Arduino Based ASCOM Rotator

One to many cloudy nights has spurred me into action. My imaging setup is getting closer to automated but I’ve had a distinct missing link, the ability to choose a guide star from within my astronomy applications. Since adding the MOAG and updating my guide camera I’ve added a Takahashi CAA rotator and it provides excellent manual rotation.

The reason I selected the CAA was price and aperture. I did look longingly at a number of electronic rotators.

Automation of the rotation was another issue. There seems to be lots automation for mounts and focuses but nothing for rotators. Google was not my friend. So I decided to write something. This is very much a work in progress but so far I have adapted the code from the SGL Automation guys and attempted to make it rotator specific. It supports ASCOM v6.

The ASCOM interface for rotators is reasonably simple, Move, Position, etc and the ASCOM documentation and templates are excellent. Well done standards guys, shame us health professionals can’t get our act together as we’ll as you have.

First go was to get the basics operating: Arduino, USB to serial driver, stepper motor, easy driver motor controller a couple of belts and a pulley. Check out the photos below.

I’ve only tested it with Maximdl using my bench setup as yet, but it seems to work well.

The bench setup.


The arduino (note the resistor is for the reed switch, keep reading).

The reed switch and magnet.


Reed switch and magnet.


I was having trouble this weekend determine the number of steps to make 360 degrees so I dug up an old reed switch, found a very small magnet and introduced homing and a step counter into the software, as of Sunday night it all appears to work.

The Arduino Project and VB in the solution - ES - works but its still a little messy to release, but here you are anyway.

Code in action below

Sample rotator screen shots with debug


Dew heater

My SCT fogs up most evenings. I’m a little reticent to use a hair dryer and not sufficiently rich to buy a proper dew heater, so I played around to make my own.

I dug out some nichrome wire, cut it to the length of the diameter of my scope (about 1m) and played around with voltages until I had a small increase in temperature (comfortably warm enough to hold onto with my fingers). It must only be a few degrees. Just be warned its VERY easy to fry you fingers so start with low voltages and work up.

I had a Jaycar kit MOSFET power supply hanging around, slight overkill I know. I dug up a relay I’d used for something else, added a DHT22, an LCD display along with an Arduino and behold!


The power supply is turned on by driving the relay. The Arduino code reads the DHT22 every 5 seconds, calculates the dew point temp, displays the current temp, the dew point temp and relative humidity. If the current temp is within 4 degrees of the dew point it turns on the power supply.

BTW the knob is only used to control the contrast on the LCD as it gets to bright when the scope is taking pictures.

Note the insulator on the nichrome as well. My scope conducts!


An now turned on