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The HomeBrew Gen3 (HBG3) Accessory for Celestron Mounts

This third-generation (Gen3) design, for interfacing to the AUX bus of a Celestron computerized telescope mount, is known as the "HomeBrew Gen3", or "HBG3" for short. It is the culmination of three years of experimentation and earlier attempts. The Gen3 hardware uses active 5V TTL drive with current-limiting resistors to make it 100% electrically safe -- safer and more compatible than some of Celestron's own products! This design works with any Celestron telescope mount that has an AUX port, even the ancient Nexstar GPS mount.

The basic HBG3 is a combination of a custom Printed Circuit Board (PCB), and a 30-Pin ESP32 DevKit-v1 module running special firmware, along with various switches and connectors etc. It is intended as a DIY project (more on this below). The PCBs are available from the author -- see below.

See the HomeBrew Gen3 thread on CloudyNights for development and discussion of the design.

HomeBrew Gen3 (HBG3) accessory for Celestron Telescopes.

What Is It?

The HBG3 is a small electronic accessory that connects to an AUX (or hand-controller) port of a Celestron Telescope mount. It provides multiple ways for computers, smartphones, and tablets to connect to and control the mount with CPWI, SkyPortal, or SkySafari+/Pro software:

  • 802.11n 2.4GHz WiFi, compatible with any software that understands "Celestron WiFi" as a connection method, including CPWI, SkyPortal, and SkySafari+ or SkySafari-Pro. Functionality is a superset of that provided by Celestron's own third-generation SkyPortal/SkyQLink WiFi adapters, and a mechanical switch is used to select between what Celestron calls "Direct Connect" (server), and "Access Point" (client) modes of operation.
  • Bluetooth Classic, which connects with SkyPortal/SkySafari on an Android device through the assistance of a 3rd-party Android app to bridge the connection from Bluetooth to TCP/IP. This then appears to the apps as "Celestron WiFi" in "Access Point" mode. Click here for detailed information on using Android Bluetooth. Bluetooth tends to be more reliable than WiFi, because of lower bandwidth and better tolerance of device power-saving mechanisms. Apple chose not to support Bluetooth Classic on the iPhone/iPad, so this is an Android-only thing. CPWI on a PC can also connect to Bluetooth as if it were a "Serial" or "USB" connection.
  • Direct wired USB, aka. "PC-Port" or "Mount-USB" (or "MUSB"), giving CPWI and other software a solid connection to the mount without the interference issues that can arise with 2.4GHz wireless connections. A mechanical switch is used to select this mode of operation. The computer's operating system must have device drivers installed for the Silicon Labs CP210x USB-Serial adapters (more on this below).
  • Unlike other third-party (eg. SkyFi) modules, the HBG3 does not connect through a hand-controller, and does not require a separate power supply or battery. It instead plugs directly into the mount, and is powered by the mount, just like Celestron's own accessories. It draws very little power though, so no worries about that!


    What Else Can It Do?

    The HBG3 has a plethora of other useful capabilities, including GPS ("SkySync"), a Nunchuck (thumbstick) interface, OLED display, Smart 2X DewHeater controller, Focus-Motor emulation and control, wireless Nexstar+ hand-controller, workarounds for Celestron bugs, etc.


    Blue swith (USB/RF-Kill); Red switch (WiFi mode).

    Where Do I Get One?

    The HomeBrew Gen3 is intended as a DIY project, and the schematic and Open Source source code (click to download) are freely available.

    The PCB can be obtained by emailing the author. Kits and pre-assembled units are also sometimes available.

    Acquiring the mostly pre-wired PCB with pre-soldered SMDs is recommended, and makes the job a lot simpler and less error-prone. The remaining assembly steps mainly involve simple through-hole soldering.

    Whichever way, it will still involve some DIY. One must do some research by reading everything about it on this site, and browsing the HomeBrew Gen3 thread at CloudyNights for more detail.

    The assembly pictorial has been updated, now showing the latest PCB, OLED display, and GPS module.
    Here is a new pictorial showing the extra steps to assemble an HBG3-Relay.
    An updated parts list can be found here.


    What Are The Red/Blue Switches For?

    There are normally two tiny slider switches on the HBG3, with the left side one coloured Blue, and the right side one coloured Red.

    The Blue switch should be down, closest to the PCB, for normal operation. When it is up, away from the PCB, this selects Mount-USB (MUSB) mode and also turns off WiFi and Bluetooth.

    The Red switch is used to select between the two WiFi modes. Down means "direct connect mode", where the HBG3 acts as a SoftAP or WiFi Server. Up means "access point mode", where the HBG3 will become a client of some other existing WiFi network, after first configuring the SSID/passkey for such using one of the apps.


    How To Install/Update The Firmware?

    If your HBG3 has v8.1 or newer firmware already, there is now a built-in OTA Firmware Updater. This can be accessed from the OLED display, or from the serial/debug monitor with the "ota_update" command. No need to install anything else to perform firmware updates! For this to work, the HBG3 needs internet access using "Access Point" mode for WiFi. See here for WiFi instructions. Unlike Celestron's updates, updating the HBG3 firmware is safe and cannot result in a "bricked" unit.

    Otherwise, a complete self-contained build system for building/uploading the firmware from source code is also available:
    HBG3_Arduino_Linux64.tgz (Linux64, 638MBytes).
    HBG3_Arduino.zip (MS-Windows, 659MBytes).
    Both of the above include source code for all versions of the HBG3 firmware.

    Instructions for using the HBG3_Arduino packages:

    Download the above HBG3_Arduino archive to your machine. Linux users can quickly untar it, but MS-Windows users will need to use 7zip (or the MUCH SLOWER built-in unzip of MS-Windows) to unzip it to a Desktop folder called HBG3_Arduino.

    MS-Windows users will need to install (only once, ever) the included Serial Port driver from the CP210x_Universal_Windows_Driver sub-folder: Right-click on the silabser.inf file, and click INSTALL. You should now be able to connect the HomeBrew USB to the PC and see it be assigned a COM port.

    Now run the arduino.exe program from the HBG3_Arduino folder. The Arduino IDE will then start up. From it's File menu, select Sketchbook, and then the version of Firmware that you want, eg. hbg3_v8.46. A new window will pop open with the HBG3 source code shown. Close the old/original window now.

    Under the Tools menu, select the appropriate COM port for your connected HBG3. Now click on the UPLOAD button near top left. The system should automatically build the code and send it to your HBG3. If uploading fails before 100%, just click it again to retry. Done.

    An alternative method for updating from firmware older than v8.1 on MS-Windows, might be to install/use the ESP32 binary flasher.

    Speaking of the firmware, click here for a near-complete version history.


    Recent revision of the HBG3 PCB
    HBG3 with GPS+OLED HBG3 with GPS+OLED HBG3 with GPS+OLED
    HomeBrew Gen3 side2 Newest revision of the HBG3-Relay PCB HBG3-Relay HBG3-Relay Three generations of Relay PCBs

    HBG3 Standalone Focus Motor Controller with 12V feed-through power and red Nunchuck

    HBG3 Standalone Focus Motor Controller with 12V feed-through power and red Nunchuck.