In this project we are going to design a circuit, to make a flashing light similar to that on a police car. This police light circuit is designed by 555 Timer IC and a decade counter IC. The timer here generates pulses which are fed to the 10-stage decade counter, the output of the counter is so arranged to get a flashy light like a police car.
+5 to +8v supply voltage
1KΩ, 10KΩ and 220Ω resistors (7 pieces)
10µF capacitor, 100µF capacitor (not compulsory, connected in parallel to power).
2N3904 or 2N2222 transistor (2 pieces)
RED LED (2 pieces) and BLUE LED (2 pieces)
- Components List
- 1x – NE555 Bipolar Timer
- 1x – 4017 Decoded Decade
- 6x – 1N4148 Diode
- 1x – 1K Resistor (1/4W)
- 1x – 22K Resistor (1/4W)
- 2x – 4.7K Resistor (1/4W)
- 6x – 470 Resistor (1/4W)
- 1x – 2.2 F Electrolytic Capacitor (16V)
- 2x – LED (Blue)
- 2x – LED (Red)
- 2x – BC547 NPN Transistor
- 1x – 9V Voltage Battery
The diagram for police lighting is seen in the figure above. The timer produces flashes of roughly 100ms. The time of ON is 50ms, and the time of OFF is 50ms. You can change this time by adjusting the capacitor value.
The binary counter now counts the number of pulses indicated in a clock and causes the resulting pin output to go up, e.g., if the event count is 3, then a counter pin of Q2 is high, and if 5 counts, the pin of Q4 is high. The counters of both pulses will be calculated as the counter pin of the case. So there would be a peak for every 100ms for this peak, and so is the output.
Here, one transistor is attached to Q0, Q2, and Q4, and another transistor base is attached to Q5, Q7, and Q9. A RED LED is driven with the first transistor, and a second powers a range of blue LEDs with the second transistor.
As stated earlier, one counter output per 100ms is increased until the excess flow. The counter resets and starts from zero again when the count is overflowed.
Applications and Uses
A police light is a form of emergency lighting for cars. In ambulances, fire brigades, armed cars, etc., you can even see the same blinking lights.