Opto Wobble

The Opto Duet with an LFO on its pin 5s, and a CV input · By Onion Madder · Mess O' Pedals

The Opto Duet is two 555s coupled by nothing but light: a slow engine ticks, its LED flashes, and the flash bends the voice. This puts my Dual-Wave LFO on the same board and sends its output into pin 5 of either 555, through an on-off-on toggle and a dual 50K pot. Pin 5 is where a 555 keeps its reference voltage, so the LFO wobbles the engine's tempo or the voice's pitch, whichever the toggle picks. A CV jack goes into the engine's pin 5 as well, through 47K. In this box the Duet's two photocell eyes are knobs, tempo and pitch, and the one vactrol inside still carries the engine's flash to the voice.

The Opto Wobble layout drawn as a stripboard diagram, titled Opto Wobble, 23 by 18 stripboard. Eighteen orange copper strips lettered a to r run left to right with twenty-three columns numbered above them. The top nine strips hold the Opto Duet: two pale rectangles marked IC1 NE555 and IC2 NE555 side by side, a diode D1 on the top strip, resistors R1 to R4, pink round electrolytics and small green ceramic capacitors, with dark blue links, one running diagonally under IC1. Strip j is nearly empty, cut once, with a pad marked CV at its left end and a resistor R10 standing from it up to IC1's pin 5 strip. The bottom eight strips hold the Dual-Wave LFO: a pale rectangle marked IC3 NE5532, resistors R6 to R9, capacitors C10 to C12 and more links. Three long links carry ground and the supply between the two halves. Pads are labeled around the edges: plus 12V, GND, LDR_T1, LDR_T2, P5_1, SPK_B, LED_K, LED_A, CV and VR2_3 on the left, VCC, LDR_V1, LDR_P1, LDR_V2, LDR_P2, P5_2, LED2_K, LED2_A, SPK_A, VR2_1, RATE_LED, VR1_3 and VR1_W on the right. Beside the board the panel parts are drawn with a wire to every pad: a power toggle, a DC jack, a quarter-inch line out and a 3.5 mm CV in jack, a red power LED with an off-board 4K7 resistor, the LED and photocell of the vactrol, pots marked 2K and 100K for tempo and pitch, a rate pot, a blend pot, the two gangs of the dual 50K pot, and an on-off-on toggle wired between the blend pot and the two gangs. 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 and where each of its legs goes. — The board as the layout file draws it. The Opto Duet is on strips a to i and the Dual-Wave LFO on k to r, each exactly as its own page has it. Strip j between them carries the CV input and a bridge for the supply. The lower drawing is the solder side, mirrored - the side you actually work on.

What you'll need

tap to expand / collapse

Everything from both boards, plus one resistor and the wobble controls. The part numbers below are this board's; the LFO's parts are renumbered from its own page so nothing collides.

2× NE555 timer, 8-pin DIP (IC1, IC2) - spot it: NE555 printed on top, notch marks pin 1
1× NE5532 dual op-amp, 8-pin DIP (IC3) - the LFO. Spot it: 5532 in the part number, a notch at one end
1× 1N5817 Schottky (D1) - spot it: black body, gray band. Reverse-polarity protection, and it protects the LFO too: it runs from the same rail
2× 47K (yellow-violet-orange) - R6, the LFO's rate floor, and R10, which carries the CV input onto IC1's pin 5
1× 100K (brown-black-yellow) (R9) - the LFO comparator's feedback. It stands on end, across two holes
2× 10K (brown-black-orange) (R7, R8) - the LFO's half-rail divider
2× 1K (brown-black-red) (R1, R3) - one per 555 timing chain
2× 100R (brown-black-brown) (R2, R4) - the output resistors
1× 1 µF film (C10) - the LFO's timing cap. Film, not ceramic
1× 10 µF electrolytic (C1) - the engine's timing cap
1× 47 µF electrolytic (C11) - holds the LFO's half rail still
3× 100 µF electrolytic (C3, C6, C7) - two output couplers and one across the rails. Spot it: the stripe marks the negative leg
4× 100n ceramic (104) (C4, C8, C9, C12) - the voice's timing cap and a decoupling cap beside each chip
2× 10n ceramic (103) (C2, C5) - the pin 5 caps, one per 555. They stay: the LFO and the CV go in beside them
Stripboard, 18 strips × 23 holes or larger, and wire for seventeen links. J15, J16 and J17 are the ones that join the two halves: J15 the grounds, J16 and J17 the supply, by way of strip j

