Check all the connections on the
breadboard carefully. When you’re satisfied
they’re okay, you can attach the Arduino.
For convenience, I first attached the Uno
and breadboard to a small Perspex carrier plate.
You can see this in Figure 4. You can often buy
an Uno, half size breadboard, and plate as a kit.
Connect the Uno 5V pin to the 5V rail of
the breadboard, and the Uno GND pin to the
GND rail. Connect Uno pin 1 (TX0) to the
220R resistor that goes to pin 5 of the MIDI
socket. This is the serial transmit output from
the Uno, and it’s where we will output our
Note On events.
I used Dupont male-to-male 10 cm jumper
cables to connect the Uno to the breadboard.
Now, connect up the MPR121. This communicates
with the Uno using the I2C serial protocol, so you only
need two wires. Connect Uno pin A4 to SDA (the data
line) and Uno pin 5 to SCL (the clock).
That’s all the connections needed, and the electronics
are now complete. Now would be a good time to check
all the connections again!
The MIDI lyre has 12 strings made of 2 mm carbon
fiber rod. To make the strings, buy four pieces of 1 m
long/2 mm diameter extruded carbon fiber rod. This is
readily available for a few dollars in hobby shops or online
because it’s often used in RC planes, cars, and drones.
Cut each rod into three equal 333 mm lengths using a
hacksaw or (if you have one) a bandsaw. I find it useful to
tape all the rods together using masking tape and then
mark and cut them all at once. The rod is surprisingly easy
to cut even by hand.
The length of the strings is not critical, so if you want
to make them a bit shorter or longer, it should be no
problem. In fact, 25 mm is also
a good length because you
can get four strings from a 1 m
In an acoustic lyre, the
strings are stretched over a
bridge to a neck where they
are tensioned by some sort of
tuning machines that are
usually simple pegs. To create
the bridge and the neck of the
lyre, use two 12-way terminal
barrier block strips with a 12
mm spacing between terminals
(this is usually the 15A rated
Make sure you get the
simple kind of strip that has brass tubes in which the wires
are secured with small bolts. Other fastenings are
available, but they may not accept the 2 mm carbon fiber
String spacing is not critical. It’s largely a matter of
personal preference and what terminal block spacings are
readily available. If the strings are too close together, it’s
hard to play individual notes. If the strings are too far
apart, it’s hard to strum the instrument.
I find that 12 mm is a decent compromise that allows
me to use off-the-shelf terminal blocks. Of course, if you
break the terminal block up into individual terminals, you
can have whatever string spacing you want! In fact, you
can arrange the strings however you want, and make a
whole range of other instruments! For the MIDI lyre, it’s
convenient to keep the blocks in one piece.
Stringing the MIDI lyre involves fixing each carbon
fiber string between the bridge and neck terminal blocks.
There is an easy way to do this and a hard way.
The hard way is (sadly) the more obvious way, so we
need to discuss it so you don’t waste your time on it. This
is to fix each string in the bridge terminal block and then
July/August 2018 29
■ FIGURE 5. Photo of a female five-pin DIN MIDI socket suitable
for mounting on a breadboard.
■ FIGURE 6. Diagram to show correct wiring of a MIDI out socket. Note that the
socket is viewed from the back so you can see exactly what pins to connect to.