I built the siren for my police light
A wailing police siren from two 555 timers: a slow one sweeps the pitch of a fast one up and down into a small speaker.
Free build sheet
The parts, every wire with its length and bend points, a bend guide, both sides of the board and checkboxes to track your progress. Print it or keep it open at the bench.
Open the build sheetWhat you need
12 parts on a perfboard 27 × 17 holes, plus hookup wire.
| Qty | Part | Where to buy |
|---|---|---|
| 1 | Electrolytic Cap10uF C1 | Buy Electrolytic Cap on Amazon |
| 1 | Ceramic Cap10nF C2 | Buy Ceramic Cap on Amazon |
| 1 | Power Input (2-pin) J1 | |
| 1 | Screw Terminal 2P (5.08mm) J2 | |
| 2 | Resistor (axial)10k R1, R3 | Buy Resistor (axial) on Amazon |
| 1 | Resistor (axial)22k R2 | Buy Resistor (axial) on Amazon |
| 2 | Resistor (axial)47k R4, R5 | Buy Resistor (axial) on Amazon |
| 1 | Resistor (axial)100 R6 | Buy Resistor (axial) on Amazon |
| 2 | DIP-8 U1, U2 |
Check every pin against the datasheet of the exact part in your hands before wiring.
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Cut list
24 wires, 631 mm (24.8 in) in total, in the order the build sheet cuts them. Wire numbers match the build sheet. Each length includes 5 mm per end to go through the hole.
| Wire | Colour and net | Length | ||
|---|---|---|---|---|
| 24 | BlackGND Y8 → Y10 | Y8 → Y10 | 15mm | Straight |
| 6 | BlackU2_DISCH T9 → Q9 | T9 → Q9 | 18mm | Straight |
| 12 | BlackU2_TIMING W10 → R9 | W10 → R9 | 25mm | 18mm (90°) |
| 18 | BlackVCC J5 → O8 | J5 → O8 | 30mm | 13mm (90°) |
| 11 | BlueU2_TIMING X9 → X6 | X9 → X6 | 18mm | Straight |
| 17 | BlueVCC C8 → C5 | C8 → C5 | 18mm | Straight |
| 5 | BlueU1_DISCH J9 → K4 | J9 → K4 | 25mm | 18mm (90°) |
| 23 | BlueGND P5 → X7 | P5 → X7 | 40mm | 8mm (90°), 28mm (90°) |
| 22 | GreenGND N7 → O6 | N7 → O6 | 14mm | Straight |
| 4 | GreenU1_DISCH H9 → E9 | H9 → E9 | 18mm | Straight |
| 16 | GreenVCC H6 → D9 | H6 → D9 | 26mm | 10mm (45°), 14mm (45°) |
| 10 | GreenU1_TIMING M5 → E5 | M5 → E5 | 35mm | 8mm (90°), 28mm (90°) |
| 1 | RedSPK V15 → V12 | V15 → V12 | 18mm | Straight |
| 7 | RedU2_DISCH V9 → W4 | V9 → W4 | 25mm | 18mm (90°) |
| 19 | RedVCC P9 → S5 | P9 → S5 | 33mm | 8mm (90°), 18mm (90°) |
| 13 | RedU2_TIMING Y5 → Q5 | Y5 → Q5 | 35mm | 8mm (90°), 28mm (90°) |
| 15 | WhiteVCC I4 → G5 | I4 → G5 | 18mm | 10mm (90°) |
| 9 | WhiteU1_TIMING K10 → F9 | K10 → F9 | 25mm | 18mm (90°) |
| 3 | WhiteTONE T11 → R5 | T11 → R5 | 30mm | 20mm (90°) |
| 21 | WhiteGND C6 → M8 | C6 → M8 | 51mm | 15mm (90°), 41mm (90°) |
| 8 | YellowU1_TIMING L9 → L6 | L9 → L6 | 18mm | Straight |
| 20 | YellowVCC T6 → U4 | T6 → U4 | 18mm | 10mm (90°) |
| 2 | YellowMOD H11 → F5 | H11 → F5 | 30mm | 20mm (90°) |
| 14 | YellowU2_CTRL J15 → S9 | J15 → S9 | 48mm | 28mm (90°) |
About this build
The classic dual 555 siren. One NE555 runs as a slow astable. Its output pushes through a 10k resistor on the control voltage input of a second, fast 555, so the fast tone sweeps up and down instead of holding one pitch.
The fast 555's output drives an 8 ohm speaker on a screw terminal through a 100 ohm resistor, and that's the wail. The slow timer runs on a 10uF electrolytic, the fast one on a 10nF ceramic.
It's two chips, six resistors, two caps and a 2 pin power input, all routed by hand.
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