Off the board

1× 2K pot - TEMPO, where the Duet has its tempo eye. Wired as a variable resistor, lug 1 and wiper; lug 3 stays empty
1× 100K pot - PITCH, where the Duet has its pitch eye. Lug 1 and wiper; lug 3 stays empty
1× photocell and 1× LED, sealed face to face in heat-shrink - the vactrol, inside the box. The LED runs bare, no resistor, the same as on the Opto Duet
1× 100K linear pot (B100K) - the LFO rate. Wiper and lug 3; lug 1 stays empty
1× 1K linear pot (B1K) - the LFO blend, all three lugs. Its wiper is what feeds the wobble: triangle at one end of the knob, square at the other
1× dual 50K pot - WOBBLE, one gang per 555. Each gang is wired as a variable resistor, lug 1 and wiper, with nothing in series: see Built, and heard
1× on-off-on toggle - LFO: sends the wobble to the engine, nowhere, or the voice
1× 1/4″ jack - the line out, in place of the speaker
1× 3.5 mm jack - CV in
1× LED and a 4K7 resistor (yellow-violet-red) - the power light, from VCC to ground
1× DC jack, 12V, center-negative, and an SPST toggle for power in the positive lead
An upright 125B - the drill templates are in the rail

The layout file is the guide

Like every layout on this shelf, the build document for this one is the file itself: ↓ Download Opto_Wobble.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, hole for hole. The file was built from the two shipped layout files, not redrawn, and it only exists because every net of both came through intact - the generator refuses to write it otherwise. The editor's four warnings on it are the Opto Duet's own: C1 is a squeeze beside IC1, and R2 and R4 stand on end.

The netlist

Quoted verbatim from the layout file, and emitted from the copper rather than typed beside it. The lines worth finding are IC1_CTRL and IC2_CTRL, the two pin 5 strips, and TRIANGLE and SQUARE, the two ends of the blend knob that feeds the wobble.

# Opto Wobble - written from the board # 18 strips of 23 holes, 39 parts, 3 chips, 19 cuts # # The Opto Duet v2 on strips a to i and the Dual-Wave LFO on k to r, both hole # for hole as shipped. The LFO parts are renumbered: its chip is IC3. J15 joins # the grounds and J16 feeds the LFO from VCC, after D1. The LFO leaves through # the blend pot on VR2_1 and VR2_3, and its wiper comes back through the toggle # and the dual pot on P5_1 or P5_2, pin 5 of either 555. R10 carries the CV # input onto IC1 pin 5. +12V: @+12V D1.A VCC: @VCC C12.A C7.A C8.A C9.A D1.B IC1.4 IC1.8 IC2.4 IC2.8 IC3.8 J16.A J16.B J17.A J17.B J2.A J2.B J3.A J3.B J5.A J5.B J6.A J6.B R1.A R3.A R7.B GND: @GND @LED2_K @LED_K @SPK_B C1.B C11.B C12.B C2.B C4.B C5.B C7.B C8.B C9.B IC1.1 IC2.1 IC3.4 J1.A J1.B J13.A J13.B J15.A J15.B J8.A J8.B J9.A J9.B R8.A LDR_T2: @LDR_T2 C1.A IC1.2 IC1.6 J4.A J4.B LDR_T1: @LDR_T1 IC1.7 R1.B LDR_V2: @LDR_P2 @LDR_V2 C4.A IC2.2 IC2.6 J7.A J7.B LDR_V1: @LDR_P1 @LDR_V1 IC2.7 R3.B IC1_OUT: C3.A IC1.3 IC2_OUT: C6.A IC2.3 IC1_CTRL: @P5_1 C2.A IC1.5 R10.B IC2_CTRL: @P5_2 C5.A IC2.5 LED_A: @LED_A C3.B R2.A LED2_A: @LED2_A C6.B R4.A SPK_A: @SPK_A R2.B R4.B TRIANGLE: @VR2_1 C10.B IC3.1 IC3.5 J12.A J12.B J14.A J14.B R9.A INT_IN: C10.A IC3.2 R6.B SQUARE: @RATE_LED @VR1_3 @VR2_3 IC3.7 R9.B BIAS: C11.A IC3.3 IC3.6 J10.A J10.B J11.A J11.B R7.A R8.B RATE: @VR1_W R6.A CV: @CV R10.A

