Nuts and Volts - July/August 2018

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 consecutive!

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 octave.