For my OnStep telescope mount controller (visit my [group][1] for more information.) This design is built around an onboard STM32F411CE processor. It has 512KB of flash, runs at 100MHz, and has a floating point unit for well rounded performance. All I/O leaving the PCB has ESD protection. All power outputs are fused (500mA, self recovery type.) This is one of the easiest OnStep controllers to build, requiring only a modest amount of soldering. **Note: This design is for non-commercial use only (see License terms, CC-BY-NC-SA 3.0)** This controller includes the following features: * Power: Coaxial power jack, fuse, and power switch connection. * Stepper drivers: Four, one for RA/Azm, one for Dec/Alt, one for a focuser, and one for a rotator/second focuser. They all share a common SPI bus for use with SSS TMC2130 and TMC5160 stepper drivers only. All stepper motor connections are available on RJ jacks at the PCB back (screw terminals are optional.) * EEPROM M24C64: between 2x and 8x larger than other platforms (8KB) and higher endurance, Built-in. * DS3231 RTC: Built-in. * WiFi or Ethernet: WeMos D1 Mini ESP8266 foot-print (uses Serial2.) Note that WiFi can't be flashed through the STM32F411 (you must pull the WeMos D1 Mini and plug into USB) due to software issues though the design supports it in theory. * USB port. * Mini speaker for alert buzzer. * DB15 15 pin D-Sub connector: primary external I/O for Gnd, +3.3V, 5V, two Home Switches, PEC, PPS, I2C, the Serial1 port, and two channels of A/B encoder inputs. * 3.5mm stereo mini jack: secondary external I/O for Limit Switches and Reticle. * RJ12 Modular connector: ST4 guider interface (with optional 5V power.) [1]: https://groups.io/g/onstep History - Version3.6 - First release - Version3.61 - PPS was moved from Aux0 to Aux2 affording more flexibility. WeMos D1Mini reset/fw upload circuitry was removed. Added pulldown resistors for the CLK/DSO pins of TMC5160's.