> ## Documentation Index
> Fetch the complete documentation index at: https://docs.researchanddesire.com/llms.txt
> Use this file to discover all available pages before exploring further.

# PCB Overview

> Introduction to the OSSM printed circuit board designs and wiring options

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.

<Card title="Purchase OSSM PCB" icon="cart-shopping" href="https://www.researchanddesire.com/products/ossm-reference-board">
  Available pre-flashed from Research and Desire with the latest firmware, ready to use with your OSSM.
</Card>

## Available Options

<CardGroup cols={2}>
  <Card title="Official OSSM PCB" icon="microchip" href="#official-ossm-wiring">
    Reference board with 5V step/dir outputs, integrated protection, and standardized connectors for reliable operation.
  </Card>

  <Card title="DIY Wiring" icon="plug" href="#alternative-wiring-configurations">
    Breadboard or custom harnesses for prototyping or using alternative motor drivers.
  </Card>
</CardGroup>

## Choosing Your Approach

<Tabs>
  <Tab title="Official PCB">
    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

    <Tip>
      For most builders, the official PCB is the fastest and most reliable path to success.
    </Tip>
  </Tab>

  <Tab title="DIY Wiring">
    Choose DIY wiring if you:

    * Want to prototype before committing to a PCB
    * Need to interface with a non‑standard driver
    * Already have compatible parts on hand
    * Prefer to learn the system at the signal level

    <Warning>
      An ESP32 uses 3.3V logic. Many motor drivers expect 5V step/dir signals. Always include a level shifter when wiring directly from an ESP32 to a 5V driver.
    </Warning>
  </Tab>
</Tabs>

## Key Considerations

Before you decide, keep these factors in mind:

<AccordionGroup>
  <Accordion title="Voltage level compatibility">
    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.
  </Accordion>

  <Accordion title="Signal integrity">
    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
  </Accordion>

  <Accordion title="Power supply requirements">
    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
  </Accordion>
</AccordionGroup>

## 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.

<Steps>
  <Step title="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

    <Note>
      For the OSSM Gold Motor wiring walkthrough, see <a href="/open-source-sex-machine/ossm-electronics/wiring-your-gold-motor">Wiring your Gold Motor</a>.
    </Note>
  </Step>

  <Step title="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.

    <Check>
      Tug each wire gently. If it moves, retighten the terminal.
    </Check>
  </Step>

  <Step title="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.

    <Tip>
      The PCB outputs 5V, active‑low step/dir signals on the PH‑4 header, which improves noise immunity with many drivers.
    </Tip>
  </Step>

  <Step title="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.

    ```bash theme={null}
    # 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
    ```

    <Check>
      If the remote is connected during bench testing, homing may not complete until the actuator is fully assembled on a rail.
    </Check>
  </Step>
</Steps>

## Alternative wiring configurations

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

<Steps>
  <Step title="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.

    ```text theme={null}
    ESP32 (3.3V) → Level Shifter → Driver (5V)
         STEP  ────────────────→  STEP
         DIR   ────────────────→  DIR
         EN    ────────────────→  EN (if used)
         GND   ─────────────────  GND (common)
    ```

    <Warning>
      Do not drive a 5V input directly from an ESP32 pin.
    </Warning>
  </Step>

  <Step title="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.
  </Step>

  <Step title="Validate signals">
    * Start at a low step rate and increase gradually.
    * Confirm direction changes cleanly and that no steps are missed.
  </Step>
</Steps>

## Specifications

These specifications summarize the OSSM PCB capabilities.

### Power Input

| Parameter   | Value                       |
| ----------- | --------------------------- |
| Voltage     | 24V DC                      |
| Max current | 5A                          |
| Connector   | 2.1 mm × 5.5 mm barrel jack |

<Warning>
  Use a high‑quality, UL‑certified power supply. Low‑quality supplies often fail to deliver rated power and can damage the motor or board.
</Warning>

### Signal Outputs

| Parameter   | Specification |
| ----------- | ------------- |
| Signal type | Step‑Dir      |
| Logic level | 5V active low |
| Connector   | JST‑PH‑4      |

### Motor Power Output

| Parameter   | Specification      |
| ----------- | ------------------ |
| Voltage     | 24V                |
| Max current | 6A                 |
| Terminals   | 2× screw terminals |
| Wire gauge  | 16–24 AWG          |

### 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

## Related guides

<CardGroup cols={2}>
  <Card title="OSSM PCB spec sheet" icon="file" href="/open-source-sex-machine/ossm-electronics/ossm-pcb-spec-sheet">
    Detailed electrical specifications and connector pinouts.
  </Card>

  <Card title="Wiring your Gold Motor" icon="bolt" href="/open-source-sex-machine/ossm-electronics/wiring-your-gold-motor">
    Step‑by‑step wiring for the OSSM Gold Motor (57AIM series).
  </Card>

  <Card title="Flash your OSSM" icon="cpu" href="/open-source-sex-machine/flashing-your-ossm">
    Use the web flasher to load firmware onto your board.
  </Card>
</CardGroup>