First of all, we wish to thank Mel Bartels, not only because his great software, but also for his continued support, through the scope-drive discussion list, to all the amateur astronomers trying to build and control his own scopes. Thanks, Mel!

 

NEW!: We are just working on a circuit based on the L298N IC which will sustancially simplify the system downsizing it, for systems up to 6A, 35v. You can find the basic circuit HERE, adapted for bipolar motors (this IC can also be used to drive unipolar steppers).

THE BASIS

This page shows an adapted circuit to command bipolar stepper motors using the nice software SCOPE by Mel Bartels. This was originally designed for working with the 5-6 pin "unipolar" steppers, which two wirings have a center tap. However, the bipolar steppers have only 4 pins. But the main difference between them, is that bipolar motors invert -reverse- the sense of the current on the wires instead of applying the voltage consecutively on every winding as unipolar motors do.
This kind of steppers -bipolar- can be found at some CG-5 & chinese clones mount motor kits. As I have purchased one of these recently, I was forced to find a solution to use Mel's software.
The following table could help you to understand the differences between UNIPOLAR and BIPOLAR working modes:

	unipolar steppers				bipolar steppers
1st step	+V	0	0	0	+V	-V	0	0
2nd step	0	+V	0	0	-V	+V	0	0
3rd step	0	0	+V	0	0	0	+V	-V
4th step	0	0	0	+V	0	0	-V	+V

THE DESIGN

 

the original circuit at Douglas W. Jones site

Working together with our astroclub "electrogenius", Carmelo, we tested a circuit of his own design, which worked pretty well. But it was not still able to manage the "microsteps mode" featured by Mel Bartels'. So, after some research around the WWW, we found the following circuit at Douglas W. Jones site, linked from Mel Bartels'.

As we were told by Mel at the drive-scope discussion list, there are a number of IC circuits for controlling this type of steppers, but we wanted to make a simple and "testeable" one, in order to measure the current, the different torque values at microstep/halfstep levels, and the overall behavior of the adaptation.

So, we designed the circuit in two ways: a completely new one, and a sort of "plug-in" to the original one for the people who want to obtain the kit, and then adapt it to their specific kind of steppers.

Having all this in mind, we made the new circuits, being necessary to use 4 blocks of the circuit shown above, to be able to control the altitude and azimuth steppers, RA and DEC in our case, 2 wirings each one.