# Police Style Strobe Light

This electronic circuit shows the familiar lights which are used on police cars.

To achieve this strobe light effect, two groups of LEDs are used. Each group has three LEDs and they turn on and off alternately. Whenever a group is activated, its LEDs turn on and off three times. LEDs can be red for one group and blue for the other.

## How the Police Style Strobe Light works?

This Police Style Strobe Light circuit uses a 555 timer that works as a clock for the 4017B decade counter. You can change the speed of the clock, changing the values of the resistor and capacitor connected to the timer. Although values of the components allready chosen, work pretty well.

The 4017B decades counter, deliver sequentially at its outputs a high signal level. On the circuit diagram we see that the outputs 0, 2, 4 and 5, 7, 9 are connected to transistors Q2 and Q1, and outputs 1,3,6 and 8 are not.

When the 4017 decade counter activate one of its outputs that is not connected, no LED lights and some time elapses. This time is necessary in order that the LEDs look OFF. Thus, the effect of flashing LEDs (the stroboscopic light effect) is created when each group is enabled.

Blue LEDs are connected to transistor Q2 and red LEDs are connected to transistor Q1.

## List of circuit components for Police Style Strobe Light

• IC1: 555 timer
• Q1 = Q2: 2N2222 bipolar transistor or a similar one
• D1 = D2 = D3 = D4 = D5 = D6 1N4001 diode
• D7 to D18: Red and Blue LEDs
• R1: 1K resistor
• R2: 22K resistor
• R3 to R10: 470 ohm resistors
• C1: 2.2uF Electrolytic capacitor
• C2: 0.01uF capacitor.

The circuit is powered by a 12VDC supply or a car battery (B +).

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