Strobe light controller, using the AVR ATtiny2313 microcontroller. Meant for cars; with front, side and rear warning lights.

Table of contents


On my old car, a Subaru Legacy, I built and installed warning lights on all sides. Never really used them, but it was a fun build. I had a total of 8 LED warning lights, all around the car. The lights on the side was used as side markers when not flashing. I originally used the red break light as the rear warning light, but later replaced it with two self-built warning lights.

Car front, with warning LEDs
Car front, with warning LEDs

I used self-built LED warning lights in the front and rear, while the side lights were regular side markers. When the warning lights were not flashing; the side markers lit continuously at 10% duty cycle. And then the car started the front side markers would fade in, then the rear, it looked kind of cool from the side 🙂

Car back, with warning LEDs
Car back, with warning LEDs

The front warning lights split the patterns between them, so alternating from side to side. While the side and rear lights flashed together. The module was originally designed to use the cars additional break light, that is why the rear output is a bit different from the rest. It has two transistors and gives out 12V, while the rest are open collector.

Kids facinated by side warning LED
Kids facinated by side warning LED

The signal to activate the warning lights came from another microcontroller module I built for the car; a controller for the additional headlights controller for the additional headlights I installed.


Early test

Mounted on car


Controller board, with wires
Controller board, with wires


  1. PD6 - Flash signal (Opto-isolator)


  1. PB0 + Rear LEDs
  2. PB1 - Front LED 1
  3. PB2 - Front LED 2
  4. PB3 - Yellow light 1 (PWM)
  5. PB4 - Yellow light 2 (PWM)

Warning LEDs

Four very simple LED warning lights, with a total of 10 LEDs; 2x2 and 2x3. The yellow LEDs have four chips, making them pretty bright. And with a 40 degree light beam they are quite visible, even more so at a distance. So they make pretty good warning lights. Powered by: 12-13.8V.

LEDs and resistors soldered
LEDs and resistors soldered

By hot-gluing the resistors, LED, wire hole and around lid they can easily be made water-proof. For seven years I had two mounted in front of my old car, getting hammered by with water, snow and salt. Never had any problems with them.

Testing warning LEDs
Testing warning LEDs

Parts I used to build the LED warning lights:

  • 2 × Enclosure, plastic (1551), 60x35x20mm
  • 2 × Enclosure, plastic (1551), 80x35x20mm
  • 10 × LED 10mm clear, Yellow, 2.1V, 80mA, 8lm, 40°
  • 10 × Resistor, metal film, 1W, 150 Ω, 5%
  • 4 × Terminal block, pluggable, 3.5 mm, 2-pin screw female
  • 1 m Wire, stranded, 0.22mm2, Black
  • 4 m Wire, stranded, 0.22mm2, Grey
  • 1 m Wire, stranded, 0.22mm2, White
  • 4 m Wire, stranded, 0.22mm2, Yellow

Source code

Schematic drawing

Strobe light controller schematics
Strobe light controller schematics

Parts list

  • 1 × AVR ATtiny2313-20PU, DIL-20, 20 MHz, 18 I/Os
  • 1 × Capacitor, aluminium electrolytic, 10 µF, 25V
  • 2 × Capacitor, aluminium electrolytic, 47 µF, 25V
  • 1 × Capacitor, ceramic, 1 nF, 100V
  • 1 × Capacitor, metallized polyester foil, 10 nF, (0.01 µF)
  • 1 × DIL socket, 20-pin, 7.62mm
  • 1 × DIL socket, 6-pin, 7.62mm
  • 1 × Enclosure, plastic (1591 FL), 100x50x25mm, flange
  • 1 × Fuse 5x20 mm, 500 mA, fast-acting
  • 1 × Fuse 5x20 mm, 1 A, fast-acting
  • 2 × Fuse holder, wire, 5x20 / 6.3x32mm
  • 1 × Heatsink, 27.3K/W, 19mm, attachable, TO220
  • 1 × Optocoupler, single, CNY17F-3, DIL-6
  • 32 cm2 PCB, stripboard, 100x160mm, 160cm2
  • 1 × Resistor, carbon film, 0.25W, 330 Ω, 5%
  • 7 × Resistor, carbon film, 0.25W, 4.7 kΩ, 5%
  • 1 × Resistor, carbon film, 0.25W, 10 kΩ, 5%
  • 1 × Resistor, metal film, 0.6W, 1 kΩ, 1%
  • 8 × Straight pin header, female, Single row, 2.54mm
  • 9 × Straight pin header, male, Single row, 2.54mm
  • 16 × Terminal block, screw, 2.5 mm
  • 1 × Transistor, NPN, 100 mA, 45V, 0.5W, BC547B
  • 4 × Transistor, NPN, 800 mA, 45V, 0.625W, BC337-25
  • 1 × Transistor, PNP, 800 mA, 45V, 0.625W, BC327-25
  • 1 × Voltage regulator +5V, 2 A, L78S05CV
  • 4 m Wire, stranded, 0.50mm2, Yellow
  • 25 m Wire, stranded, 0.75mm2, Blue