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UNVERIFIED. This layout is drawn and checked in Copper Bottom - the copper agrees with the netlist below, and the checks come back clean. It has not been built on the bench. Nobody has heard it. Build it once, fix whatever fought back, and this banner comes off.

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, 20 by 18 stripboard. Eighteen orange copper strips lettered a to r run left to right with twenty columns numbered above them. A pale rectangle marked IC1 CD4024 sits toward the left. Ten outlined rectangles standing upright are the resistors R1 to R10, a small outlined box is the ceramic capacitor C1 and a pink circle the electrolytic C2. Gray X marks show the cut strips and two dark blue link wires stand vertically. Holes carrying wires off the board are labeled in the margins: V plus, GND, CLK IN, MR PAD, seven reading SW1 A to SW7 A, BUS, VOL T, VOL W, VOL G, OUT T and OUT S. 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, each 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.

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, 18 strips × 20 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 on MR_PAD for a retrigger - optional

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 here is a retrigger
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.

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.
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.
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 4024 octave divider, the same idea as the Dead-Bug Grub. Layout drawn by Onion Madder in Copper Bottom.