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The MiniPCB Version 2

If you are looking for information on an earlier version of the MiniPCB that page can be found here.  This earlier version is still useful and recommended when you need to build the controller into a mount.

The image below shows an OnStep built on a MiniPCB Version 2 (scroll down to see the bill-of-material.) This PCB is designed to fit inside a commonly available aluminum case.   Though the case flat end caps will need very careful need drilling, cutting, and filing to provide openings for the various connectors.  If a 3D printer is available plastic end caps can be printed with little time or effort.  This is the case the MiniPCB Version 2 is designed to fit: Aluminum Enclosure Electronic DIY PCB Instrument Project Box Case(100x71x26mm)

An alternate 3D printed case was designed by Roman Hujer. It uses a Pi-Fan for cooling, rather than an aluminum case.

The very affordable EasyEDA service can be used to order this version of the PCB (or obtain the Gerbers.)


  • Goals: This controller was designed to be a compact and elegant basic goto controller.  The specified components are of very good quality wherever possible, reliability rather than absolute lowest cost was the objective.
  • Performance: The MiniPCB2 supports the Teensy3.2 and Teensy4.0 micro-controllers.  The Teensy4.0 is far faster than any other OnStep supported MCU.
  • Non-volatile memory/EEPROM: Built-in, no external device required.  The Teensy3.2 has 2KB.  The Teensy4.0 has 4KB which is nice for user catalog storage.
  • Easier OnStep firmware upload/update compared to other options with a simple to configure software environment and an upload that doesn't require physical access to the controller.
  • Easier WiFi firmware upload/update, the WeMos D1 Mini ESP8266 has a builtin micro-usb to plug into (just unplug it from the PCB first!)
  • Easier to solder with a minimum of solder points compared to other options.
  • Back connections:
    • 1/8" mini stereo jack for the PEC sensor.
    • Two RJ45 8-pin jacks for the RA/Dec or Alt/Azm stepper motors.
      • Optionally use AMP 1776275-4 screw terminals instead for better reliability & current handling.  One of these days I'll get around to designing a screw down wire clamping back cover.
    • 1/8" mini stereo jack for Limit Sense and illuminated Reticle connections.
      • These connectors can serve other purposes like feature control instead of their primary function (you may need to omit a capacitor for this.)
  • Front connections:
    • Teensy3.2/4.0 micro-usb which provides a USB interface (for connection from a PC.)
    • Industry standard RJ12 jack ST4 interface with optional 5V power on pin 1.  This supports the SHC.
    • Coaxial DC power jack, 24V 5A rated.


Whatever you build use an appropriate DC rated fuse (current rating depends on stepper drivers/motors/etc.)