The off-board wiring

Pad	Goes to
+12V / GND	The supply, 12V center-negative, through the power toggle to +12V. D1 on the board takes it from there, and the LFO runs from the same rail. GND also takes the CV jack's sleeve and the power LED's cathode
VCC	The 4K7, then the power LED's anode
LDR_T1 / LDR_T2	TEMPO, the 2K pot, lug 1 and wiper, where the tempo eye would go
LDR_P1 / LDR_V2	PITCH, the 100K pot, lug 1 and wiper, where the pitch eye would go
LDR_V1 / LDR_P2	The vactrol's photocell. LDR_V1 and LDR_P1 are one strip and LDR_V2 and LDR_P2 the other, so it sits in parallel with PITCH
LED_A / LED_K	The vactrol's LED, sealed to that photocell
SPK_A / SPK_B	The line out: tip to SPK_A, sleeve to SPK_B
VR2_1 / VR2_3	The blend pot, lug 1 and lug 3. Its wiper goes to the common of the on-off-on toggle
P5_1 / P5_2	The wobble. One throw of the toggle goes to lug 1 of the dual pot's first gang, whose wiper lands on P5_1, IC1's pin 5. The other throw goes to the second gang, whose wiper lands on P5_2, IC2's pin 5. Center is off
CV	The CV in jack's tip. R10, 47K, is on the board
VR1_3 / VR1_W	The rate pot, lug 3 and wiper
LED2_A / LED2_K / RATE_LED	Nothing in this box. They are the Opto Duet's indicator and the LFO's rate LED, left on the board for anyone who wants them back

Built, and heard

Built on two boards - my Opto Duet v2 and my Dual-Wave LFO - wired the way this page describes, and it sounds great. The dual pot has nothing in series with it on purpose. At the bottom of the knob the LFO drives pin 5 directly and it gets noisy, and I like it noisy, so it stays that way.

The Opto Wobble opened up and held in one hand over a workbench: a glittery pink 125B enclosure lying on its back with two pieces of stripboard mounted inside, one at the left carrying a row of small resistors and a white wire link, one in the middle crowded with parts, and bundles of orange, black, yellow, blue and green wires running from them to the round metal backs of the pots and to the jacks at the far end. Pliers, a glue gun, a spare jack and a pot lie on the bench around it. — Mine, open: the Opto Duet v2 and the Dual-Wave LFO on their own two boards in a pink 125B, which is the build this page is drawn from.

Hear it: the box standing up with the lid on, turned by hand. 8 seconds, sound on.

How it works, in one breath

A 555 decides when its timing cap is full by comparing it against a reference, and pin 5 is that reference. It normally sits at two thirds of the supply on an internal divider, with a 10n cap to hold it steady. Push pin 5 up and the cap has further to charge, so the chip slows down; pull it down and it speeds up. So the LFO on pin 5 of the engine wobbles the tempo of the flashes, and on pin 5 of the voice it wobbles the pitch. The dual pot is how hard it pushes: turned up it is a gentle sway, and at the bottom there is nothing between the LFO and pin 5, so it overpowers the reference and the chip starts to chatter. That is the noise.

The CV input is the same idea from outside the box. R10, 47K, keeps whatever you plug in from overpowering pin 5, so a CV bends the engine's tempo rather than grabbing it. The LFO itself is the Dual-Wave LFO exactly as its own page describes it, running from the Duet's protected rail.

Things to try

None of these have been tried. They are the obvious knobs.

A floor under the dual pot. 10K to 22K in series with each gang keeps the wobble clean all the way down, if you want a sway and never the grit.
The eyes back. Photocells on the LDR_T and LDR_P pads instead of the TEMPO and PITCH pots, the Opto Duet's way, and the room light plays it again.
CV into the voice. A second 47K from a second jack onto P5_2 does for the pitch what R10 does for the tempo.
Clock it from the Spider Sequencer into the CV input, and each step moves the engine.

Two of my own layouts on one board: the Opto Duet, whose engine-and-voice arrangement is mine, and the Dual-Wave LFO, whose triangle-and-square pair came from the Experimentalists Anonymous archive. The wobble wiring, the layout and the words are Onion Madder's, drawn in Copper Bottom.