I built this to drive the stepper motor on a telescope mount. The requirement was for an accurate 12rpm that would make the telescope mount rotate to counter the earth’s rotation. The mount had a motor and gears installed but the commercial electronic ‘tracker’ was hugely more expensive than the system here. I tried to write the code in a way that could be easily modified for other speeds, and could be used as a starting point for more complicated systems. The ‘rpm = 12;’ line is right at the start so in many cases you will just need to change this number. It should work on most Ardunio boards. I started on a Uno and then went for a Nano for the final unit. It is set up for an Arduino with crystal frequency of 16Mhz and hence will need the timer pre-scaler code adjusting for other frequencies.

You will need:

· Arduino, e.g. Uno or Nano

· EasyDriver board

· Power supply – 4 AA batteries used here

· Stepper motor

The EasyDriver board takes a lot of hard work out of the Ardunio. It just needs two inputs – direction and step. It can be setup for single, half or ¼ or 1/8 microstepping with the latter being the default. It can drive up to 700ma per phase, up to 30v. I wanted the extra torque of the half step mode and hence set it up for this. Although designed for two bipolar windings it can also drive unipolar motors by ignoring the middle tap in each winding. In some cases the middle taps of the two windings are connected (as was the case here). If so this connection has to be removed. In this case it just required a cut in a track on the motor connection PCB.

Step 1: Connections


· On EasyDriver board – EN2 to GND (next to +5V) (to set half stepping)

· Positive supply to EasyDriver M+ PWR IN and wire from here to Vin on the Nano

· Negative supply to EasyDriver GND PWR IN

· Three wires from EasyDriver GND, STEP, DIR to the Arduino GND, D12 and D11 respectively.

Check using the wire colours and photos above.

I found that 6v was enough for the stepper motor. If you need to go higher check the voltage regulator chips on both boards to make sure they don’t get too hot.

<p>Awesome! Do you happen to have more information on the rest of your mount? I'd really like to use this driver as part of my Dob to equatorial tracking conversion.</p>
<p>I wish I could but I did this for a friend who lives some distance away and is not very well right now. I may be able to get more info in a few weeks time (if he gets a bit better). Sorry I am not an astronomer and so I would need more detail to understand what your requirement is. The principle of the mount was to point it at the North star and use the motor to counteract the rotation of the Earth. The way I got to the 12rpm requirement was by removing the motor, marking a line on the first gear and seeing how many turns this needed to turn the telescope by 10 minutes (graduated markings on the mount). I expected the requiremnt was going to be a round number. However the system here has pretty fine resolution (up to 1 in 65535) if you decide to specify the interrupt count directly (rather than via rpm setting) and runs in sync with the microcontroller crystal clock and hence should be both accurate and stable. Note also that you can add code to change the speed as a function of an input (e.g. potentiometer) if required. You could also add a display to indicate the speed. In another application I added a counter to the interrupt routine so I could keep track of position. As long as you can define your requirement you can probably program it. Mike</p>
<p>Great idea. Who is the stepper motor supplier or specs?</p>
<p>The stepper motor was one that had been in my 'will be useful sometime box' for a decade or so! It is a unipolar (4 coil, 5 or 6 lead). Most of these smaller motors are 48 step with the larger motors being 200 step. The individual coil resistance is 37ohms. The coils are in two connected pairs. I had to separate the mid coil connections as mentioned. I then drove the motor using the bipolar driver (EasyDriver) connected to the ends of the pairs of coils (no connection to mid point). The driver can handle a wide range of stepper motors. Just keep within the driver voltage and current specs.</p>
<p>My dad's entire garage is filled with &quot;Will be useful sometime stuff&quot;. hah! Loved that. :)</p>
<p>Well you can guarantee that the day you throw something away is the day before you find a great use for it.....</p>
<p>100% agree - ditched an old bathroom fixture last week - this week the parts would have been useful to fix the new leak :) </p>
<p>great little project btw! </p>
neat idea, Money saver too thanks

About This Instructable




Bio: Engineer, retired. Have always had an interest in electronics, often related to radio control. This evolved into a part time business that I still practice ... More »
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