil, 0.01 µF
6 Diode, small signal, 1N4148/Ph
1 Johnson decade counter, 5-stage, 4017, DIL-16
1 LED 5mm, Green, 2.0V, 10mA
1 LED 5mm, Red, 2.0V, 20mA
1 LED 5mm, Red/Green, 2.0 2.1V, 10mA, 100 63mcd, 30°
1 LED 5mm, Yellow, 2.0V, 25mA
32 cm2 PCB, stripboard, 100x160mm, 160cm2
1 Resistor, carbon film, 0.25W, 10 kΩ, 5%
2 Resistor, carbon film, 0.25W, 22 kΩ, 5%
1 Resistor, carbon film, 0.25W, 100 kΩ, 5%
4 Resistor, metal film, 0.6W, 1 kΩ, 1%
2 Straight pin header, male, Single row, 2.54mm
1 Timer IC, NE 555, 0/+70 °C, DIL8