Police Lights

A red and blue wig-wag · One 555 on nine strips · By Onion Madder · Mess O' Pedals

One 555 timer, a red LED and a blue one, taking turns about three times a second. There is no second chip and no transistor: the red LED hangs from the timer's output down to ground, the blue one from the supply down to the output, so the output lights red when it goes high and blue when it goes low. They can never be on together. Ten parts on a 9 by 13 board, and a power switch in the supply lead.

The Police Lights layout drawn as a stripboard diagram, titled Police Lights, 13 by 9 stripboard. Nine orange copper strips lettered a to i run left to right with thirteen columns numbered above them. A pale rectangle marked IC1 NE555 sits in the middle across strips c to f, with the strips cut under its center. Five dark blue links run straight down: two at the far left, one beside them, and two right of the chip. The resistors R4 and R3 stand left of the chip and R1 and R2 to its right; the electrolytics C3 at the upper left and C1 at the lower right are pink circles, and the ceramic C2 is a small green box at the right edge. Two red circles mark the LEDs: D2 at the top right and D1 at the bottom, below the chip. Plus 9V and GND leave the right edge and run to a power switch, SW1, and a 9 volt battery snap, BT1, drawn beside the board. Below it the same board is drawn a second time from the solder side, mirrored, with the column numbers running right to left, every solder point as a dark dot, the four cuts as X marks and the chip as an outline with pin 1 boxed. A parts list runs underneath, reading R1 10k, R2 100k, R3 and R4 470, C1 2u2, C2 10n, C3 100u, D1 red, D2 blue, BT1 battery snap 9 V, IC1 NE555 and SW1 toggle switch SPST, then an Off the board block wiring SW1 between the battery's plus and the plus 9V pad, and a credit line reading Made with Copper Bottom. — The board as the layout file draws it, with the power switch and battery snap beside it. Every part, link, cut and off-board pad in one picture. The lower drawing is the solder side, mirrored - the side you actually work on.

The Police Lights built on a small piece of stripboard, lying on a dark bench with wires trailing off it. The 555 sits in the middle of the board with a black electrolytic capacitor standing beside it and a small yellow capacitor near its edge. To the left a 9 V battery lies on its side, its snap leads running up to a small red toggle switch at the top of the picture. To the right two LEDs hang on long red and black leads; one of them is lit and throws a bright glow across the bench. — Built and working, on the bench in October 2026: the board, the battery and its power switch, and the two LEDs.

What you'll need

tap to expand / collapse

1× NE555 timer, 8-pin DIP (IC1) - spot it: NE555 or just 555 on top, a notch or a dot at pin 1. A CMOS 7555 or TLC555 sits in the same holes and works too
1× red LED (D1) and 1× blue LED (D2) - spot it: the long leg is the anode; the short leg, on the flat side of the rim, is the cathode, which the drawing marks. Plain LEDs, not self-flashing ones: those run their own clocks and drift out of step instead of taking turns. Pre-wired LEDs on leads work too, soldered into the same two holes, if the lights are going on a box away from the board
1× 10K resistor (R1) - spot it: bands brown-black-orange
1× 100K resistor (R2) - spot it: brown-black-yellow. With C1 it sets the rate
2× 470 ohm resistor (R3, R4) - spot it: yellow-violet-brown. One for each LED
1× 2.2 µF electrolytic (C1) - spot it: a small can with a stripe down the negative side. The timing cap
1× 100 µF electrolytic (C3) - the bigger can, across the supply
1× 10n ceramic (C2) - spot it: 103. On the control pin, to keep the rate steady
Stripboard, 9 strips × 13 holes or larger, and solid wire for five links

Off the board

1× SPST toggle, the power switch, in the positive lead between the supply and the +9V pad
1× 9V battery and snap - spot it: red lead plus, black lead minus

The layout file is the guide

Like the rest of the stripboard shelf, the build document for this one is the file itself: ↓ Download Police_Lights.json - import it into Copper Bottom and the editor gives you the board picture, the placement walkthrough, the electrical checks and a printable build sheet, all from the same file. No coordinates are written out on this page on purpose: the editor is the viewer, and a number typed twice is a number that can drift.

The netlist

Quoted verbatim from the layout file. It says what each strip is supposed to be doing while you stare at it, and it carries the circuit somewhere else if you want to lay it out your own way.

# Police Lights - a 555 wig-wag, red and blue # One 555 flips red and blue back and forth. Pin 3 high lights red # (pin 3 through R3 and red to ground); pin 3 low lights blue (+9V through blue and R4 into pin 3). # They can never be on together, so it is a clean wig-wag with no extra chips. # About 3 flips a second. Slower: bigger C1. Faster: smaller C1. # Speed knob: a 100k pot in series with R2. # Brighter LEDs: drop R3 and R4 to 330. # Use plain LEDs, not self-flashing ones - those run their own clocks # and drift out of step instead of taking turns. # NE555 or a CMOS 7555 / TLC555 both work. V+: @+9V IC1.8 IC1.4 R1.A C3.A D2.A GND: @GND IC1.1 C1.B C2.B C3.B D1.B DIS: IC1.7 R1.B R2.A THR: IC1.2 IC1.6 R2.B C1.A CV: IC1.5 C2.A OUT: IC1.3 R3.A R4.B RED: R3.B D1.A BLUE: D2.B R4.A

The off-board wiring

Two pads leave the board.

Pad	Goes to
+9V	The power switch; the switch's other side to the battery snap's red lead
GND	The battery snap's black lead

Built, and seen

Built on the bench in October 2026, straight off the file above, running from a 9V battery through a toggle switch, and it looks like police lights.

How it works, in one breath

The 555 is wired as the datasheet's astable: C1 charges through R1 and R2 and discharges through R2, and the output flips each time. That works out at about 3.1 cycles a second, red for about 0.17 of a second and blue for about 0.15. When the output is high, current runs out of pin 3, through R3 and the red LED to ground. When it is low, current runs from the supply through the blue LED and R4 into pin 3. While red is lit, the blue LED has only the gap between the output and the supply across it, about 1.7 volts on an NE555, which is short of what a blue LED needs to light. By the arithmetic, each LED gets roughly 10 to 12 mA.

Things to try

Slower or faster. A bigger C1 slows it down and a smaller one speeds it up: 4.7 µF is about one and a half flips a second
A speed knob. A 100K pot in series with R2, wired as a variable resistor
Brighter. R3 and R4 down to 330 ohms
Other colors. Untested: a low-voltage LED such as a second red in the blue position may glow faintly while the other one is lit, because an NE555's high sits about 1.7 volts under the supply. A 7555 or TLC555 goes all the way up and should keep it dark

The circuit is the 555 astable from the datasheet, with one LED sourced and one sunk from the same output. The layout is Onion Madder's, drawn in Copper Bottom.