The Hardware
The key idea behind the design is using copper (or aluminium) tape
around the base and each key and connecting each key's tape to a
GPIO output on the Raspbrry Pi to determine whether or not a key is
pressed by checking whether or not the circuit was closed. This
design results in keys which feel unchanged from those the original
set, and hardware that can be built without needing to get a bunch
of switches or printing a circuit board. In these pictures, I used a
mix of aluminium and copper tape, but practically, it doesn't
matter. If your tape is thin, it might tear easily - an easy fix for
this is just to double up.
We start by building just the keyboard portion of the Lego set (this
starts at bag 11 of the instructions) - we'll revisit the rest of
the set once this is working reliably. If your piano is already
built, take it apart and lift out the keyboard and power functions
assemblies so that you can work on the areas in the following
pictures - it's annoying, but not as tricky as it looks, based on my
experience. Once that's done, we'll wrap the entire base underneath
the keys in tape (or the individual plates which are then linked) -
this will be our ground once we connect it to the Raspberry Pi's
ground. To do this, connect it using the tape across the bottom of
the base so you can connect to the Raspberry Pi ground wire on the
other side (remove the Dupont connector using the tweezers, and wrap
the tape around the end of the wire). We also add a wire on 25
separate GPIO pins starting from 2, and an additional wire for
ground (consult a pin map of your model for this step). We haven't
yet built the switches, but this is a good time to test out the
software by manually closing the circuits and making sure the keys
on the UI light up/produce sound.
Take apart the bottom of a key (the three pieces under the long
brick)
Slightly pry open a paperclip, so that it can lay within the 3x1
brick. Seal it in with the 3x1 plate between the sides of the
paperclip
Cut long strips of tape that are just a little less than the width
of the thin part of each key. Lay them along the length of each key
so that they lay over and secure the exposed part of the paperclip
(eyeballing the length usually works, and you can fix this with more
tape anyway).
Use the cone that the key rests on to poke a hole in the tape where
it would normally go. Cut a thinner strip of tape along the side to
reseal this, and check that the connection still works.
For the black keys, the tape should go over the edge slightly, but
it can stop a bit before the edge for the white keys. The only
important thing is that they connect to the base when pressed down,
so check the connections.
Remove the Dupont connectors from the ends of the wires using
tweezers, and bend them around the ends of each paperclip (be
careful - use the tweezers for this). Secure the connection with the
tape. Repeat the process with each key in order. Try not to mess up
the key order, but if you do, the software can allow you to remap
the keys (as long as you have connected the wires to GPIO).
Don't forget to connect the ground wire to the base
Once again, it's a good idea to check the connections before
proceeding.
Now we get back to building the piano. Ignore the transparent tape
on top of the keys in these pictures - these pictures were from the
old switch design, but the steps from this point on are the same.
We're going to build the rest of the Piano around the keys. Starting
from the beginning, we omit the portion where we add the bracket for
holding the power functions battery box included with the set (since
we don't need it), but otherwise proceed as usual until step 76.
The next pictures show the differences in the next few steps. We use
the parts from these sets to seal in the wires between the keys and
the Raspberry Pi, and try to orient it so that the ports are easily
accessible from the right side panel, (and/or add a battery bank
here if we want it to be entirely wireless).
Make sure everything works before you seal it in. We then build the
rest of the piano as usual. The only other tricky part is step 288,
but isn't too bad if the keys are handled a little carefully.
Once we're done, the Raspberry Pi should be accessible from the side
panel, so we can plug it in, add a power bank, etc.
