Introduction
Police Lights are flashing lights which are a type of emergency vehicle lighting. You can also find similar flashing lights in ambulances, fire department, military vehicles etc. They are visually captivating and often convey the state of urgency of their task to the other road users. In this project, we will just take the visual aspect of the police lights and implement them in our own way. The circuit uses 555 timer and a decade counter IC CD4017. Here, the 555 timer runs in Astable mode. Decade counter 4017 counts the incoming pulses and activates its outputs i.e. for the first pulse Q0 becomes high and for second pulse Q1 becomes high and so on again for 10th pulse Q0 state becomes high.
555 Timer Based Police Lights Circuit Principle
Here 555 timer produces continuous pulses via pin 3. The width of these pulses can be varied by varying the resistance (R1,R2 ) or capacitance (C1). These pulses are given as input to the decade counter. For every incoming pulse the output state of the decade counter is get incremented.
For 1st pulse – Q0 high – blue led’s glow For 2nd pulse – Q1 high (no connection) – all led’s off For 3rd pulse – Q2 high – blue led’s glow For 4th pulse – Q3 high – all led’s off For 5th pulse – Q4 high – blue led’s glow For 6th pulse – Q5 high – red led’s glow , blue led’s off Hence blue led’s flashes for 3 times. For 7th pulse – Q6 high – all led’s off For 8th pulse – Q7 high – red led’s glow For 9th pulse – Q8 high – all led’s off For 10th pulse – Q9 high – red led’s glow For 11th pulse – Q0 high – blue led’s glow, red led’s off
Hence, red LEDs flash for 3 times. This process repeats continuously.
Circuit Diagram of Police Lights using 555 Timer
Circuit Components
555 Timer IC 4017 Decade Counter IC 1KΩ Resistor (1/4 watt) – 3 22KΩ Resistor (1/4 watt) – 1 470 ohm Resistor (1/4 watt) – 6 2.2µF Electrolytic capacitor (16V) – 1 BC547 NPN Transistors – 2 Blue LEDs – 2 Red LEDs – 2 9V battery – 1 Connecting wires
555 Timer based Police Lights Circuit Design
555 Timer
Here, 555 timer runs in free running mode i.e. Astable Mode. It produces pulses whose width can be varied. 2nd and 6th pins are shorted to allow triggering after every cycle. 4th pin is connected to Vcc to avoid sudden resets.
4017 Decade Counter
It is a 10 bit counter with ten decoded outputs. It counts the incoming pulses. The supply voltage range is -0.5 to +22V. The high pulse on the reset pin clears the count to zero. The speed of operation of this IC is up to 10 Mhz. The ouput states (Q0,Q2,Q4) are configured to flash the blue LED’s 3 times and the states Q5, Q7 and Q9 are configured to flash the red LED’s 3 times. Based on the outputs of 4017 IC, two transistors (NPN) switches the LED’s ON and OFF. Resistors R3, R4, R5, R6 are used to protect the LED’s from high voltage. Circuit Simulation Video
How to Operate Police Lights Circuit?
Apply power to the circuit. Now observe the LED’s, red led’s flashes 3 times and blue led’s flashes 3 times and this process repeats. If you want to set the different time delays for LED’s then vary the resistance (R1, R2) or capacitance (C1).
555 Timer based Police Lights Circuit Applications
This circuit used as an indicator for police cars. We can use it as LED flasher circuit by making some modifications.
Limitations of Police Lights Circuit
The values of the resistors R1, R2 and capacitor C1 should be same to get perfect flashing.
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