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UNVERIFIED. Drawn and checked in Copper Bottom, not built. Both halves are circuits I have built: the APC many times on Paul In The Lab's values, and the Grub half is my built Grub Divider board hole for hole. What nobody has done yet is solder them onto one board and hear whether two 555s on the same supply change how the counter counts.

APC Grub

An Atari Punk Console into seven octaves of divider, on one board · By Onion Madder · Mess O' Pedals

An Atari Punk Console into the Grub Divider is the patch I like best: it goes robotic and chirpy, and which of those depends on how the switches are flipped. This board puts the two together. Two 555s make the APC, a CD4024 divides it into seven octaves down, and seven switches pick which octaves sit in the mix. A MODE toggle hands the divider to an EXT IN jack instead and stops the APC dead, so the Grub still works on anything else you feed it.

The APC Grub layout drawn as a stripboard diagram, titled APC Grub, 22 by 27 stripboard. Twenty-seven orange copper strips lettered a to aa run left to right with twenty-two columns numbered above them. In the top third two pale rectangles marked IC2 NE555 and IC3 NE555 sit side by side across strips c to f, with gray X cuts between and under them, small outlined resistors R11, R12 and R13, small ceramic capacitors C3, C4, C6 and C7, pink round electrolytics C5 and C8, and dark blue wire links standing between the strips, two of them running down from the top strips past the chips to the strips below. The lower two thirds are the Grub: a tall rectangle marked IC1 CD4024 in the middle across strips n to t, seven outlined resistors R1 to R7 standing either side of it, R8, R9 and R10, the ceramic C1 and the electrolytic C2, and a column of cuts near the bottom. Holes carrying wires off the board are labeled on both margins, among them TEMPO A, TEMPO W, MODE V, MODE G, RST 1, RST 2, CV A, CLK IN and MR PAD on the left and WIDTH V, WIDTH W, CV B, APC OUT, V plus, GND and the switch pads on the right. Around the board the panel parts are drawn with a colored wire to each hole: three pots, two toggles labeled DPDT pole A and pole B, eight SPST toggles, two quarter-inch jacks and a DC 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 three chips as dashed outlines 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 Copper Bottom draws it: the component side on top, then the same board from the solder side with the columns running the other way. The APC is the top nine strips and the Grub is everything under them. The mode toggle is one DPDT, drawn as its two poles, SW9 and SW10, because the editor has no DPDT part.

What you'll need

tap to expand / collapse

Thirty-six parts on the board, counting fifteen wire links, and fourteen off it. The Grub half is exactly the Grub Divider's parts, with the same reference numbers.

  • 2× NE555 timer, 8-pin DIP (IC2, IC3) - spot it: NE555 or just 555 printed on top, a notch or a dot at pin 1. IC2 is the oscillator, IC3 the one-shot it triggers. Sockets are worth it
  • 1× CD4024 seven-stage binary counter, 14-pin DIP (IC1) - spot it: CD4024 printed on top, notch marks pin 1
  • The weighted ladder, one resistor per octave and every value different (R1 to R7): 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 resistor (R8, R9) - spot it: bands brown-black-yellow. The clock and reset pull-downs. R8 is what the APC lands on
  • 4× 1K resistor (R10 to R13) - spot it: bands brown-black-red. R10 is the Grub's output. R11 is the APC oscillator's 1K, Paul's value. R12 and R13 are the stops, one in series with each 470K pot, so a knob turned to the end never puts a 555's pin 7 straight onto the supply
  • 1× 10nF ceramic (C3) - spot it: printed 103. The oscillator's timing cap
  • 4× 100nF ceramic (C1, C4, C6, C7) - spot it: printed 104. C4 is the one-shot's timing cap; the other three sit across the supply, one by each chip
  • 2× 10 µF electrolytic (C2, C5) - spot it: a small can, stripe on the minus leg. C5 couples the APC into the divider and C2 blocks the DC on the way out
  • 1× 100 µF electrolytic (C8) - across the supply, for the current two 555s pull every time they switch. Stripe to ground
  • 15× wire links (J1 to J15) - offcuts of component leg. J15 runs under IC3, down the cut column, so it goes in before the chip or its socket
  • 1× stripboard, 27 strips × 22 holes or larger

Off the board

  • 2× 470K pot - TEMPO and WIDTH, Paul's values. Each one wired as a variable resistor: one outer lug and the wiper, the third lug left empty. Their 1K stops are on the board
  • 1× B100K linear pot - VOLUME, all three lugs
  • 1× DPDT toggle, on-on - MODE. One pole picks what the divider hears, the other runs or stops the APC
  • 7× SPST switches, one per octave
  • 2× 1/4″ jack - EXT IN and the output
  • 1× DC jack, 9 V, or a battery snap
  • 1× momentary switch between MR_PAD and V+ for a retrigger - optional, the same as on the Grub
  • An SPST toggle for power, in the positive supply lead between the DC jack or battery and the board's V+ 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 every layout on this shelf, the build document for this one is the file itself: ↓ Download Apc_Grub.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.

