hold them steady. Put the MPR121 board
down on top of them with its top surface
upwards so the pins go through the holes
in the board and solder the pins in place.
Make sure you have the board with its top
surface upwards, and you can’t go wrong.
Once the headers are soldered on,
insert the MPR121 into the half size
breadboard as shown back in Figure 2
and add the jumpers for VIN and GND.
The next step is to place the MIDI
socket on the breadboard. For
convenience, I used a PCB (printed circuit
board) compatible MIDI socket as shown
in Figure 5 that plugs directly into a
breadboard. However, you can also use a
socket with solder tags depending on how
you choose to construct your lyre.
The MIDI socket is a five-pin DIN
socket, but there are three different flavors
of five-pin DIN with different
arrangements of pins. Make sure you get
the MIDI version which is DIN 41524,
5/180°. This means there are five pins
with pins at 0°, 45°, 90°, 135°, and 180°.
Figure 6 shows a MIDI socket from the
back (the cable plugs into the other side),
so you can see exactly how to wire it up.
Notice that the pin numbering is not
Plug the socket into the breadboard,
then add the jumper between pin 2 and
GND; a 220R resistor between pin 4 and
+5V; and another 220R resistor on
pin 5 to a free row of contacts.
Next, you can add the octave up
and down pushbuttons. Any sort of
momentary action pushbutton will
do. I used tactile switches that are
compatible with the breadboard.
These are readily available from the
usual sources. One pole of each
switch goes to GND, and the other
will eventually go to a pin on the
Arduino. These pushbuttons are
optional; the lyre will work just fine
if you leave them out. However,
you will not be able to change the
28 July/August 2018
■ FIGURE 3.
of the MIDI
lyre on a
■ FIGURE 4. Photo of the
finished MIDI lyre electronics.
Note the two six-way ribbon
cables that go from the MPR121
to the strings.