arduino-motorfocus

Simple moonlite focuser protocol implementation for Arduino and stepper motors.

Tested with Arduino Nano and cheap 28BYJ-48 stepper motor with driver and INDI / Ekos. Works also with Pololu A4988 Stepper Motor Driver (see wiring).

Updated 3D/CAD models for TS 65/420 Quadruplet are available at Thingiverse: https://www.thingiverse.com/thing:2063325 Motor focuser for Starlight Feather Touch 2" by Cover1987: https://www.thingiverse.com/thing:3593910

Installation

Webupload via browser's Web Serial API

Only available for Chrome/Chromium at the moment. Visit https://fehlfarbe.github.io/arduino-motorfocus, connect your Arduino Nano and click the right button to upload the latest version :)

Install via PlatformIO

Download and install PlatformIO
Clone or download this project and unzip it
Open project with PlatformIO
Select the right config for your microcontroller e.g. nanoatmega328 for Arduino Nano with 28BYJ-48 stepper, promicro16 for Sparkfun Pro Mirco with 28BYJ-48 stepper or nanoatmega328_A988driver for Arduino Nano with A4988driver support in the bottom bar and upload to your Arduino (PlatformIO will download needed libraries automatically)

VSCode settings

Wiring

Wiring for 28BYJ-48 stepper motor with ULN2003A breakout board

28BYJ-48 wiring

Wiring for A4988 driver

Select config A4988driver in VSCode bottom bar (step 4). You can change the microstep resolution (full step, half step, ...) with MS1, MS2, MS3 pins on the driver board. See more at Pololu A4988 Stepper Motor Driver doc (Step (and microstep) size). If all pins are unconnected the driver will run in full step mode. Stepper with driver wiring

Wiring for in/out buttons

The internal pullups are active so you have to connect your buttons for manual focus to GND. The potentiometer is optional and can limit the maximum speed for manual focus. Buttons wiring

Wiring for temperature sensor DS18B20

You need a 4.7kΩ pullup resistor. If there is no sensor attached the temperatur will be zero. DS18B20 wiring

Troubleshooting

ASCOM driver cant find the focuser

Some people reported problems with arduino-motorfocus and Windows/ASCOM. If you use the ASCOM-Moonlite.DRO.Focuser driver the focuser doesn't appear in the setup list.

ASCOM driver cannot find focuser

This happens because the setup opens all COM ports, sends a command and waits for a proper response. Unfortunally Windows resets the device when the port is opened (DTR is set to low) and an Arduino clone needs a second or so to boot up so it won't receive the command and the setup gets a timeout. There are multiple ways to solve the problem:

You can flash the MiniCore Bootloader to your Arduino. This bootloader is faster and in my tests it was fast enough to get detected by the setup
Just install a 10µF or 33µF between RST and GND or remove the 100nF capacitor on the bottom of your Nano. You can see an image of the capacitor and further explanation on this website
Use a different Microcontroller like Arduino Pro Mini with an external USB-TTL converter and dont't connect the DTR line

And voilà the focuser will show up:

ASCOM setup finds focuser

ASCOM driver finds the focuser but can't connect

Same problem as above. Unfortunally the first solution, flashing the bootloader, didn't work for me but the additional capacitor between RST and GND works.

Other ASCOM errors

If there are different errors, please open an issue and attach the logfile. You can activate logging for you focuser in the properties setup:

ASCOM setup finds focuser

The logfile is located in %HOMEPATH%\Documents\ASCOM

You can also connect an USB-TTL converter to GPIO 10 to see all commands sent by your computer and some debug messages.

The motor moves very slow

Don't use a DEBUG build because SoftwareSerial printing slows down the microcontroller
Check the full/half/... microstep setup of your driver
Increase SPEED_MULTIPLICATOR and ACCELERATION in arduino-motorfocus.h

The motor doesn't move

Check wiring between microcontroller and your driver
Check if manual focusing via buttons is working
Check wiring between motor and driver, sometimes the motor coil cables are mixed up

PCB

I made a simple PCB that connects all the parts and supports Pololu style driver boards and ULN2003A breakout board. The KiCAD project and gerber files are located at hardware. PCB Populated PCB