Building OnstepX Computerized GOTO system for Telescope

Build Your Own 'Go-To' Telescope: The Simple OnStepX System with FYSTEC E4

This guide is intended for astronomy enthusiasts who want to build a simple and affordable GOTO system for their telescope using the OnStepX firmware.

There are several ways to build an OnStepX controller, and many great resources already exist at the OnStepX Wiki.

⚠️ Note: I strongly recommend all users to read the official documentation before starting this build.

This specific build will provide you with a full-featured controller featuring:

RA (Right Ascension) and DEC (Declination) Motor Connectors
FOCUSER Connector
DEW HEATER port
USB Port for flashing and power
ON/OFF Switch with LED indicator

What is OnstepX?

OnStepX is an open-source, computerized telescope control system that adds GOTO and tracking capabilities to manual mounts using affordable microcontrollers.

It’s a DIY solution that allows you to control telescope mounts, focusers, and accessories — wirelessly — using smartphones, tablets, or computers. OnStepX is highly customizable, supports multiple mount types and is widely used in astrophotography setups.

Required Components

This build centers around the FYSTEC E4 Board for simplicity and low cost. Please gather the following parts before you begin:

Component	Quantity	Notes
FYSTEC E4 Board	1	Main controller
16mm Push Button Switch Latching 12V	1	For power switch
GX16 4Pin Aviation Connector 16MM	3	For RA, DEC, and focuser
5.5 x 2.1 mm DC Power Jack Socket	1	For power input
RCA Female Panel Mount Jack	1	For dew heater output
Dupont Jumper Wires	1	For jumper connection
24AWG/4 Shielded Wire (or similar)	As needed	For wiring
JST XH 4 Pin Connectors	3	For connections
M3 - .50 x 6-mm screws	8	For enclosure/board
FYSTEC E4 OnstepX Case*		STL files for 3D print
1 Inch Black Hook loop fastener	1	To attach the controller to mount

💡 Case Note for Printing:

1. The STL files mentioned here may not include a hole for the RCA Jack (Dew Heater port). You’ll need to either modify the 3D model before printing or drill a hole manually in the printed case before assembly.

2. The FYSTEC E4 board features a yellow LED. It is highly recommended to print the case in black (or a dark, opaque color) PLA or PETG filament to block this light.

The Build: Connections and Soldering

1. Preparing the FYSTEC E4 Board

⚠️ CRITICAL STEP: Before making any other connections, you must remove all factory shunts (jumpers) from the FYSTEC E4 board.

Next, you need to add a single jumper wire:

Connect the Z-Min pin to the TMC2209 stepper drivers (PDN).
Why? This allows OnStepX to properly configure and set up the stepper drivers.

2. Wiring the External Ports

Soldering is required for the three aviation connectors and the RCA jack.

If you prefer a solder-free approach, pre-soldered aviation connectors are available. However, an RCA jack may still require manual soldering.

💡 Tip: Look for “GX16-4Pin Male/Female Aviation Connector to 2.54mm XH Cable” kits to simplify wiring.

Note: At this time, this version of OnStepX does not include automatic dew-heater control, but this feature will be added in a future update.

Please refer the following diagram for all necessary connections.

Flashing the OnstepX firmware

Once your enclosure and connections are complete, the next step is to flash the firmware.

The Easiest Method: OnStep-Web-Tools

The simplest and most recommended way to flash the OnStepX firmware onto your FYSTEC E4 is by using Chad's OnStep-Web-Tools

Connect your newly built controller to your computer using a USB cable.
Navigate to the OnStep-Web-Tools website in your web browser.
Follow the online instructions to directly upload the firmware to your FYSTEC E4.

For other options, please visit Uploading Firmware (OnStepX / FYSETC E4)

If flashing is successful, you’ll see a new Wi-Fi network called “ONSTEPX”.
Default SSID: `ONSTEPX`
Default Password: `password`
Default IP Address: `192.168.0.1`
Once connected, you can access the web interface and adjust configuration settings for your specific mount type, axis settings, and motor steps.

For more details, see the official OnStepX documentation Uploading Firmware (OnStepX / FYSETC E4).

You've now built a powerful, flexible, and affordable computerized telescope controller! With OnStepX running on your FYSTEC E4, you are ready to explore the night sky with Go-To precision.

Enjoy your new system, and clear skies!