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Cicada NAND

Four gated voices on one CD4093, drawn in Copper Bottom · By Onion Madder · Mess O' Pedals

The Dead-Bug Cicada soldered down. A CD4093 holds four Schmitt NAND gates, and a NAND with its two inputs tied into a cap and a resistor is an oscillator - the same trick as the 40106, with one extra wire. That extra wire is the point: a NAND only oscillates while its other input is high, so every voice here has a gate as well as a pitch knob. Pull a gate low and that voice stops dead.

The Cicada NAND layout drawn as a stripboard diagram, titled Cicada NAND, 18 by 12 stripboard. Twelve orange copper strips lettered a to l run left to right with eighteen columns numbered above them. A pale rectangle marked IC1 CD4093 sits right of center across strips b to h, with a column of gray X marks through the strips under it and more X marks scattered on the strips either side. Outlined resistors marked R1 to R12 and small green capacitors marked C1 to C9 stand between the strips, one pink round electrolytic C10 sits at the lower left, and five dark blue link wires run between strips. Holes carrying wires off the board are labeled on both margins: V1 WIPER, GND JACK, GND, V2 WIPER, V1 LUG, V1 EN, V2 LUG, V2 EN, OUT and V3 WIPER on the left, V4 WIPER, V4 EN, V4 LUG, V3 EN, V3 LUG and V plus on the right. Beside the board the panel parts are drawn with a wire to every hole they land in: four potentiometers, five SPST toggles, a DC jack and a quarter-inch jack. 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 and the chip as a dashed outline with pin 1 boxed. A parts list follows, then a block headed OFF THE BOARD listing each panel part, what it does and where each of its legs goes.
The board as the layout file draws it. Every part, link, cut and off-board pad in one picture. The file itself is below. The lower drawing is the solder side, mirrored - the side you actually work on.
The 12 by 18 board wired up loose on a dark desk mat, not boxed, with a pink keyboard across the top of the frame. The stripboard sits low in the middle, its strips lettered A to L down the right edge. A black 14-pin chip stands in the center, with four orange box capacitors along the lower half, yellow drop-shaped ceramic capacitors, blue and tan resistors standing on end, red wire links and a small electrolytic capacitor at the lower left. Yellow, green and blue wires run up from the board to four pots with no knobs, three in a row above it and one to the right. A chrome right-angle plug sits in a panel jack at the left, an LED on red and black leads is lit beside it, and a right-angle power plug sits in a panel DC jack at the right. There are no switches anywhere in the picture.
Mine, built and working on this layout, still on flying leads and without any of its switches: the four pitch pots above the board, the output jack at the left and the power plug at the right.

What you'll need

tap to expand / collapse
  • 1× CD4093 quad Schmitt NAND, 14-pin DIP - spot it: CD4093 printed on top, notch marks pin 1
  • 4× ceramic capacitors, one per voice - the ladder here is 102 (1n), 103 (10n), 104 (100n) and 105 (1 µF). Each one sets that voice's register
  • 4× 1K (brown-black-red) - one per pot, in series and not optional: at zero ohms the gate's output ties straight to its own input and the voice dies into a short
  • 4× 1M (brown-black-green) - the gate pull-ups. Each one holds a voice enabled until something pulls it down
  • 4× 10K (brown-black-orange) and 4× 1 µF non-polarized - the mixer, one pair per voice
  • 1× 100n (104) across the supply, and 1× 10 µF electrolytic on the output
  • 1× stripboard, 12 strips × 18 holes or larger, and wire for five links

Off the board

  • 4× 1M pots, off-board, one per voice - the pitch. Spot it: B1M is the linear one
  • 1× 9V supply, or two vape cells in series
  • 1× 1/4″ jack for the output - tip to OUT, sleeve to GND_JACK
  • Something for each gate, if you want gates. A toggle to ground is an on/off per voice, two bare contacts are a touch plate, a photocell is a light-gated voice. The pads work bare too - every voice runs until you pull its gate low
  • An SPST toggle for power, in the positive supply lead between the DC jack or battery and the board's supply pad. Not in the layout file - it is off the board, and every build on this shelf gets one

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 Cicada_NAND.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 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.

