MaxESP4

For my OnStep telescope mount controller (visit my [group][1] for more information.)

This design is built around the ESP32S processor (available on eBay, Amazon, etc.) It has 4MB of flash, dual processor cores, runs at 240MHz, and has fast single precision capable floating point units.  This has a moderate amount of soldering necessary but most components needed to build one of these can be obtained from EasyEDA/LCSC and eBay.

**Note: 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. It's designed to support full control (microstep mode etc.) of FYSETC TMC2209 v3.1 drivers in all four sockets. It can also operate external GENERIC (Step/Dir/ENable signal) drivers for RA/Azm and Dec/Alt. All stepper motor connections are available on RJ jacks at the PCB back (screw terminals are optional.)
* WiFi or Ethernet: WeMos D1 Mini ESP8266 foot-print (uses Serial2.)
* Micro USB port built into the ESP32S.
* Status LED.
* 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 Serial0 port (shared with built in Micro USB,) 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.)

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Changes relative to MaxESP3:

General use of SMT components to keep soldering to a minimum as EasyEDA now makes this easy to order/low cost.

Design in favor of readily available TMC2209 drivers, they have the best performance/cost and minimize pin use.

WeMos D1 Mini socket now uses the alternate pin set (swapped location) for serial comms to the ESP32 so you can't flash an ESP8266 through the ESP32 in this design.

Now more features have dedicated pins:
* GPIO39 AUX7 was changed to RXTMC for TMC2209 UART drivers.
* GPIO12 EN12 was changed to STA for the buzzer/mini-speaker and status LED.
* GPIO14 CLK was changed to AUX3 (SPI isn't needed.)
* GPIO13 MOSI was changed to AUX4 for home sense (SPI isn't needed.)
* GPIO4 AUX2 was changed to TXTMC for TMC2209 UART drivers.
* GPIO5 CS2 was changed to EN enable for all axes (SPI isn't needed.)
* GPIO21 AUX3 was changed to I2C SDA only.
* GPIO22 AUX4 was changed to I2C SCL only.
* GPIO23 CS1 was changed to AUX7 for limit sense, PPS, etc. (SPI isn't needed.)

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History:
* Version 4.0 Initial Release

* Version 4.01 Encoder pullup was 5V now 3.3V

  [1]: https://groups.io/g/onstep