Switch Holes

The bottom of the medium sized drawer will become the front panel of the Ambient Sound Machine.

Use the drilling template linked below to print out a guide for drilling the switches. Then, use a center punch and a 6mm drill bit (15/64" if using Imperial) to create all 20 holes for the toggle switches.

If you have access to a laser cutter this can be a very quick way to create the holes, as shown here.

Switch Ground

You can use the medium box as a jig for the switches while soldering the center position tabs to a common ground line.

Just put the switches into the panel backwards (from the outside-in), then use short lengths of black wire to solder the center lugs.

You can do a couple of rows at a time, then flip them and screw them in from the inside. This keeps things a bit more manageable than trying to do all 20 at once.

Switch Pins

You'll use the arcade quick connect cables to connect the GPIO expanders to the switches. 

Clip the JST connector off and then strip and solder the wires as shown.

Then, plug the spade connector of each wire into its associated switch lower lug as shown.

Then, add the second two sets of switches with their common grounds soldered.

Do this for the first ten switches using the first expander board.

Second Set

In order to use both expander boards on the I2C bus, you'll give the second one a unique address. Heat a blob of solder across the pads for the Addr +1 jumper as shown.

Then, solder the wires and connect the lower lugs as before.

Grid Layout

Use M2.5 nylon screws and standoffs to fasten the boards to the mounting grid.

This is a suggested layout you can use, as well as a photo with the wiring connected as per the circuit diagram.

You can use zip ties to neaten the wiring before assembling into the case.

Speaker Enclosure

Drill or laser cut holes into the back of the small MOPPE drawer to act as a speaker grill and mounting surface for the speaker. You can use the .svg file provided below to get the hole spacing correct for the speaker's four mounting points.

You'll also use a Forstner bit or hole saw to make a hole for the panel-mount USB-C connector.

Push the USB-C panel connector into the hole from the outside and screw the retaining nut in from the inside.

Optional Switch Locks

Rather than drill/cut 20 tiny holes to register the anti-twist tab of the switches, I decided to cut small plywood switch body locks, as shown here. They are glued in place to the inside of the front panel.

Feet

Cut four feet from 1/2" x 1-1/2" poplar or similar hardwood.

Glue and clamp them to the larger MOPPE drawer/front enclosure as shown.

USB Cable

Assemble the DIY USB-C cable for the inside of the box by pulling the gray retention clip out a tiny amount, then inserting the ribbon cable end with the metal conductors visible from the top side of the board as shown. When fully inserted, press the retaining clip back in to secure the cable.

Repeat for both ends.

Close it Up

Place the grid/circuit into the enclosure as shown. The back enclosure will hold it in place.

Plug in the USB cable to connect the Metro M7 to the USB panel mount.

Then, place the back on. It will fit snugly over the switch lockers.

Fill the gaps above and below the small drawer with additional strips of hardwood.