The off-board wiring

Sixteen pads leave the board.

PadGoes to
V+ / GNDThe supply. A 4093 is happy anywhere from 3V to 15V, so a 9V battery or a vape pack both work. The 100n sits across the rail on the board
V1_LUG … V4_LUG
V1_WIPER … V4_WIPER		The four pitch pots, two connections each: wiper to WIPER, either outer lug to LUG, and the third lug left bare. A variable resistor, not a divider - the same wiring as every pitch control on this site
V1_EN … V4_ENThe gates, and the reason to build this one rather than a 40106. Each is held high by its own 1M, so the voice runs on its own. Short one to ground and that voice stops. A switch here is an on/off per voice; a pair of contacts is a touch plate; a photocell is a light-gated voice
OUT / GND_JACKJack tip and sleeve. The 10 µF blocks the DC on the way out

I have built this four times

The first layout of this board - 15 strips by 28 holes, kept here as Cicada_NAND_v1.json - has gone together four times now and every one of them worked first try. That is the main thing I can tell you about it as a design: it is not fussy, and it does not care much what you hang off it. The 12 by 18 file above is the same circuit on less than half the copper, every net checked against the built board, and it is built too: wired without any of its switches, and it works.

The finished board on a dark desk mat, wired but not yet boxed. A rectangular strip of perfboard sits in the middle with its solder side up, its rows of holes joined by bright blobs of solder. Four potentiometers with bare knurled shafts and no knobs lie above it on blue, yellow and teal wires, and three toggle switches with blue and red bodies lie below on white and orange wires. A red LED glows at the left on red and black leads, a right-angle DC power plug enters from the lower left, and a quarter-inch jack with a purple instrument cable sits at the right. A pink cat-themed keyboard fills the top of the frame.
The first 15 by 28 layout, built and working, with four pitch pots and the gate switches on flying leads. It carries a few extra bends of my own on top of that layout, so it is not a hole-for-hole copy of either drawing.

It takes extra bends well, too. Every one I have built picked up a few of my own on top of the drawing and the board never minded. The fourth ended up in a floral tin with five knobs and six toggles on the lid, and it is for sale as Garden Variety.

Those bends are not on the layout and they are not going to be, because they are not the kind of thing you can draw. They interact: what any one of them does depends on where the others are sitting, which is why the tin has no knob list either. Build the board, get it running, and then start bridging things and find your own.

There is a solderless version of this exact circuit. The Cicada NAND on a breadboard is this board unrolled onto a breadboard, net for net - all twenty-four of them match the netlist above. It adds one thing this board does not have, a volume knob, wired as a divider off the board between the output cap and the jack - which is worth doing here too. Nobody has built that one yet, so it wears a draft banner; the copper under it is the built board.

How it works, in one breath

A Schmitt NAND behaves like an inverter with a permission slip. Tie a cap from the input to ground and a resistor from the output back to the input and it chases itself: the cap charges until the input crosses the upper threshold, the output flips, the cap drains until it crosses the lower one, and around it goes. The pot is that resistor, so the knob is the pitch and the cap decides the register.

The second input is the difference. It has to be high for the gate to invert at all, so it is a gate in the musical sense - and because each is held up by nothing but a 1M, almost anything pulling it down will silence that voice. Four outputs then go through their own 10K and 1 µF onto one shared strip, which is the whole mixer: four resistors meeting at a point.

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.
Four voices, each a pot with its gate switch beside it, so a row across the face is one voice.
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.
Nobody has drilled this one yet. The hole sizes come from the layout file; where they sit is this format applied to it. Offer the sheet up to the box and check it against your own parts before you make a hole.

Circuit after the classic 4093 oscillator bank - the same idea as the Dead-Bug Cicada, which is where the name comes from. Layout drawn by Onion Madder in Copper Bottom.