Ambulance Lights

Emergency vehicles have a very distinctive visual signature — a rapid, alternating flash of red and blue lights that instantly grabs attention. With just two LEDs, a Raspberry Pi and Pi4J we can recreate that effect on a breadboard.

This project builds directly on the Blink LED example. Instead of a single LED going on and off, we alternate two LEDs so that when one is on, the other is off.

Source code: projects/ambulance/Ambulance.java

What You Will Learn

• How to control multiple GPIO pins from Java with Pi4J
• How to alternate outputs to create a "flashing" effect
• How timing changes the perceived intensity of the flash
• How to organize a small Pi4J program with more than one LED

Components

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

Wiring

1. Connect the anode (longer leg) of the red LED to a GPIO pin through a 220Ω resistor.
2. Connect the anode of the blue LED to another GPIO pin through a 220Ω resistor.
3. Connect both cathodes (shorter legs) to any GND pin on the Pi.
4. Double-check the polarity before powering the Pi.

How It Works

The program configures two GPIO pins as digital outputs, one for each LED. Inside a loop it turns the red LED on and the blue LED off, waits a short delay, then flips them. Repeating this cycle produces the alternating flash you see on real ambulances.

Shorter delays give a nervous, urgent flash. Longer delays feel calmer and closer to a warning beacon. Play with the timing until it feels right.

Possible Enhancements

• Add a small buzzer for a siren sound
• Add a physical button to start and stop the flashing
• Use PWM to fade between the two lights instead of a hard switch
• Add extra LEDs on each side to build a full light bar

Why It Matters

This is a tiny project, but it is the first step toward more expressive lighting patterns: police cars, tow trucks, fire engines, disco lights. Any effect that alternates between two states is essentially this program with different colors and timings.