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.
Purchase OSSM PCB
Available pre-flashed from Research and Desire with the latest firmware, ready to use with your OSSM.
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.
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 for the official OSSM configuration
For most builders, the official PCB is the fastest and most reliable path to success.
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
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.
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
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.
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 physical assembly and wiring, use the official wiring stage.
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.
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.
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 assembledIf the remote is connected during bench testing, homing may not complete until the actuator is fully assembled on a rail.
Alternative wiring configurations
If you are interfacing a different step/dir driver or prototyping on a breadboard:
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.
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.
Validate signals
- Start at a low step rate and increase gradually.
- Confirm direction changes cleanly and that no steps are missed.
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 |
Use a high‑quality, UL‑certified power supply. Low‑quality supplies often fail to deliver rated power and can damage the motor or board.
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