Build the Arduino Pocket Piano

Ever wondered how the Arduino would fair as a keyboard synthesizer? Wonder no more – the Pocket Piano kit from Critter and Guitari proves Arduino can sine and saw quite well. Features include –

• 25 keys and multiplexer circuitry
• 4 potentiometers, 1 controls output level
• Microchip MCP4921 12 bit SPI DAC
• Passive low pass output filter

The kit comes with all the support hardware needed to turn the versatile micro into a sweet digital sound synth ready for experimentation. Sporting 2 octaves worth of key/switches and 4 full-size pots, it’s a relatively long board (over 3 Diecimilas long) – but the assembly is still quite simple.

Read on for construction pictorial and info.

Parts list

• A – PCB
• B – Male header pins, strip of 28
• C – Resistors
  10KΩ x6 (brown, black, orange)
  220Ω x1 (red, red, brown)
  4.7KΩ x1 (yellow, violet, red)

• D – Capacitors
  1µF (105) x1 (“105”)
  .1µF (104) x4 (“104”)
  .01µF (103) x1 (“103”)

• E – Potentiometers
  10KΩ x4

• F – RCA jack
• G – LED 5mm red
• H – ICs
  74HC4051 multiplexer x3
  MCP4921 12-bit DAC x1

• I – -Tactile switches x26

1 – Snap in the switches

We’ll start with the tactile switches because their satisfyingly fun to pop into place.
Turn the board over with the small numbered labels facing down. While supporting the pcb from below snap each of the 26 tactile switches in place – insert one side’s legs, then firmly press in the other side.


Flip the board over and solder the legs of each switch. 26 switches x 4 legs a piece = this will take a little while.

2 – Resistors

The resistors will be mounted standing vertically, we need to pre-bend them in the above manner so they’ll slip into pcb nicely.

Place each resistor into it’s appropriate location – standing on the silkscreened side of the board. You’ll notice one pad is labeled “330”, this is a misprint – so use the 220Ω there instead.

• 10KΩ x6 (brown, black, orange)
• 220Ω x1 (red, red, brown)
• 4.7KΩ x1 (yellow, violet, red)

Bend each resistor’s lead flat to the board to keep them upright and then solder each to its respective pad.

Once they’re securely soldered clip each excess lead with a pair of nippy clippers or similar tool.

3 – Capacitors

Place each capacitor in its appropriate spot on the board. Be sure to read their labels carefully as they’re quite small and easily confused

• 1µF (105) x1 (“105”)
• .1µF (104) x4 (“104”)
• .01µF (103) x1 (“103”)

Bend the leads, solder, and clip – just as with the resistors.

4 – IC chips

The IC’s need a little preparation before settling into their new homes. You’ll notice each chip’s pins splay out a bit – carefully press each side against a flat object until they stand perpendicular to the IC’s body, pretty much any sturdy plastic surface will work.

Orient the chips on the board so that their notches match the silkscreened labels, and settle them into the solder padded holes.

It’s helpful to bend some of the protruding leads, in order to secure the chips while soldering.

Solder the IC’s into place, while taking care not to overheat the chip’s body while soldering.

5 – Pin headers

Now we need to divide up that 28-pin header into 4 pieces – 2 8-pin strips, and 2 6-pin. Count the necessary sections and separate them with your clippers – keep each side somewhat secured by hand – they tend to fly off during clipping.

Set each row of pins in place on the labelled side of the board, with the longer ends facing upward. While keeping them perpendicular to the board, use a piece of tape to temporarily secure each strip in place.

Turn the board over and solder each pin cleanly to its pad, ensuring none of the solder bridges between the contacts.

6 – LED

the LED needs to sit lens-up on the labelled board side. Add the LED to it’s spot in middle of the wider end of the pcb paying close attention to its orientation. The longer should be closer to the corner of the pcb with 3 large mounting holes (that’s where the RCA jack will go)
Bend the leads, solder, and clip.

7 – RCA jack

snap the RCA jack into place on the labelled side of the board. Solder somewhat liberally to provide a durable audio connection

8 – Potentiometers

Now we get to the big parts – the potentiometers go into shaft facing up on the along the edge of the non-labelled side of the board. Use plenty of solder to keep their relatively large weight secure during use. Once soldered, clip each lead carefully to avoid airborne clippings!

And then – oh wait, that’s all for soldering. Time to introduce Pocket Piano to its Arduino core –

9 – Connect Arduino, upload software

Line up the appropriate length pin strips to the Arduino’s female headers. The boards should only properly fit together one way – the right way, with Arduino’s USB and DC jack jutting out from below the Piano board’s wider end. Slowly and firmly press the two board’s together till they fit flush with one another.

Now plug the Arduino into your computer’s USB port and get to the uploading! Pocket Piano sketches are available for download from Critter and Guitari’s site.

Once you’ve loaded up one of the programs, and connected the RCA jack to a stereo/amplifier – MAKE SOME MUSIC!