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This section explains how the OSSM PCB connects your ESP32-based controller to the motor driver. You can use the official OSSM PCB or create a DIY wiring setup.

Purchase OSSM PCB

Available pre-flashed from Research and Desire with the latest firmware, ready to use with your OSSM.

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Available Options

Official OSSM PCB

Reference board with 5V step/dir outputs, integrated protection, and standardized connectors for reliable operation.

DIY Wiring

Breadboard or custom harnesses for prototyping or using alternative motor drivers.

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Choosing Your Approach

The official OSSM PCB provides:
  • Pre-mapped GPIO to step/dir/enable
  • 3.3V-to-5V signal conversion for high‑speed, noise‑resistant control
  • JST‑PH connectors for tidy cable management
  • Built‑in power and back‑EMF protection
  • A design validated by the OSSM community
For most builders, the official PCB is the fastest and most reliable path to success.

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Key Considerations

Before you decide, keep these factors in mind:
ESP32 boards operate at 3.3V logic while many drivers use 5V inputs. Without proper level shifting, you may see:
  • Missed steps at higher speeds
  • Unreliable direction changes
  • Risk of damaging components
Verify input voltage requirements for your specific driver before wiring.
High‑speed step signals (up to 200 kHz) demand clean wiring:
  • Keep step and direction leads short
  • Route signals away from motor power cables
  • Use twisted pairs or shielded cable for runs longer than 30 cm
Size the driver supply for your motor:
  • Servo motors commonly use 24–48V DC
  • Stepper drivers vary by model (12–48V typical)
  • Power the ESP32 from USB or a regulated 5V rail, independent of motor power

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Official OSSM wiring

Use this section if you are wiring the OSSM PCB to the OSSM Gold Motor (57AIM series) or a compatible step/dir driver.
1

Gather parts

  • OSSM PCB
  • 24V power supply (UL‑certified recommended)
  • PH‑4 signal cable and green motor power connector (included with OSSM motor kits)
  • Appropriate motor and driver
For the OSSM Gold Motor wiring walkthrough, see Wiring your Gold Motor.
2

Connect motor power

  • Strip the red/black power leads.
  • Insert red (+) and black (–) into the two‑position motor power terminal on the PCB.
  • Tighten firmly to prevent intermittent connections.
Tug each wire gently. If it moves, retighten the terminal.
3

Connect step/dir signals

  • Plug the keyed PH‑4 signal cable into the PCB’s 4‑pin header.
  • Route the other end to the motor/driver control input as labeled.
The PCB outputs 5V, active‑low step/dir signals on the PH‑4 header, which improves noise immunity with many drivers.
4

Apply power and verify

  • Connect the 24V supply to the PCB’s 2.1 mm x 5.5 mm barrel jack.
  • Power on. The motor/driver should indicate power and be ready.
# Quick preflight
1) Power on the PCB
2) Confirm motor/driver status LED indicates power
3) Connect your controller and home the axis when mechanically assembled
If the remote is connected during bench testing, homing may not complete until the actuator is fully assembled on a rail.

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Alternative wiring configurations

If you are interfacing a different step/dir driver or prototyping on a breadboard:
1

Add a level shifter (required for 5V drivers)

Use a unidirectional 3.3V→5V level shifter for STEP, DIR, and ENABLE. Tie grounds between the ESP32, level shifter, and driver.
ESP32 (3.3V) → Level Shifter → Driver (5V)
     STEP  ────────────────→  STEP
     DIR   ────────────────→  DIR
     EN    ────────────────→  EN (if used)
     GND   ─────────────────  GND (common)
Do not drive a 5V input directly from an ESP32 pin.
2

Wire power correctly

  • Keep motor power separate from 5V logic rails.
  • Size supply wiring for current. Use 16–24 AWG on the PCB motor output terminals.
3

Validate signals

  • Start at a low step rate and increase gradually.
  • Confirm direction changes cleanly and that no steps are missed.

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Specifications

These specifications summarize the OSSM PCB capabilities.

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Power Input

ParameterValue
Voltage24V DC
Max current5A
Connector2.1 mm × 5.5 mm barrel jack
Use a high‑quality, UL‑certified power supply. Low‑quality supplies often fail to deliver rated power and can damage the motor or board.

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Signal Outputs

ParameterSpecification
Signal typeStep‑Dir
Logic level5V active low
ConnectorJST‑PH‑4

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Motor Power Output

ParameterSpecification
Voltage24V
Max current6A
Terminals2× screw terminals
Wire gauge16–24 AWG

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Back‑EMF Protection

The PCB includes built‑in protection against regenerative voltage spikes:
  • Inline diode to protect the power supply from reverse current
  • 1500 µF capacitor to handle regenerative energy

OSSM PCB spec sheet

Detailed electrical specifications and connector pinouts.

Wiring your Gold Motor

Step‑by‑step wiring for the OSSM Gold Motor (57AIM series).

Flash your OSSM

Use the web flasher to load firmware onto your board.