In this project, I will demonstrate how to create a police lights effect using 555 Timer and CD4017 Counter ICs. This circuit simulates the flashing lights seen on police cars by alternating between flashing red LEDs three times and blue LEDs three times before repeating the sequence.
Outline
- Introduction
- 555 Timer Based Police Lights Circuit Principle
- Circuit Diagram of Police Lights using 555 Timer
- Circuit Components
- 555 Timer based Police Lights Circuit Design
- 555 Timer
- 4017 Decade Counter
- How to Operate Police Lights Circuit?
- 555 Timer based Police Lights Circuit Applications
- Limitations of Police Lights Circuit
Introduction
Flashing lights, commonly referred to as police lights, are a type of emergency vehicle lighting used by ambulances, fire trucks, military vehicles, and other similar vehicles. These lights serve both functional and aesthetic purposes, conveying the urgency and importance of the vehicles’ missions to other road users.
In this project, we aim to capture the visual appeal of these lights and incorporate them into our own design. To achieve this, we utilize a 555 timer and a decade counter IC CD4017. The 555 timer operates in Astable mode, generating a continuous pulse signal. The CD4017 decade counter counts the incoming pulses and activates its outputs sequentially. For example, Q0 goes high for the first pulse, Q1 goes high for the second pulse, and so on, until Q0 goes high again after the tenth pulse.
555 Timer Based Police Lights Circuit Principle
The 555 timer generates continuous pulses via pin 3 in this example. The resistance (R1,R2) or capacitance (C) can be changed to alter the pulse width (C1). The decade counter receives these pulses as input. The output state of the decade counter is incremented for each incoming pulse.
- 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
In this configuration, the 555 timer operates in its free-running mode, also known as Astable Mode. It generates a series of pulses with adjustable pulse widths. Pins 2 and 6 are connected together to enable triggering at the end of each timing cycle, ensuring continuous operation. Additionally, the 4th pin is connected to Vcc to prevent unintended resets.
4017 Decade Counter
It has ten decoded outputs and is a ten-bit counter. It keeps track of the incoming pulses. -0.5 to +22V is the supplied voltage range. The reset pin receives a strong pulse, which resets the counter to zero. This IC can operate at a frequency of up to 10 Mhz.
The blue LEDs are flashed three times in the output stages (Q0,Q2,Q4), whereas the red LEDs are flashed three times in the output states (Q5, Q7, and Q9).
Two transistors (NPN) switch the LEDs on and off based on the outputs of the 4017 IC.
To protect the LEDs from high voltage, resistors R3, R4, R5, R6 are employed.
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.
