PS4 Controller to Two LEGO Hubs — Johnny 5 Build

Date: 2026-09-23 Project: ps4-lego-bridge (also ps4-lego-onebrain) Status: ongoing Tags: esp32, bluepad32, legoino, nimble, btstack, lwp3, lego-powered-up, ps4, arduino

Context

Goal was to drive a Johnny 5 (Short Circuit) LEGO MOC — seven motors across two Technic (Control+) hubs — from a PS4 DualShock 4 via ESP32. The starting sketch combined Bluepad32 and Legoino on one ESP32 and failed to compile (Bluepad32.h: No such file or directory). The session went through a single-board attempt, then settled on two boards, then iterated the control scheme on a separate branch.

Key Decisions

Two ESP32 boards, not one. Bluepad32 uses BTstack (needed for BR/EDR — the DS4 is Bluetooth Classic); Legoino uses NimBLE. Two host stacks cannot share one radio/VHCI. Board A runs Bluepad32 only, board B runs Legoino only, linked by UART.
- Rejected: single-board via hand-rolled LWP3 GATT client on BTstack (ps4-lego-onebrain). It compiled and connected, but was far more code, an unresolved routing fault appeared, and the pivot made that moot. Kept as a separate repo, not maintained.
- Rejected: PS4-esp32 (Bluedroid) + BLE on one board — PS4-esp32 depends on internal Bluedroid symbols and is broken on modern cores.
ASCII UART protocol with XOR checksum over binary — debuggable with any USB-serial adapter. Receiver drops bad frames and stops all motors after 400ms of silence.
Tank drive, one input per motor. Arcade drive was tried first and rejected: mixing put one stick on both track motors.
Direction via DIR_* constants rather than editing signs inline — mirrored mountings are normal and flips should be one-line changes.
Board B pinned to arduino-esp32 core 2.0.17. Core 3.x breaks Legoino. Downgrading chosen over patching the library (patch is the first of several layers and gets reverted by Library Manager updates).
Arms moved to position control on the evolved branch: trigger position = arm angle, via setAbsoluteMotorPosition with BrakingStyle::HOLD. Rejected: power-based arm control with separate lower buttons — works, but the user wanted angle-proportional behaviour.
Arm encoders zeroed once per boot, not per reconnect. The hub retains its encoder preset; re-zeroing mid-session would redefine zero wherever the arms happened to be.
Separate branch johnny5-evolved for the new control scheme so main keeps the proven configuration.

Technical Details

Toolchain

Board	Package / library	Version
A	esp32_bluepad32	4.1.0
B	esp32 (Espressif)	2.0.17
B	NimBLE-Arduino	1.4.x
B	Legoino	latest

Bluepad32 board manager URL: https://raw.githubusercontent.com/ricardoquesada/esp32-arduino-lib-builder/master/bluepad32_files/package_esp32_bluepad32_index.json
Selecting the esp32_bluepad32 package starts BTstack before setup(). Any NimBLE sketch compiled under it aborts with ESP_ERR_INVALID_STATE at esp_bt_controller_init. Board B must use the plain esp32 package.
Core 3.x Legoino errors: 'string' in namespace 'std' does not name a type and no declaration matches ... ReadUInt32LE. Cause: ESP-IDF 5 made uint32_t unsigned long.

Wiring: A GPIO17 TX → B GPIO16 RX; A GPIO16 RX ← B GPIO17 TX; common GND (mandatory). Optional 5V→5V daisy-chain for single supply — never with both USB cables connected. LEDs on board B: GPIO25 and GPIO26, each via resistor to board B GND (not tapped off the UART ground wire).

Link frame: G,<lx>,<ly>,<rx>,<ry>,<buttons>,<dpad>,<l2>,<r2>*<XX>\n, 115200 8N1. Axes −512..511, triggers 0..1023, XX = XOR of payload.

