The Machine · Control
Design stage
Updated 2026-10-19
Patch cords between elements and loops, like an old telephone exchange, for an installation that visitors play.
Loading the model
Drag to turn · scroll to zoom
Printed
| Kind | Part | Qty | Each | File |
|---|---|---|---|---|
| Printed | Panel tile, lower leftYour choice: see The panel | 1 | · | STL |
| Printed | Panel tile, lower rightYour choice: see The panel | 1 | · | STL |
| Printed | Panel tile, upper leftYour choice: see The panel | 1 | · | STL |
| Printed | Panel tile, upper rightYour choice: see The panel | 1 | · | STL |
| Fabricated | The Bridge, built in its boxIts own recipe. It sits on the right foot, behind the panel, where only whoever looks after the installation reaches its stop. | 1 | · | |
| Bought | 2020 V-slot extrusion, 280 mmThe feet, front to back. | 2 | $3.00 | |
| Bought | 2020 V-slot extrusion, 400 mmThe side uprights. | 2 | $4.00 | |
| Bought | 2020 V-slot extrusion, 360 mmThe top and bottom bars, and the middle upright the tiles meet on. | 3 | $3.50 | |
| Bought | Corner brackets for 20 mm extrusion | 10 | $0.50 | |
| Bought | M5 x 10 screws and T-nutsFor the brackets, the tiles and the bridge box. | 34 | $0.30 | |
| Bought | 1/4 inch mono panel socketsYour choice: see The sockets and cordsSixty-four for the loops, eight for the elements. | 72 | $0.80 | |
| Bought | 1/4 inch patch cords, about 1 mYour choice: see The sockets and cordsGuitar patch cables. One for each element. | 8 | $3.00 | |
| Bought | MCP23017 I/O expander boardGoes inside the bridge box, beside the board. | 1 | $3.00 | |
| Bought | Ribbon or multi-core cable, 17 cores, about 1 mFrom the sockets to the bridge box, in through its cable slot. | 1 | $4.00 | |
| Bought | Bare tinned wireDown each column, joining its eight sockets' tips. | 1 | $3.00 | |
| Total | $131.30 | |||
Decisions that are yours to make. Where we started is the version in the 3D model and the ingredients: a starting point, not the right answer.
What do visitors plug in?
Big, solid plugs that click home and stand a lot of handling. Cheap cords anyone can replace.
Smaller and cheaper, and the board can be half the size. Fiddly for big hands, and the plugs wear sooner.
Coloured, springy plugs like an old laboratory, one wire each. A different colour for each element reads at a glance.
What is the face made of?
In the same orange as every printed part, and any change to the layout is a new print. About 45 hours of printing.
A single 6 mm sheet, drilled. Warm, like a wooden exchange cabinet, no seams, and no printing.
2 mm, drilled and labelled with engraving or stamps. The most like the real thing, and the heaviest.
Behind the board, or with the attendant?
One thing to set up, and the stop is a step behind the board, out of visitors' reach.
The bridge box on a desk a few meters off, joined by a longer cable, so whoever looks after the room has the stop at hand all day.
Each tile is 200 x 210 mm and prints flat. The socket holes are 9.6 mm, for the 3/8 inch thread of a standard 1/4 inch panel socket; check yours before printing.
Panel tile, lower left
Panel tile, lower right
Panel tile, upper left
Panel tile, upper right
Build the frame. Stand the two side uprights on the feet, then fit the bottom bar, the top bar and the middle upright between them, all with corner brackets.
CheckThe frame stands square and doesn't rock, and the middle upright is centred.
Push the 72 sockets through the four tiles, eight to a column and eight along the bottom row, and tighten their nuts on the face.
TrickyTurn every socket the same way, tip lug up. The column wiring runs straight down the lugs, and a socket turned sideways leaves its lug out of line.
Run one bare wire down each column, soldered to each of its eight sockets' tip lugs.
CheckWith a multimeter, every tip in a column connects to every other, and to nothing in the next column.
Screw the four tiles to the frame with M5 screws into T-nuts in the uprights and bars.
Screw the bridge box to the top of the right foot, behind the panel, with two M5 screws into T-nuts.
Wire the expander inside the bridge box, and run the ribbon cable from it to the sockets as in the Wiring tab.
