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The MaxSTM Version 3.6 (SMT)

The image below shows OnStep telescope controllers built on the MaxSTM Version 3.6 SMT PCB.  This board uses either the STM32F411CE at 100MHz or STM32F401CC at 84MHz, you can see a comparison of hardware features here.  The PCB is designed to fit inside this Aluminum Enclosure Electronic DIY PCB Instrument Project Box Case (120x97x40mm) to facilitate a complete professional looking solution.  There are 3D printable panels to fit the above enclosure in the group files section.

The MaxSTM features:

  • Easy to assemble into a finished controller with minimal soldering.
  • An onboard STM32F411CE or STM32F401CC micro-controller has plenty of RAM and flash memory resources (including 8KB of high write endurance EEPROM) for this application.  It also has a floating point unit for fast alignment model calculations.  This micro-controller's performance is in the same general class as the ESP32, that is, it's fast enough for OnStep in almost any use case.
  • WeMos D1 Mini Pro for WiFi.
  • DS3231 RTC.
  • Rugged full sized USB port.
  • ST4 port with SHC support.
  • DB15 connector with support for adding:
    • Incremental quadrature (A/B) encoders.
    • BME280 ambient conditions sensor.
    • 2 dew heaters and 2 switches (some are setup as 1-Wire devices.)
    • DS18B20's for spot temperature; focuser TCF, etc.
    • A spare serial port.
  • 1/8" stereo mini jack has the limit sense input and a variable brightness illuminated reticle output.
  • Both RJ45 (for Ethernet patch cords) and screw-down terminals are allowed for stepper motor outputs (pick one or the other.)
  • Power jack.
  • Optional power switch.

Below is a fully assembled MaxSTM3.6 for reference.