Mosquito

The Atari Punk Console on an NE556, soldered down · Ten strips by sixteen holes · By Onion Madder · Mess O' Pedals

The Dead-Bug Mosquito is the one bug in the series that never got a permanent home - the Hive, Cicada, Grub, Dragonfly and Hornet all made it onto stripboard, and the noise box that started the whole thing did not. This is it: the same NE556, the same two 10n caps and two 1K resistors, the same pitch and shape pots, on ten strips. Timer A runs free, its square wave triggers timer B, and timer B's one-shot is the sound. The output leaves through a 10 µF cap to a volume pot. Nothing added, nothing taken away; the dead-bug page's extras - the CV inputs, the sync out - get an empty pad each, so they can be added without a redraw.

The Mosquito layout drawn as a stripboard diagram, titled Mosquito, 16 by 10 stripboard. Ten orange copper strips lettered a to j run left to right with sixteen columns numbered above them. A pale rectangle marked IC1 NE556 sits across strips b to h in the middle, with seven gray marks in the column beneath it where the strips are cut. A small outlined resistor R1 stands on the top strip left of the chip; R2 stands to the right of the chip between strips f and i. Two green boxes are the ceramic timing caps C1 and C2, one left of the chip reaching to the bottom strip, one right; a taller green box C3 spans from the top strip down to strip h on the left; a pink circle C4 is the electrolytic right of the chip. Dark blue link wires run up and down at the left, the right and above the chip. Holes carrying wires off the board are labeled in the margins: 9V, PITCH_A, PITCH_W, CV_A and GND down the left, SHAPE_W, CV_B, VOL_T, SYNC, SHAPE_A and GND_JACK down the right. Beside the board on the left a toggle switch, a pot and a DC jack are drawn with wires to their pads; on the right two more pots and a quarter-inch jack. A parts list runs underneath and a credit line reads Made with Copper Bottom. 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 cuts as X marks, the chip as a dashed outline with pin 1 boxed and the pads labeled on the margin they now sit nearest. — The board as the layout file draws it. Every part, link, cut and off-board pad in one picture, and the panel parts beside it with a wire to every hole they land in. The file itself is below. The lower drawing is the solder side, mirrored - the side you actually work on.

What you'll need

tap to expand / collapse

1× NE556 dual timer, 14-pin DIP - spot it: NE556 on top, not 555; a notch or dot marks pin 1. Two 555s in one package, which is the whole trick of the circuit
2× 1K (brown-black-red, R1 and R2) - R1 from the supply to pin 1, so the pitch pot at zero cannot short the timer's output to its own timing input; R2 does the same job for the shape pot. R1 stands up
2× 10n ceramic (103, C1 and C2) - the timing caps, one per timer. C1 lies from the left of the chip down to the ground strip, C2 from the right
1× 100n ceramic (104, C3) - supply decoupling, from the top strip down to the chip's ground pin. A long one; leave its leads long
1× 10 µF electrolytic (C4) - the output DC blocker. Spot it: stripe marks the negative leg. Its plus goes on pin 9's strip; it stands up
Stripboard, 10 strips × 16 holes or larger, and solid wire for eight short links

Off the board

2× 1M pots - pitch and shape. Spot it: B1M is the linear one. Wired as variable resistors: the wiper and one outer lug, the third lug left empty. A 500K for shape tightens its range and is fine
1× 10K pot, the volume - spot it: B10K. Wired as a divider: all three lugs. Lug 3 to VOL_T, lug 1 to GND_JACK, wiper to the jack
1× 1/4″ jack for the output - or a small 8 Ω speaker straight off the volume wiper, the way the dead-bug build plays
1× SPST toggle for power, in the positive leg between the DC jack and the 9V pad
1× DC jack or 9V battery snap - a 9V battery, or at least two vape cells in series
An upright 125B - the drill template further down

The layout file is the guide

Like the 555 theremin and the Opto Duet, the build document for this one is the file itself: ↓ Download Mosquito.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.

Strip i is the trigger bus. Timer A's output leaves pin 5 on the left of the chip and timer B's trigger is pin 8 on the right, and no single strip joins them - so a link takes OUT A down to strip i, the strip runs under the chip, and a second link brings it up to pin 8. The SYNC pad sits on that strip: it is the raw oscillator square, the clock out the dead-bug page describes, through a 1K if you use it. Two cuts on the right end of strips h and i make room for the volume and shape pads.

The netlist

Quoted verbatim from the layout file. It was written from the board, so checking the board against it can only pass - what it is for is carrying the circuit somewhere else, and telling you what each strip is supposed to be doing while you stare at it.

