Blinking Police Light LED Effect Using 555 Timer.

Overview

In this project we will build a blinking police light using 555 timer and CD4017 decade counter IC. Flashing police lights are designed to operate at different flash frequencies, usually alternating between different colors (most commonly red and blue), to attract the public's attention and visually communicate urgency and caution.

Flashing police lights are a symbol of authority and order. When the lights are flashing, it's an indication that an emergency is occurring and everyone in the vicinity should clear the way for law enforcement vehicles. They indicate that the vehicle is responding to an emergency and help alert other road users of the vehicle's presence, often at a great distance.

Earlier we built Heart Shape LED Strobe Light and Auto LED Blinking project using 555 Timer IC. The current project is also based on a similar concept.

Below are the components needed to create a blinking police light LED effect using a 555 timer.

555 Timer IC

CD4017 Decade Counter IC

Resistors: 10k ohms, 1k ohms and 220 ohms

Capacitors: 10uF and 100uF

Red and Blue LEDs (2 each)

Transistors 2N2222 (2 each)

Breadboard

Cable

The above circuit is designed for police lights and uses a timer that pulses approximately every 100 milliseconds. This means that the turn-on time and turn-off time are about 50ms each. Modifying the value of the capacitor allows us to adjust these durations.

These generated pulses are directed to a decade binary counter. What the counter does is count the pulses received at its clock input and in response raise the corresponding output pin to a high state. For example, if the pulse count is 3, the Q2 pin on the counter goes high; if it is 5, the Q4 pin goes high. A spike occurs every 100 ms, incrementing the counter memory by 1, which adjusts the output accordingly.

In this setup, Q0, Q2, Q4 are connected to the base of one transistor while Q5, Q7, Q9 are connected to the base of the other transistor. The first transistor controls a pair of red LEDs, and the second transistor controls a set of blue LEDs.

As mentioned earlier, the output of the counter is incremented by 1 every 100 milliseconds until it overflows. After overflow is reached, the counter resets and restarts counting from zero.

The red LED pair is controlled by Q0, Q2, and Q4, and lights up for 100ms, 3 times in total, as follows:

Q0—LED on for 100ms

Q1—LED off for 100ms

Q2—LED lights up for 100ms

Q3—LED off for 100ms

Q4—LED lights up for 100ms

On the next clock cycle, Q5 will go high and all other outputs will go low. Q5, Q7, Q9 are configured to control the pair of blue LEDs so that the blue LEDs light up 3 times for 100ms each, just like the red LEDs.

So we get a pair of red LEDs that blink three times, followed by a pair of blue LEDs that also blink three times. This alternating pattern between the two pairs creates the effect of police lights.