- Introduction
- Why This Project?
- Disclaimer
- Features
- Hardware
- Firmware and Config.h Configuration
- Usage
- Optional Feature: GPS Integration
- Licensing
- Contribution & Support
- Contact
This repository contains the open-source hardware (OSH) design files (KiCad project) for a custom OnStep-JUWEI-17 controller board specifically tailored for the JUWEI-17 harmonic drive equatorial mount. This board provides a robust and configurable solution for upgrading the JUWEI-17 mount with the powerful OnStep firmware, enhancing its tracking accuracy and GoTo capabilities.
The circuit design is based on Roman Hujer's OnStep ESP32 Mini project, with specific adaptations for the JUWEI-17 mount — most notably, a hardware-controlled brake system.
This project addresses a critical issue for users in Japan (and possibly elsewhere):
The stock JUWEI-17 controller often includes a Wi-Fi/Bluetooth module that lacks Japan's Radio Law certification (技適マーク - Giteki Mark). Operating such a device is illegal in Japan.
This OnStep-JUWEI-17 project offers a compliant alternative, using certified ESP32 and ESP8266 (ESP-12F) modules that include Giteki certification.
The goal is to provide a legal, open, and high-performance upgrade path for the JUWEI-17 mount.
This project involves electronic assembly, including SMD components. Risks include, but are not limited to, electric shock, fire, damage, or injury.
This project is provided "as is", with no warranty.
Use at your own risk. While the board relies mostly on through-hole parts, experience with hand-soldering wide-pitch SMD components is strongly recommended.
- Based on Roman Hujer's OnStep ESP32 Mini, functionally similar to OnStep MAX ESP3
- Drop-in installation into the JUWEI-17 mount — no enclosure modifications required
- Hardware-Controlled Brake System: Uses the ENABLE signal from motor drivers — no firmware tweaks needed
- Open-Source Hardware: KiCad design files included
Custom PCB tailored for the JUWEI-17, based on the OnStep ESP32 Mini reference.
Operates on 12V DC, supporting the original brake solenoid and motor drivers.
Refer to the ASSEMBLY_GUIDE.md for detailed component list and assembly instructions.
The complete set of Gerber and drill files required for PCB manufacturing can be found in the KiCad/gerber/ directory. These files are ready for submission to a PCB fabrication service.
Location: KiCad/gerber/
Here are some visual references for the project.
Uses standard OnStep firmware.
Circuitry is nearly identical to the OnStep ESP32 Mini (minus the brake circuit), so you should reference that project for pin definitions and configurations.
The pin map settings for this board are a modification of the standard Pins.MaxESP3.h file. They mirror the specific assignments documented by the OnStep ESP32 Mini project on OSHWLab.
For your reference, the following assignments are replicated on this board:
- Aux7 = 36
- OneWirePin = 15
- ReticlePin = 19
- TonePin = 2
- PecPin = 39
- AnalogPecPin = A3
Variable names may differ in newer firmware.
You will need to adapt these pin definitions to the appropriate structure in your version of Config.h and the corresponding Pins.*.h files.
In Config.h, the gear ratio and motor settings must be exact. Errors will affect tracking and GoTo precision.
The JUWEI-17 mount is typically advertised with a gear system consisting of a 1:100 harmonic drive and a 1:4 pulley, for a total reduction of 400:1. The motors are standard NEMA17, with a 1.8°/step resolution.
However, based on user-reported data, the actual gear ratio appears to be 404:1, not 400:1.
From Cloudy Nights post:
- JUWEI original firmware uses 3591.111 steps/degree
- Formula: (200 steps/rev × 16 microsteps × 101 x 4) ÷ 360 = 3591.111...
Harmonic drives can have ±1 variation depending on which spline is fixed.
Measure your actual gear ratio to ensure accuracy — do not trust online listings.
- Ensure all pin/motor settings in Config.h and Pins.*.h match your board
- Always re-upload firmware after making changes
The following motor driver modules have been successfully tested and confirmed to work with this board. The values in quotes ("...") are the corresponding AXIS?_DRIVER_MODEL settings in Config.h.
- BigTreeTech TMC2130 V3.0: "TMC2130"
- DRV8825 (Brand Unknown): "DRV8825"
- TMC2209 Module included with JUWEI-17 (Legacy Tested): "TMC2209S"
Note: All drivers were tested with 16 microsteps, which is the same setting as the original mount.
To build and install this controller, follow the detailed instructions in ASSEMBLY_GUIDE.md.
A user successfully implemented full GPS functionality by creatively repurposing existing pins on the AUX header and defining a Software Serial interface in OnStepX.
- This method utilizes pins otherwise designated for PEC and the Reticle light:
- PPS Signal (Time Sync): Connect the GPS PPS (Pulse Per Second) output to the PEC Input (IO39).
- RX Data (Serial Data): Connect the GPS TX output (data) to the Reticle Pin (IO19).
- Critical Note: To ensure a clean signal path for the GPS, you must omit R20 and remove C7 during board assembly.
The GPS functionality must be enabled by defining the appropriate Software Serial pins within the OnStepX configuration file (Config.h).
This design is derived from the OnStep ESP32 Mini project and is licensed under GPLv3.
✳️ Note: Although GPLv3 is suitable for firmware, open hardware often benefits from dedicated licenses like the TAPR Open Hardware License (OHL). These better address physical product concerns such as patents and manufacturing rights.
Contributions welcome!
You can:
- Report bugs via GitHub Issues
- Submit Pull Requests
- Join discussion on Cloudy Nights forum