Port map (verified on hardware)

hub0 90:84:2b:61:f2:d7 — A right track, B left track, C free, D body lift
hub1 90:84:2b:61:e6:8c — A left arm, B head tilt, C head turn, D right arm
Note: the two addresses were originally the wrong way round, and hub1 A/C and B/C were both mislabelled at points. All found by observation, not code.

Arm calibration: travel ≈ +280 (left) / −275 (right) motor degrees — under one revolution, so the single-turn absolute encoder is unambiguous. Spans set to ±250 to keep backlash clear of the end stop.

Rate limits: MOTOR_MIN_GAP_MS 100 (per port), HUB_MIN_GAP_MS 25 (per hub, ~40 cmd/s), ARM_MIN_GAP_MS 60. Hub1 carries four motors, hence the per-hub cap.

Arduino gotchas hit this session

The IDE injects generated prototypes before the first function definition. Types used in signatures (HubLink, PortState, ArmState, Frame) must be declared above it — broke the build twice.
Lpf2Hub::init() starts an asynchronous scan. Guarding it on !isConnected() && !isConnecting() re-enters NimBLEDevice::init() continuously and crashes. Use a one-shot initialised flag.
A scan that finds nothing ends silently; without a timeout the hub sits dead until power cycle. Fixed with scanExpiresAt / SCAN_TIMEOUT_MS (12s).
Bluepad32 keeps pairing keys in NVS; reflashing doesn't clear them. BP32.forgetBluetoothKeys() must be commented out after first pairing.

Startup order: wake both hubs (green button, blinking) → arms physically down → power board B. hub1 is only serviced after hub0 connects.

Code Changes

transmitter/transmitter.ino — frame extended with d-pad and analog triggers; DEBUG_FRAMES flag.
receiver/receiver.ino (main) — seven motors, tank drive, DIR_* constants, swapped hub addresses, right-arm button swap, types hoisted, core 2.0.17 noted in header.
receiver/receiver.ino (johnny5-evolved) — evolved scheme, position- controlled arms, GPIO LED toggles, head tilt/turn port swap, once-per-boot arm zeroing, scan timeout.
tools/arm_calibrate/arm_calibrate.ino — measures arm span in motor degrees (delivered as a file; Gitea push timed out — verify it's on the branch).
README.md (main) — build guide, toolchain table, power section, power-loss test, gotchas.

Evolved control scheme (johnny5-evolved)

Input	Action
Left / right stick Y	Left / right track
L2 / R2 analog	Left / right arm angle
L1 / R1	Head turn left / right
D-pad ↑/↓	Body lift
D-pad ←/→	Head tilt
Square	All stop (arms go limp)
Cross	Toggle 50/100% track speed
Circle / Triangle	Toggle LED pair 1 / 2

Open Questions / Next Steps

Head direction untested. DIR_HEAD_TURN and DIR_HEAD_TILT are +1 by default; flip if L1/R1 or d-pad ←/→ run backwards.
Scan timeout tuning. 12s is a guess; don't go below ~6s.
Power-loss test not yet run. The 400ms failsafe only fires if board B is alive. Cut board B's power with a track running and confirm whether the hub stops on BLE disconnect.
Heavy-load test. Both arms held mid-travel plus head swinging is the peak hub1 command load — check it doesn't drop.
Arm calibrate sketch — confirm it landed on johnny5-evolved.
Merge decision — johnny5-evolved into main once verified.
Boot track speed defaults to 50%; user may want 100%.

Artifacts

Repo: https://gitea.hideawaygaming.com.au/jessikitty/ps4-lego-bridge (branches main, johnny5-evolved)
Single-board attempt: https://gitea.hideawaygaming.com.au/jessikitty/ps4-lego-onebrain
Bluepad32 docs: https://bluepad32.readthedocs.io/
LEGO Wireless Protocol 3.0: https://lego.github.io/lego-ble-wireless-protocol-docs/
Device type IDs: https://github.com/pybricks/technical-info/blob/master/assigned-numbers.md
Legoino: https://github.com/corneliusmunz/legoino

Created by: Jess Rogerson (yelling commands at Claude.AI)

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