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Grub Divider

Seven octaves down a CD4024, switched into one bus, drawn in Copper Bottom · By Onion Madder · Mess O' Pedals

The Dead-Bug Grub, soldered and given switches. A CD4024 is seven flip-flops in a chain: feed a square wave into one end and every output along it is another octave down. This board brings all seven out through weighted resistors onto one bus, each on its own switch - so you are not choosing an octave, you are mixing them, and the weighting means the low ones sit under the high ones instead of burying them.

The Grub Divider layout drawn as a stripboard diagram, titled Grub Divider, 17 by 9 stripboard. Nine orange copper strips lettered a to i run left to right with seventeen columns numbered above them. A pale rectangle marked IC1 CD4024 sits right of center across strips b to h, its top end over strip a. Seven outlined resistors R1 to R7 lie along the strips either side of the chip, four to its left and three to its right, each with a gray X cut under it; R8 and R9 stand across the strips at the far left, R10 lies along the top strip at the right, a small outlined box on strip b is the ceramic capacitor C1 and a pink circle on the top strip at the left is the electrolytic C2. Two dark blue link wires stand vertically, a short one left of the chip and a long one down the right edge. Holes carrying wires off the board are labeled in the margins: BUS, VOL T, VOL W, CLK IN, MR PAD, SW7 A to SW4 A and GND down the left; OUT T, V plus, OUT S, SW1 A to SW3 A and VOL G down the right. Around the board the panel parts are drawn with a colored wire to each hole: eight toggle switches, a DC jack, two quarter-inch jacks and the volume pot. A parts list and an off-the-board table run underneath and a credit line reads Made with Copper Bottom. Below the front view 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 off-board 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. The file itself is below. The lower drawing is the solder side, mirrored - the side you actually work on.
The 9 by 17 board wired up loose on a dark desk mat, not boxed. The small piece of stripboard sits in the middle with the CD4024 standing in its center, blue resistors lying along the strips either side of the chip, a small electrolytic capacitor at its top edge, a yellow ceramic capacitor and two wire links, one blue and one green. A bundle of white wires runs from the board down and to the right to seven blue miniature toggle switches with chrome levers, lying loose, and up to a narrow offcut of stripboard at the upper right where the white wires gather. Blue, yellow and green wires run down to a pot with no knob at the lower left. A right-angle power plug sits in a panel DC jack at the left on orange and black wires, black cables are plugged into a panel jack at the lower left and an inline jack at the upper right, and an LED on red and black leads is lit at the top left.
Mine, built and working on this layout, still on flying leads: the seven octave switches at the lower right, the volume pot at the lower left and the power plug at the left. The LED is not in the layout file.

What you'll need

tap to expand / collapse
  • 1× CD4024 seven-stage binary counter, 14-pin DIP - spot it: CD4024 printed on top, notch marks pin 1
  • The weighted ladder, one resistor per octave and every value different: 1M, 470K, 220K, 100K, 47K, 22K, 10K. They are what make this a mixer instead of a selector - get one wrong and that octave is too loud or inaudible
  • 2× 100K - the clock and reset pull-downs
  • 1× 1K on the output, 1× 100n (104) across the supply, 1× 10 µF electrolytic to block the DC
  • 1× stripboard, 9 strips × 17 holes or larger, and wire for two links

Off the board

  • 7× SPST switches, one per octave
  • 1× 100K pot, off-board - the volume
  • 1× 9V supply, and something to divide - this makes no sound on its own
  • 2× 1/4″ jack - one for the clock input, one for the output
  • 1× momentary switch between MR_PAD and V+ for a retrigger - optional
  • 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 Grub_Divider.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

Seventeen pads leave the board.

PadGoes to
V+ / GNDThe supply, 3V to 15V
CLK_INThe thing to divide. A square wave from any of the oscillators on this site - the Cicada or the 555 theremin will drive it happily. Held down by its own 100K, so an unplugged input is quiet rather than random
MR_PADMaster reset. Held low by a 100K, so the counter free-runs; touch it high and the chain restarts from the top. A momentary switch between MR_PAD and V+ is a retrigger - the pad is one leg of the switch, and the other leg goes to V+, which is why there is no second pad for it
SW1_A … SW7_A / BUSThe seven octave switches. Each SW pad is one octave arriving through its own weighted resistor; each switch's other side goes to the BUS pad, which is where they all sum. Switch one on and that octave joins the mix
VOL_T / VOL_W / VOL_GVolume pot, all three lugs
OUT_T / OUT_SOutput jack, tip and sleeve

How it works, in one breath

A binary counter counts edges. The first flip-flop changes state on every second input edge, which is a square wave at half the frequency - an octave down. The second halves that again, and so on down the chain, so seven outputs are seven octaves below whatever you feed in, each an exact division rather than an approximation.

What makes this musical rather than a lab instrument is the weighting. All seven arrive at one strip through resistors an octave apart in value - 1M down to 10K - so the higher divisions come in quietly and the low ones come in strong. Turn them on together and you get one fat note with its own subharmonics under it rather than seven squares fighting. That shared strip is the mixer; there is no chip doing it.

Three pins on this chip go nowhere and that is correct. Pins 8, 10 and 13 of a CD4024 are no-connects. Copper Bottom knows the chip now, so its checks leave those three alone and this board reads clean - if you open the file in an older copy of the editor it will call them orphans, and that is the old copy, not the board.

Built, and heard

Built on the bench in September 2026, straight off the first drawing of this board - 18 strips by 20 holes, kept here as Grub_Divider_v1.json - and it works. The 9 by 17 file above is the same circuit on less copper, every net checked against the built board, and I have built that one too: it works. In the photo of the first board below, every off-board part is still on flying leads: the seven octave switches, the volume pot, a 9V battery and the cable out to a practice amp. The lit LED is just a power indicator sitting between V+ and GND so you can see it is on - it is not in the layout file, the pad table above does not describe it, and I did not even solder it. I boxed one in a 125B stood on end, drilled from the jacks-on-top template below, and it sold as the Sub Octave Grub.

It wants a strong signal, and a gain stage in front of it is the biggest improvement I have found. I fed the Hive into a dead-bug Hornet I had already built and wired the Hornet's output straight into the input, and it sounds amazing. Grubworks puts a preamp on the board for exactly that, with an Opto Duet and an Atari Punk Console in front of it.

The finished board on a dark desk, wired but not boxed. A small rectangle of orange stripboard sits in the middle with the CD4024, a row of resistors, one black electrolytic capacitor and two blue link wires. Seven small toggle switches with red bodies hang off the board on white leads, one to the left, three lying along the bottom of the frame and three standing to the upper right beside a volume pot on blue, yellow and green wires. A green 9V battery sits behind the board on red and black leads, a black cable runs from the board up to a purple practice amp lettered LeoJaymz at the top right, and a lit LED on red and black leads lies at the right. A pink keyboard sits behind.
The first 18 by 20 layout, built and working, September 2026. Everything off the board is still on flying leads: the seven octave switches, the volume pot, the 9V, the cable out to the amp, and an LED across V+ and GND so you can see it is on - not in the layout file, and not even soldered.
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.
The seven octave switches run down the right in pitch order, 11 mm apart, with the clock input on the face rather than a wall.
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.
The jacks-on-top sheet is the one I drilled, for the Sub Octave Grub; nobody has drilled the face-only 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 4024 octave divider, the same idea as the Dead-Bug Grub. Layout drawn by Onion Madder in Copper Bottom.