Police Lights

Police cars use a much more aggressive light pattern than a simple back-and-forth. Each side of the light bar usually fires two or three quick strobes before the other side takes over. That double-flash rhythm is instantly recognizable.

In this project we simulate that effect using two LEDs — one red and one blue — controlled from a Raspberry Pi with Pi4J. It is a natural next step after the Ambulance Lights project.

Source code: projects/police/Police.java

What You Will Learn

How to build more complex blinking patterns with nested loops
How to control two LEDs with independent timings
How rhythm and grouping change the visual "personality" of a light
How to keep GPIO code readable when patterns become more elaborate

Components

Raspberry Pi
1 red LED
1 blue LED
2 × 220Ω resistors
Breadboard
Jumper wires

Wiring

Connect the anode of the red LED to a GPIO pin through a 220Ω resistor.
Connect the anode of the blue LED to another GPIO pin through a 220Ω resistor.
Connect both cathodes to any GND pin on the Pi.

How It Works

The program configures two GPIO pins as digital outputs. Instead of a simple alternating flash, each side fires three quick strobes before handing over to the other side. A short delay between the two bursts sells the "police strobe" feel.

The pattern is essentially:

Red strobes three times, very fast.
Short pause.
Blue strobes three times, very fast.
Short pause.
Repeat.

Tweaking the number of strobes and the on/off durations gives you a whole family of related effects.

Possible Enhancements

Add a siren tone with a piezo buzzer
Add more LEDs on each side for a fuller light bar
Randomize the number of strobes per burst for a more chaotic effect
Trigger the pattern with a button press

Why It Matters

Once you can time nested patterns like this, you can drive almost any real-world signal light: fire trucks, tow trucks, road hazard beacons, and construction lights. It is a great exercise in structuring blinking code that goes beyond a single loop.