Two boards in one. Strips a and b are V+ and ground for the APC, and the two 555s stand side by side under them. Strips g, h and i carry the joins the chips cannot make on their own strips: the oscillator's timing node, the clock from one 555 to the other, and the output on its way to C5. Everything from strip j down is the Grub Divider as I built it, not moved by a hole, and J14 and J15 are the only copper joining the two: one for V+, one for ground.

The netlist

Quoted verbatim from the layout file, and emitted from the copper rather than typed beside it - 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 doing while you stare at it. The APC is OSC_TIM, OSC_DIS, CLOCK and SHOT_TIM; everything from CLK_IN down is the Grub.

The off-board wiring

Twenty-eight pads leave the board: three knobs, the mode toggle, seven octave switches, two jacks and the supply, plus two pads you can leave empty.

PadGoes to
V+ / GNDThe supply, through the power toggle. DC jack positive to the toggle and the toggle to V+; negative to GND, which is also both jack sleeves
TEMPO_A / TEMPO_WThe TEMPO pot, a variable resistor: one outer lug to TEMPO_A, the wiper to TEMPO_W, the third lug empty. TEMPO_A reaches V+ through R12, the stop
WIDTH_V / WIDTH_WThe WIDTH pot, the same way round: one outer lug to WIDTH_V, which is V+, the wiper to WIDTH_W, which reaches the one-shot through R13
APC_OUT / CLK_INMODE, the first pole. Common to CLK_IN. One throw to APC_OUT, the APC after C5; the other to the EXT IN jack's tip. With nothing plugged into EXT IN the divider's input still sits on R8 to ground, so it never floats
RST_1 / RST_2 / MODE_V / MODE_GMODE, the second pole. Its common goes to both RST pads, pin 4 of each 555. The throw on the same side as APC_OUT goes to MODE_V and the other to MODE_G. So when the divider is listening to the APC the 555s run, and when it is listening to EXT IN they are held in reset and make nothing, not even a whine on the supply
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
VOL_T / VOL_W / VOL_GVolume pot, all three lugs
OUT_T / OUT_SOutput jack, tip and sleeve
MR_PADThe Grub's master reset, held low by R9. A momentary switch between MR_PAD and V+ is a retrigger, or leave it empty
CV_A / CV_BPin 5 of each 555, left open as Paul has them. Leave them empty, or a 100K from a CV jack tip to bend the oscillator (CV_A) or the one-shot (CV_B) - untested

How it works, in one breath

The APC is two 555s. IC2 runs free, a square wave whose speed is the TEMPO knob. Every time it falls it triggers IC3, a one-shot that puts out one pulse as long as the WIDTH knob says. When the pulse is shorter than the gap between triggers you hear the oscillator; when it is longer, IC3 is still busy when the next trigger arrives and ignores it, so the pitch jumps down in steps instead of sliding. That stepping is the APC's whole sound.

The CD4024 counts edges. Its first output changes on every second edge, an octave down; each output after it halves that again, seven octaves in all, and the weighted resistors bring them into one bus with the low ones strongest. So every step the APC takes, every octave you have switched on takes it too, lower down. The APC reaches the counter through C5, as it does on my bench: the cap takes the DC off the pulses, so what the counter sees depends on how wide they are as well as how often they come.

Three pins on the CD4024 go nowhere and that is correct. Pins 8, 10 and 13 are no-connects, and Copper Bottom's checks leave them alone. Pin 5 of each 555 is the CV pad and may be left open; the datasheet's 10nF to ground is only needed on a noisy supply.

Things to try

None of these have been tried on this board, because this board has not been built.

  • Leave MODE on the APC and play the switches. That is the patch this board was drawn for.
  • EXT IN from another oscillator - the Cicada or the 555 theremin - is the Grub on its own, with the APC silent.
  • An LFO into CV_A through 100K, the Dual-Wave LFO say, makes the APC wander and the whole octave stack with it.
  • Jumper an SW pad to MR_PAD for odd divisions and looping patterns, the Grub's own trick.

The Atari Punk Console is Forrest Mims' Stepped Tone Generator. The part values on the APC half are Paul Stevenson's, from his two-555 Atari Punk Console layout on Paul In The Lab, which I have built many times; the 1K stops and the decoupling are mine. The divider is my Grub Divider, after the classic 4024 octave divider. The layout and the mode switching are mine, drawn in Copper Bottom, and so is anything wrong with them.