4-axis robot controller

# KB2040 4-Axis Robot Arm Controller

USB controller for a 4-axis robot arm using an Adafruit KB2040 (RP2040). Four potentiometers for axis control plus a button for gripper/trigger — all read over a simple serial protocol.

## BOM

| Part | Qty |
|---|---|
| Adafruit KB2040 | 1 |
| 10kΩ linear potentiometer | 4 | WWZMDiB
| Tactile push button (momentary) | 1 | US-SKU E429
| 3D-printed enclosure | 1 |
| USB-C cable | 1 |

## Wiring

| KB2040 | Connected to |
|---|---|
| A0 (GP26) | Pot 1 wiper |
| A1 (GP27) | Pot 2 wiper |
| A2 (GP28) | Pot 3 wiper |
| A3 (GP29) | Pot 4 wiper |
| Pin 9 (GP9) | Button (other leg → 3.3V) |
| 3.3V | Pot 1–4 left leg |
| GND | Pot 1–4 right leg, button pull-down |

Potentiometer legs: left → 3.3V, right → GND, wiper (center) → analog pin.

Button is active-high (press sends 3.3V to GP9). The firmware uses the RP2040's internal pulldown so no external resistor is needed.

## Firmware

Uses the [Earle Philhower RP2040 core](https://github.com/earlephilhower