TrickyLabel both ends of every core as you go. Seventeen cores look alike once they're in the box.
Plug one end of each patch cord into its element's socket along the bottom row, and hang the free ends below.
CheckWith a multimeter, each element's tip at the expander end connects to the column its cord is plugged into, and to no other.
The bridge is wired as on its own recipe. Here is the Switchboard's own part: the expander, inside the bridge box, sends a signal down each element's cord in turn and listens on the eight loop columns. A cord from element 3 in column 5 means element 3 plays loop 5. The sockets' sleeves connect to nothing.
ESP32-S3 board, in the bridge box, 3V3
MCP23017 expander, in the bridge box, VCC
PowerAny hookup wire
ESP32-S3 board, in the bridge box, 3V3
MCP23017 expander, in the bridge box, RESET
PowerAny hookup wire
Held high, or the expander keeps resetting.
ESP32-S3 board, in the bridge box, GND
MCP23017 expander, in the bridge box, GND
GroundAny hookup wire
ESP32-S3 board, in the bridge box, GND
MCP23017 expander, in the bridge box, A0
GroundAny hookup wire
A0, A1 and A2 all to ground, for the expander's first address.
ESP32-S3 board, in the bridge box, GND
MCP23017 expander, in the bridge box, A1
GroundAny hookup wire
ESP32-S3 board, in the bridge box, GND
MCP23017 expander, in the bridge box, A2
GroundAny hookup wire
ESP32-S3 board, in the bridge box, GPIO 8
MCP23017 expander, in the bridge box, SDA
SignalAny hookup wire
ESP32-S3 board, in the bridge box, GPIO 9
MCP23017 expander, in the bridge box, SCL
SignalAny hookup wire
MCP23017 expander, in the bridge box, GPA0
Element sockets, along the bottom, Tip 1
SignalOne core of the ribbon
GPA1 to GPA7 go to elements 2 to 8 the same way. The expander pulls one element low at a time.
MCP23017 expander, in the bridge box, GPA1
Element sockets, along the bottom, Tip 2
Signal
MCP23017 expander, in the bridge box, GPA2
Element sockets, along the bottom, Tip 3
Signal
MCP23017 expander, in the bridge box, GPA3
Element sockets, along the bottom, Tip 4
Signal
MCP23017 expander, in the bridge box, GPA4
Element sockets, along the bottom, Tip 5
Signal
MCP23017 expander, in the bridge box, GPA5
Element sockets, along the bottom, Tip 6
Signal
MCP23017 expander, in the bridge box, GPA6
Element sockets, along the bottom, Tip 7
Signal
MCP23017 expander, in the bridge box, GPA7
Element sockets, along the bottom, Tip 8
Signal
MCP23017 expander, in the bridge box, GPB0
Loop columns, eight sockets joined in each, Column 1
SignalOne core of the ribbon, to the column's bare wire
GPB1 to GPB7 go to columns 2 to 8 the same way. Each column is held high, and reads low when the element being pulled low is plugged into it.
MCP23017 expander, in the bridge box, GPB1
Loop columns, eight sockets joined in each, Column 2
Signal
MCP23017 expander, in the bridge box, GPB2
Loop columns, eight sockets joined in each, Column 3
Signal
MCP23017 expander, in the bridge box, GPB3
Loop columns, eight sockets joined in each, Column 4
Signal
MCP23017 expander, in the bridge box, GPB4
Loop columns, eight sockets joined in each, Column 5
Signal
MCP23017 expander, in the bridge box, GPB5
Loop columns, eight sockets joined in each, Column 6
Signal
MCP23017 expander, in the bridge box, GPB6
Loop columns, eight sockets joined in each, Column 7
Signal
MCP23017 expander, in the bridge box, GPB7
Loop columns, eight sockets joined in each, Column 8
Signal
The Switchboard stands on the floor, its face to the room. Everything is 2020 extrusion joined with corner brackets, the tiles are screwed to its front, and the bridge box sits on the right foot behind it.
On its own feet, or against a wall?
Freestanding in the room, so visitors can walk round it and see the wiring behind.
Screwed to the wall through the uprights' back slots, with the feet left off. Steadier against a crowd, and the back stays out of sight.