The electronics cavity is made on the side of the plank, as shown
in the drawing above.
Pre-drill a 30mm-deep and 60mm-long cavity with a 1" (25mm)
Forstner drill bit and finish with a 1"(24mm)-wide chisel.
Finally, use a 1/4" (6mm) bit to drill a channel to connect
the pickup cavity with the electronics cavity.