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UNVERIFIED. This layout is drawn and checked in Copper Bottom - the copper agrees with the netlist below and the checker has nothing to report - but it is not built yet. The pitches and times on this page are the arithmetic of the 555, not a measurement. Build it once, fix whatever fought back, and this banner comes off.

Siren

A 90s cop-car siren · Two 555s on nine strips · By Onion Madder · Mess O' Pedals

Hold the button and the pitch winds up like a motor spinning; let go and it coasts back down. Tap it quick and you get the woop. Flip the wail switch and a slow second 555 presses the button for you, up and down for as long as it is on. Two 555s, one transistor and a handful of parts on a 9 by 21 board, with a line out for an amp or a synth.

The Siren layout drawn as a stripboard diagram, titled Siren, 21 by 9 stripboard. Nine orange copper strips lettered a to i run left to right with twenty-one columns numbered above them. Two pale rectangles marked IC1 NE555 and IC2 NE555 sit staggered: IC2 low on the left across strips e to h, IC1 high on the right across strips b to e, and each has a short dark blue link running diagonally under it. Dark blue links run straight down in several columns, one along the far left edge from strip a to strip h. Every resistor stands up, drawn as a small upright label: R3 and R8 and R9 near IC2, R1 and R2 right of IC1, and R4, R5, R6 and R7 in a cluster below and right of IC1 around the transistor Q1, drawn as a half circle with its legs marked C, B and E. The electrolytics C3, C4, C5 and C7 are pink circles, the ceramics C1, C2 and C6 small green boxes, and the diode D1 stands at the bottom of the left edge. Pads labeled plus 9V, GND, OUT and WAIL_A leave the left edge and BTN_A, WAIL_B and BTN_B the right. Beside the board the panel parts are drawn with a wire to each pad: the DC jack, the power switch SW1, the output jack JK1 and the wail switch SW2 on the left, and the woop button BTN1, normally open, on the right. Below it the same board is drawn again from the solder side, mirrored, with the column numbers running right to left, every solder point as a dot, the cuts as X marks and each chip as an outline with pin 1 boxed. A parts list runs underneath, then an Off the board block listing where each panel part lands.
The board as the layout file draws it, with the panel 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.

What you'll need

tap to expand / collapse
  • 2× NE555 timer, 8-pin DIP (IC1, IC2) - spot it: NE555 on top, a notch or a dot at pin 1. IC1 has to be a bipolar NE555: the pitch bend leans on the 5K divider inside it at pin 5, and a CMOS 7555 or TLC555 will barely bend. IC2, the slow one, can be either
  • 1× 2N3904 NPN transistor (Q1) - spot it: a small black TO-92 with one flat face, 2N3904 printed on the flat. Match its legs to the C, B and E the drawing marks
  • 1× 1N4148 diode (D1) - spot it: a little glass bead with a black band. The band goes toward the bottom strip, away from IC2
  • 3× 10K resistor (R1, R5, R8) - spot it: bands brown-black-orange
  • 2× 2.2K resistor (R2, R7) - spot it: red-red-red. R7 sets how high the pitch goes
  • 1× 1K resistor (R3) - spot it: brown-black-red
  • 1× 4.7K resistor (R4) - spot it: yellow-violet-red. How fast the button spins it up
  • 1× 22K resistor (R6) - spot it: red-red-orange
  • 1× 220K resistor (R9) - spot it: red-red-yellow. With C5 it sets the wail speed
  • 1× 150n capacitor (C1) - spot it: 154. The tone's timing cap, film or ceramic
  • 2× 10n ceramic (C2, C6) - spot it: 103. One on each control pin
  • 1× 47 µF electrolytic (C4) - spot it: a can with a stripe down the negative side. This is the "motor"
  • 1× 22 µF electrolytic (C5) - the wail's timing cap
  • 1× 10 µF electrolytic (C3) - the output cap
  • 1× 100 µF electrolytic (C7) - the biggest can, across the supply
  • Stripboard, 9 strips × 21 holes or larger, and solid wire for ten links. Two of them run diagonally under the chips, one under each, joining pin 2 to pin 6, so lay those before the chips go in. Every resistor stands up

Off the board

  • 1× 9V DC jack, or a 9V battery and snap - spot it: on a battery snap, red lead plus, black lead minus
  • 1× SPST toggle, the power switch, in the positive lead between the supply and the +9V pad
  • 1× momentary pushbutton, normally open - the woop button
  • 1× SPST toggle - the wail switch
  • 1× 1/4 in mono jack - the output

The layout file is the guide

Like the rest of the stripboard shelf, the build document for this one is the file itself: ↓ Download Siren.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 two chips sit staggered, IC2 low on the left and IC1 high on the right, and share strip e: IC2's pin 8 and IC1's pin 4 both want the supply, so one strip between them does both jobs. That is most of why the board is 9 by 21.

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.

The off-board wiring

Seven pads leave the board.

PadGoes to
+9VThe power switch; the switch's other side to the DC jack's center pin, or the battery snap's red lead
GNDThe DC jack's sleeve or the battery snap's black lead, and the output jack's sleeve
OUTThe output jack's tip
BTN_AOne lug of the woop button
BTN_BThe other lug of the woop button
WAIL_AOne lug of the wail switch
WAIL_BThe other lug of the wail switch

How it works, in one breath

IC1 is a plain 555 astable making the tone: R1, R2 and C1 put it at about 650 Hz. Its pin 5 is the top of a divider inside the chip, and pulling that pin down makes the chip run faster. C4 is the motor. The button charges it through R4 in about a fifth of a second, and R6 and R5 drain it over a second or two once you let go. R6 and R5 also feed a slice of C4's voltage to Q1's base, so the fuller C4 is, the harder Q1 pulls pin 5 down and the higher the tone goes. R7 sets that current, which is why any 2N3904 does the same job. With the button held, the arithmetic puts the top somewhere between 1.4 and 1.7 kHz; the bench will say. IC2 is a second astable running slowly, R8, R9 and C5 giving about three and a half seconds up and three and a half down. With the wail switch closed, its output charges C4 through D1 the way the button would, so the siren winds up and coasts down on its own.

Things to try

  • Lower or higher overall. C1 at 220n is lower, 100n is higher
  • A different top note. R7 at 1.8K goes higher when wound up, 2.7K lower
  • A heavier motor. C4 at 100 µF spins up and coasts down slower, and taps need to be a bit longer to woop. A smaller R4 spins up snappier
  • Wail speed. A bigger C5 is slower, a smaller one faster
  • A speaker instead of the line out. A 100 µF cap from pin 3 to an 8 ohm speaker. Untested here
  • Mind the level. The output is the 555's full square wave through C3 and R3, several volts, which is hot for a line input. Start with the amp turned down

The circuit is two datasheet 555 astables and a transistor on the control pin. The layout is Onion Madder's, drawn in Copper Bottom.