Celestial tracker

Elelctronic device for controlling two motors coupled to eq5 mount for tracking celestial objects. It is not a GOTO positioner.

Similar projects worth following

Summary of Intentions

I have an equatorial mount (Bresser Exos-2 which is similar to EQ5 ) without any tracker or GOTO device. I enjoy looking for celestial objects by myself.

But handling the telescope becomes a bit hard on my back after several hours of stargazing on a freezing night. I would like to add a remote control to allow the telescope to be controlled in more comfortable body positions.

It would be a DIY version of these commercial solutions:

I would like to emphasize that I do not intend to do a GOTO, just put two engines to move the OTA remotely. In addition, we will add the possibility that once a celestial object is found, the telescope follows it without the need for user action. If you are looking for a GOTO project, I recommend these (they are excellent jobs):

Here it is presumed you are familiar with stargazing using telescope with equatorial mount.


  • Move the OTA in both dimentions of the celestial spehere
  • Vaiable speed by joystick
  • Tracking a celestial object in three speeds: sidereal,solar or lunar
  • Overheating, overcurrent alarm.


Power Requirements

If you have an observatory, I envy you. The usual thing is to use the telescope in the field, far away from any power outlets and therefore a battery is need. Reducing power consumption to extend the life of the battery charge is an essential requirement in this project. For it:

  • Since the speed requirement is not important in this case, we will use CMOS technology instead of TTL.
  • We will try to reduce the current throw the resistors (in pullups, pulldowns, voltage divider, etc.) to the minimum increasing their resistances to the maximum.
  • We will activate the “saving mode” (or “sleep mode”) in each of the ICs that have it. General speaking, we always chose the design alternative which implies less energy consumption.

Accuracy Requirements

When we action the joystick, we want the telescope moves in the correct direction and it is not necessary too much precision in the speed. We want the more the deflection the stick the faster the movement, and more near the central position slower motion must be produced. It does not matter if when the battery voltage falls the speed to become a little bit slower. Does not matter small changes in the speed produced by changes in the environment temperature neither. All these considerations apply when, I repeat, we are actioning the joystick, because we are not tracking any celestial object, we are only searching it, then no excessive precision is required.

But the thing changes in tracking mode. In this case we need the telescope follows the celestial object and keep it inside in the field of view as time as possible (it means always while it is visible). We must have in mind anybody could want this system for astrophotography. Therefore, for this mode it will be necessary to think in temperature compensation design. Although three screws will be provided for allowing the user to calibrate the system adjusting each tracking speed, the ideal thing would be that they must not be used for compensating external changes as temperature or falling voltage. We can accept the fine adjusts are used once or twice for year, maybe for compensating extreme differences of temperature between winter and summer or error given by the time equation. But after the system is calibrated, they should not be manipulated for a long time.

Why no Arduino?

That is good question and afraid I have not a good answer. Nowadays Arduino is a platform based...

Read more »


VCO emulation in microcap12

cir - 31.38 kB - 12/28/2020 at 16:53


  • 2 × Driver pulley 20 teeth. 5 mm bore
  • 2 × Driven pulley 60 teeth. 6 mm bore
  • 2 × Timing belt Wide 6 mm
  • 2 × Nema 17 stepper motors with a torque
  • 2 × Driver for stepper motor: DRV8825

View all 9 components

  • Correct diameter for inner hole of the shafts pulleys

    Alvaro Miguel12/28/2020 at 09:07 0 comments

    I was doubting if for my mount the proper bore of the pulleys were 6mm or 6,35mm, therefore I ordered both. I have recieved them and now I can tell you for Bresser Exos-2 the proper is bore is 6mm for two shafts (AR and Dec).

    Note this only apply for Bresser Exos-2.

  • Microsteps: good or bad?

    Alvaro Miguel12/22/2020 at 13:48 0 comments

    Last night, in a stargazing session for Jupiter-Saturn conjunction I talked with a astrophotographer. He is an expert about equatorial mounts, people ask for him modify then mechanisms of their mounts for improving them. I commented him about this project and his adviced me not use microsteps because somebody oneday told him they are bad. I hope that person is wrong. Have you heard something about that?

View all 2 project logs

Enjoy this project?



Similar Projects

Does this project spark your interest?

Become a member to follow this project and never miss any updates