Keypads
Sixteen keys can consume eight GPIO pins, one ADC input, or two I2C lines — depending on whether the pad is matrix-scanned, a resistor ladder, or handled by a controller chip.
Matrix keypads, analog ADKey boards, I2C keypad controllers, joysticks, and finished USB-HID keyboards are all here. Pin budget and simultaneous-press requirements are the splits that matter.
- A bare 4×4 matrix keypad uses 8 GPIO for row/column scanning; the TCA8418 breakout and Adafruit Trellis/NeoTrellis PCBs offload scanning and LED driving to a dedicated chip over I2C.
- Resistor-ladder pads — Fermion ADKey 10-key, Gravity Analog ADKeyboard V2 — return a single voltage on one ADC pin, which costs almost no pins but rules out simultaneous keypresses.
- Joysticks span three tiers: the bare PSP 2-Axis Analog Thumb Joystick (two ADC channels), M5Stack I2C Joystick 2 Unit (STM32G030 onboard), and the USB-HID Thumbstick Trinkey.
- Kailh MX/CHOC key switches, switch sockets and the Keybow/UNTZtrument kits are build-your-own territory; the CardKB2 (ESP32-C61, I2C/UART/BLE HID) and MaKey MaKey are finished input devices.
