The PiBot Controller V5.88 Ultra is a high-performance 6-axis CNC controller based on the ESP32-S3-WROOM-1U-N8R8 module, compatible with both FluidNC and grblHAL firmware. Its core design philosophy is flexibility — it provides both on-board plug-in stepper driver sockets and external driver connectors simultaneously, allowing users to freely choose their drive solution based on actual needs. From entry-level A4988 modules to high-end TMC5160 SPI drivers, one board covers it all.

The controller features a 4-layer PCB design, fully optocoupled inputs, isolated RS485 communication, and an independent motor power rail. It is suitable for CNC routers, laser cutters, CNC mills, plasma cutters, and other types of CNC machines.

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• ESP32-S3-WROOM-1U-N8R8 — Dual-core LX7, 8MB Flash + 8MB PSRAM, external IPEX antenna connector
• Dual USB-C ports — Primary USB via CP2102 chip for reliable serial communication; secondary USB via native ESP32-S3 CDC interface, with future USB Host expansion support (gamepads, jog controllers, etc.)
• WiFi / Bluetooth — Supports FluidNC WebUI for wireless control from PC, phone, or tablet
• Isolated RS485 — ADUM3201 digital isolator + B0505XT isolated DC-DC supply + SN65HVD3082 transceiver, fully galvanically isolated for VFD spindle control via Modbus RTU
• RJ12 Expansion Port — Standard UART interface, compatible with pendants and display modules

The standout feature of the V5.88 Ultra is its on-board driver + external driver dual-mode coexistence. All 6 axes provide both interface types simultaneously:

• Standard Pololu 16-pin sockets, compatible with all popular driver modules: A4988, DRV8825, TMC2208, TMC2209, TMC2130, TMC5160, etc.
• Direct SPI bus routing — Individual CS (chip select) signal per axis (XCS/YCS/ZCS/ACS/BCS/CCS), shared SDI/SCK/SDO lines. TMC2130/TMC5160 SPI mode works out of the box with full StallGuard, CoolStep, and StealthChop support — no extra wiring needed
• Selectable VDD voltage — VDDSEL jumper to choose +5V or +3.3V driver logic voltage
• SLEEP / RESET jumpers — Configurable sleep and reset behavior for driver modules
• Per-axis Step / Dir / Enable status LEDs

• 6+1 sets of 4-pin JST-XH connectors, each providing: Step, Dir, Enable, GND
• Signals output via 3× 74AHCT595 I2S shift registers at 5V level, capable of directly driving the optocoupler inputs on industrial external stepper drivers
• Supports FluidNC I2S_STATIC / I2S_STREAM stepping engines

• Independent VMOT power input, separated from the control logic supply
• 6× 100µF bulk electrolytic capacitors (CG1–CG6) for adequate power filtering and decoupling

• (10) Fully optocoupled inputs (TLP521 optocouplers) — For limit switches, probes, e-stop, door interlock, etc.
• Each input has a dedicated LED status indicator for easy wiring diagnostics
• Selectable Switch VCC — SWVSEL jumper to choose Vin or +5V as switch power
• Compatible with NPN proximity sensors and standard mechanical switches
• TVS protection (PSM712) against ESD and surge damage

• 4× 5V digital/PWM outputs via 74AHCT125 buffer
• Suitable for PWM spindle speed control, laser power control, enable signals, direction signals, etc.

• 2× N-channel MOSFETs (NCE6005AR) for relays, solenoids, coolant pumps, and other inductive loads
• On-board flyback diodes (B340A) for safe inductive load driving
• MOSFET power rail connected directly to VMOT

• LM358 op-amp based DAC circuit, outputting 0–10V analog voltage
• On-board 20kΩ precision trim pot for adjusting maximum output voltage
• Optocoupled forward/reverse direction signals (OPT1/OPT2), common ground referenced from VFD side

• Input Voltage: 12V–24V DC via screw terminal
• Main buck converter: TPS54360 synchronous step-down converter, wide input range, high efficiency, providing +5V main power rail
• Isolated supply: B0505XT-1WR3 isolated DC-DC, providing independent +5V_ISO / GND_ISO for the RS485 section
• 3.3V LDO: Powers the ESP32 and logic circuitry
• Reverse polarity protection: B560C Schottky diode prevents damage from reversed power connections
• USB power management: MIC2005A load switch with fault protection — USB cannot back-power the controller

• Micro SD card — SPI interface for G-code file storage and configuration files
• CNC I/O Module Socket — Compatible with standard FluidNC I/O expansion modules for adding relays, extra inputs/outputs, MOSFETs, etc.
• OLED Display Header (J4, 4-pin) — GND, 3V3, IO25, IO27 via I²C, supports SSD1306 and other common OLED displays
• SPI signal output header — Exposes SPI bus directly for connecting additional SPI peripherals

• 4-layer PCB — Dedicated power and ground planes for improved power integrity and EMI performance
• Board size: Approximately 160mm × 100mm
• Four corner mounting holes — Standard spacing for common enclosure mounting
• Extensive status LEDs — Power indicator, per-axis Step/Dir/Enable status, MOSFET status, RS485 TX/RX indicators, input states
• Boot / Reset buttons — On-board buttons for firmware flashing without jumper wires

Firmware is uploaded via the USB-UART port or the FluidNC Web Installer. Configuration is done by editing a YAML text file and uploading it to the ESP32's Flash storage.

Standard Pololu 16-pin layout:

Pin 1:  EN          Pin 16: VMOT
Pin 2:  MS1/SDI     Pin 15: GND
Pin 3:  MS2/SCK     Pin 14: 2B
Pin 4:  MS3/CS      Pin 13: 2A
Pin 5:  RST/SDO     Pin 12: 1A
Pin 6:  SLP         Pin 11: 1B
Pin 7:  STEP        Pin 10: VDD
Pin 8:  DIR         Pin 9:  GND

In SPI mode: MS1→SDI (MOSI), MS2→SCK, MS3→CS (individual per axis), RST→SDO (MISO).

4-pin XH2.54 (one set per axis):

Pin 1: Enable
Pin 2: Step
Pin 3: Direction
Pin 4: GND

3-pin JST-XH (one set per input):

Pin 1: Switch VCC (Vin or +5V, jumper selectable)
Pin 2: Signal (optocoupler input)
Pin 3: GND

A basic FluidNC YAML configuration template using the on-board driver sockets:

board: PiBot V5.88 Ultra
name: PiBot Ultra 6-Axis

stepping:
  engine: I2S_STATIC
  idle_ms: 254
  pulse_us: 4
  dir_delay_us: 1
  disable_delay_us: 0

i2so:
  bck_pin: gpio.16
  data_pin: gpio.17
  ws_pin: gpio.18

spi:
  miso_pin: gpio.13
  mosi_pin: gpio.11
  sck_pin: gpio.12

sdcard:
  card_detect_pin: NO_PIN
  cs_pin: gpio.10

xyzabc-6600-config.yaml

tmc-config.yaml

Download Schematic PDF

Version: V5.88, Date: 2026-04-27

• PiBot Official Website
• FluidNC Firmware (GitHub)
• FluidNC Wiki
• FluidNC Web Installer