Wednesday, April 4, 2007

More on the focus control project

Last weekend I put together a couple of different stepper motor control kits to see how they each perform. The first was the CK1405 kit from Carl's Electronics. My assembled kit in it's testing configuration is shown below:

I really wanted the CK1404 kit but they do not carry it any more due to the UCN5804B chip being discontinued. But, I also ordered another kit from Alltronics. Their kit did not have much of a description but I took a chance on it anyway. As luck would have it, their kit included the UCN5804B stepper motor IC and much more versatility in features. Back to the original kit - I tested it out and just could not get satisfactory operation of the motor. It was very "choppy" and did not have much speed adjustment range. I put that one aside and moved on to the Alltronics kit, as shown below:

This kit worked very well. Motor operation was very smooth and there was a wide range of speed adjustment. Plus, this kit offers a low-speed mode, single-step function, half step mode, and a selectable full wave/2-phase drive. I decided to use the Alltronics kit for my design, which required some changes. Originally I intended to put everything in the hand-held case shown in my previous project post. But the Alltronics kit is too large to fit in that case. So the motor control kit will be mounted in a separate box at the mount. The hand-held case will just house the control switches and display.
This design got me thinking - can I control three different motors with one control board? Why not? I have three focusers, so it sure would be nice to control them all. What I am planning is a relay switching circuit that only switches on one motor at a time. There's no reason to ever control two focusers at the same time, so this should work. My hand control just needs three more switches, each one to enable one motor. Below is my basic schematic of the motor control circuit, without all the hand controls and display:

Also, over the weekend I built the display board, but have not yet tested it out:

It's getting closer! My mount comes back tomorrow, so the focus control project will probably be sidelined for a while until we have some cloudy weather.

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