Pico 2 Piano W/ CircuitPython

This instructable will describe how to assemble an electronic piano with one scale based off of a Pico 2, a speaker, and an amplifier. This project has a nice balance of coding, assembly, laser cutting, soldering, and breadboarding, making it a perfect intro for hobbyists looking to expand their skills and use a wide range of tools.

The above picture shows all the resources that this project needs. Namely,

1. Pico 2
2. Amplifier--I used the pam8302a from adafruit, which went nicely with
3. Speaker! I used a 4 Ohm 3 Watt speaker, but depending on how much sound you want, you might need a different speaker and amplifier
4. Misc items
5. Breadboarding wires (a lot, if you want any sort of organization. Many nice kits online)
6. Breadboards--I used four, but with some soldering and longer wires, you could pretty easily get away with just one. The more breadboards you have, the easier it is to modify.
7. Buttons! 12, to be precise. They will go under the piano keys. But get some extra, in case you mess up the soldering.
8. A resistor and a capacitor. We are going to be making a low-pass filter which this requires. I used a 110 pF capacitor and a 1K ohm resistor, but your mileage may vary.

The basic board set up is fairly simple. Put your pico 2 and the amplifier on the same board. Connect the Pico 5V to the positive channel and its ground to the ground. The low pass filter is made by putting a resistor in between the audio out pin (I used GP15) and the A+ on the amplifier. Then, connect the capacitor from the A+ pin to ground. This will cut out frequencies from the noisy PWM that we don't want (see https://www.electronics-tutorials.ws/filter/filter_2.html). The rest of the pinouts for the amplifier are as follows:

1. Vin to 5V
2. Ground to ground
3. SD wired high
4. A- tied to ground

And boom! If you connect your speaker and play audio out of the pin the filter and A+ pin are connected to, you should hear some sweet tunes.

Soldering the buttons is pretty easy. I flattened the connectors and snipping all but two on one side off, so that fitting them in is easier. Then, simply solder two wires onto the ends of the buttons. Make sure the wires are long enough that they can make it out from under the keys of the piano.

I CAD'd up the design of the piano which is attached below. The keys need to be printed 12 times, and the pin should be printed twice and glued together. The piano is split into two parts so that it can be printed individually on a Bambu X1, but if you have a large enough printer to print it in one shot, go for it.

Next, put it all together by sliding the keys on the pins, and putting it in the piano chassis. Make sure all the keys line up in their respective slots. Then, hot glue the buttons into the chassis. I put my buttons about 3/4s of the way towards the front, but depending on where you put them the travel of the keys will feel a little bit different.

How you decide to wire the piano depends on a lot on the length of wire you used and how comfortable you are with ugly breadboarding. For my part, I decided to pre-wire four connections from the pico 2 to the edge of three breadboards. Then, I plugged in the buttons wherever they would reach, and then connected the positive sides of the buttons to the edges of their respective breadboards. This has the benefit of making the wiring a little easier to look at and means a lot of the wiring can happen before assembling the whole thing.

Box assembly! This box will have our electronics and be our mounting point for the speaker. I used MakerCase to make a box, 14.2"x4"x4". I also cut a square hole on one of the sides to mount the speaker. One long side of the box is cut in half to make space for the wires. Then, stuff the breadboards in in whatever way will fit, mount the speaker in whatever way you'd like, and boom. I have the piano chassis and the box placed on a large wood cutout to support them while transporting the piano.

You should have a fully assembled piano. If you don't want to do the coding yourself, I've attached my circuitpython file below. But if you want to do it yourself, the basics are this: I have 12 note files that get played whenever you press a button. Because they are wav files, they cannot combine, so only one plays at a time. We use an audiomixer to make things a little bit easier when iterating by index.

Get the notes zip file at this link: https://drive.google.com/file/d/1uxE-Jy5FegDZgQa-IatRRXN9iwywkAlL/view?usp=sharing

Here are some ideas to extend the implementation of your project:

You can add a potentiometer to one of the ADC pins on the Pico 2 to control the volume. That allows the user to control the volume to their liking.

Adding colored strips or printing some of the keys in another color can make your keyboard more resemble an actual piano. Place the different colors on the flats and the sharps.

Adding bigger speakers! This might require a new case that can fit the speaker and possible a larger amplifier. However, with your new volume control, you should be able to get full usage out of whatever speaker you choose.

Lights--adding lights or LEDs that are activated when a button is pressed is a very simple addition to the wiring--just put the lights in series with the button, and boom--light reactivity!