picoslidertoy

Table of contents

• What is it?
• Variants
• Parts needed
• Soldering components
• Firmware installation / Installing apps
• Why?

What is it?

picoslidertoy is a touch-sensitive control surface that uses 24 GPIO pins of the Raspberry Pi Pico to provide:

• three linear sliders
• two rotary sliders
• nine buttons
• all capacitive touch

It also includes a cutout for a reverse-mounted SSD1306 I2C OLED display. The Raspberry Pi Pico SMD mounts to the back of the board to provide a clean look for the touch surface. The entire PCB is 165 mm x 76 mm (6.5" x 3.0").

The picoslidertoy can be a USB MIDI control surface, a USB Macropad keyboard with "analog" controls, or even a USB gamepad. It can be programmed in CircuitPython and touchio or Arduino with my TouchyTouch library. Several example firmware apps are provided.

Variants

There are two versions of the picoslidertoy available:

• black PCB -- production version with proper alignment of the cutout for standard 0.96" I2C OLED, comes with all SMD resistors soldered down Note: the silkscreen on the back has a typo, saying 0.91" I2C OLED.

• green PCB -- prototype version with no components soldered down and where the I2C OLED display cutout is a little off. Still usable, or mount the display on the face.

There is also a nice minimal 3d-printable enclosure available in the github repo (and visible in the photos above). You really want a case for capacitive touch projects like this to reduce spurious readings.

Parts needed

In addition to the picoslidertoy PCB, you will need:

• Raspberry Pi Pico

  • Must be w/ castellated pads & w/o headers, (like this)
  • For USB-C, consider this USB-C 16 MB Pico clone
  • (NOTE: NOT the Pico2, since its RP2350 chip has a hardware error)

• I2C OLED display SSD1306

  • 0.96" 128 x 64 pixels, in white
  • Pins must be in GND,VCC,SCL,SDA order
  • Prefer the 27.5 mm wide displays over the 25 mm wide ones (one example)

• (If you have a green proto one, you will also need 24 x 1M 0603 resistors and 2 x 10k 0603 resistors)

• 3d printed case or M2.5 standoffs/screws or some other feet

Soldering components

• Pico -- the Pico is soldered down surface-mount style, using its castellated pads. This video soldering a Pico on picotouch is how I do it for this board too. It's technically surface-mount soldering, but the pads are bigger than most through-hole pads and easy to solder to. Note that Pico clones that don't have castellated pads like the real Pico will not work. (Youtube video with Pico SMD soldering tips)

• OLED Display -- the display can either be mounted on the front (especially easy if your display's pins come pre-soldered) or from the back (my preference). If mounting from the back, you first need to desolder the 4-pin header on the display and mount a new 4-pin header "reverse" so that pins stick up from the front of the display. The main header body is still on the back of the display. (The video below hopefully makes this clearer). When soldering, do one pin first and check alignment, then solder the rest of the pins. Finish up by trimming the excess header pins. (Youtube video with picoslidertoy soldering tips)

Firmware installation / Installing apps

CircuitPython apps

These are the apps currently available

• hwtest -- a simple on/off test of the touch sensors, no display needed. Use serial REPL to see results

• hwtest display -- like hwtest but also outputs simple feedback via the display

• midi_sliders -- MIDI controller where the sliders emit CCs and the buttons send NoteOn/NoteOffs

If you've never used a Pico or CircuitPython, there are several ways to put code on it. The two main ways I'll present here are:

• Ready-to-go UF2 file in "Releases"
• Installing by hand: CircuitPython, code.py, libraries

Ready-to-go UF2 file

Steps to install a UF2 file:

• Download a ready-to-go UF2 file from the Releases section section
• Hold the BOOTSEL button on the picoslidertoy's Pico while plugging it into your computer
• Copy the UF2 file to the "RPI-RP2" Pico bootloader drive
• Wait for a bit, then app is running!

In general, I'll try to make UF2 files available in the Releases section for the different apps.

Installing by hand

Steps to install by hand:

• Download this repo, either with a git clone or clicking on "Code / Download ZIP"

• Download the latest CircuitPython UF2 for Pico at https://circuitpython.org/board/raspberry_pi_pico/

• Install the CircuitPython UF2 (like in the above UF2 steps)

• Wait for CircuitPython to come up and present a CIRCUITPY drive

• Copy the files of the picoslidertoy app in question to CIRCUITPY:

  e.g. for midi_sliders, copy code.py, slider_display.py, touchslider.py to CIRCUITPY

  cp circuitpython/midi_sliders/* /Volumes/CIRCUITPY  # (if macos)
  

• Install CircuitPython libraries onto Pico

  If you have Python on your computer you can do:

  pip3 install circup
  circup install adafruit_midi adafruit_displayio_ssd1306
  

  Otherwise, download the CircuitPython Libraries Bundle and copy over the adafruit_midi and adafruit_displayio_ssd1306 libraries to the CIRCUITPY/lib folder on the Pico.

Why?

I wanted a way to experiment with linear and rotary touch sliders. I made some touchwheels to give away for Hackaday Supercon 2023 and they were popular. I wanted a larger playground for experimenting with these controls.

What makes it special?

The 24 capacitive touch sensors are read directly by the Pico, either via CircuitPython's touchio library or the TouchyTouch Arduino library. No external touch chip needed. I think that's really cool! Getting an "analog" value out of the three touch sensors that make up a linear or rotary touch slider is fairly simple but there are some tricks I'm developing to make the values stable.

picoslidertoy is also completely open source with schematic files in KiCad and software in CircuitPython and Arduino.

Press links

• Adafruit Show-N-Tell Live show 10 Apr 2024
• Hackster.io 11 Apr 2024 article