# Mosquito - written from the board # 10 strips of 16 holes, 14 parts, 1 chip, 9 cuts # # The Dead-Bug Mosquito soldered down: an NE556 as the Atari Punk Console. # Timer A runs free - R1 from V+ to DIS, the pitch pot from DIS to THR/TRG, # C1 to ground - and its output triggers timer B down the bus strip. Timer B # is the one-shot: the shape pot and R2 from V+ set its width, C2 to ground. # OUT B leaves through C4 to the volume pot. Both resets are held high. # CV_A, CV_B and SYNC are pads for the dead-bug page's extras; leave them empty. V+: @9V J5.A J5.B J6.A J6.B J7.A J7.B R1.A R2.A C3.A IC1.14 IC1.4 IC1.10 GND: @GND J8.A J8.B C1.B C2.B C3.B IC1.7 @GND_JACK DIS_A: IC1.1 R1.B @PITCH_A TIME_A: IC1.2 J1.A J1.B C1.A IC1.6 @PITCH_W CV_A: IC1.3 @CV_A OUT_A: IC1.5 J3.A J3.B J4.A J4.B IC1.8 @SYNC TIME_B: IC1.13 J2.A J2.B C2.A IC1.12 @SHAPE_W CV_B: IC1.11 @CV_B SHAPE_R: R2.B @SHAPE_A OUT_B: IC1.9 C4.A VOL: C4.B @VOL_T

The off-board wiring

Eleven pads leave the board. Three of them are for extras and stay empty on the base build.

Pad	Goes to
9V / GND	The supply. 9V through the power toggle from the DC jack or battery snap; GND to the jack's sleeve or the snap's black lead
PITCH_A / PITCH_W	The pitch pot, as a variable resistor: one outer lug to PITCH_A, the wiper to PITCH_W, the third lug empty. Which outer lug decides which way the knob turns; swap them if it feels backwards
SHAPE_A / SHAPE_W	The shape pot, the same way: one outer lug to SHAPE_A, the wiper to SHAPE_W, the third lug empty
VOL_T	The volume pot, lug 3 - the top of the divider. The output arrives here through C4
GND_JACK	The volume pot's lug 1 and the output jack's sleeve. The wiper goes straight to the jack tip and never touches the board
CV_A / CV_B	Empty. Pins 3 and 11, the control-voltage inputs. The dead-bug page's CV mod is a 100K from a jack tip to one of these; a 10n from either to ground is the other thing they are sometimes given
SYNC	Empty. Timer A's raw square at the pitch rate - a 1K to a jack tip makes it the clock out the dead-bug page describes

Don't eyeball the holes. There is a 1:1 drilling template for the 125B - the box drawn unfolded, so you wrap the sheet around it and every hole lands by folding instead of by measuring. Face plus four walls, true-size circles with a punch dot in the middle. The walls are blank; everything is on the face.
↓ Same box, jacks on top (PDF)
The second sheet keeps every control where this one has it and moves the jacks - power and audio - to the top wall, so the cables leave upward. Two ways to drill one box; pick one.
Drawn for the layout file's parts and nothing else: pitch, shape and volume down the left, the power toggle on the right, DC and the output jack along the bottom. Nobody has drilled this one yet.
Print at 100% / “Actual size”, never “Fit to page” - check the bar measures exactly 4″ before you touch a drill. The face is 66 by 121 mm but only 42 mm of it is drillable once the lid lip is clear, which is why everything sits in a column.

How it works, in one breath

Two timers, one chasing the other. Timer A is an astable: R1 and the pitch pot charge C1 toward two thirds of the supply, the timer flips and discharges it back to a third, and round it goes at a rate the pitch pot sets - a square wave on pin 5. That square goes down the bus strip to pin 8, timer B's trigger. Timer B is a monostable: every time the trigger falls it puts out one pulse whose width is R2 plus the shape pot charging C2, and then it waits for the next fall. When the pulse is shorter than the pitch period you hear the pitch; when it is longer, timer B misses triggers and you hear the divisions and the beating between them, which is the Atari Punk Console's whole personality. C4 takes the DC off pin 9 and the volume pot hands what is left to the jack.

The 1Ks are not optional. With a pot from a timer's discharge pin to its threshold, zero ohms would tie the output straight to the timing cap and the timer would stop. R1 and R2 are the floor under the knob, which is why each pot is wired as a two-lug variable resistor and not a divider - the same rule every pitch pot on this site follows.

Things to try

CV in. A 100K from a jack tip to CV_A bends the pitch with a voltage; the same into CV_B bends the shape. Sleeve to ground. The dead-bug page has the whole mod
Sync out. A 1K from SYNC to a jack tip is timer A's clock, to run the Grub or the Firefly off this box
A second one-shot. The dead-bug page's NE555 voice 2 hangs off the same trigger; SYNC is that node, so it wires up from the pad
Bigger timing caps (47n, 100n) push both timers down into clicks and rhythms; smaller ones (1n) push them up into whistles

Circuit is Forrest Mims's Stepped Tone Generator, the Atari Punk Console, as the Dead-Bug Mosquito builds it. The layout is Onion Madder's, drawn in Copper Bottom.