Posted on Feb 6, 2014

Make an electronic focuser to help with the astro-photography. The electronic focuser project allows accurate focussing under computer control. This is most useful for eyepiece projection astro-photography where I found that touching the focuser was enough to knock the object from view, because of the higher magnification factors involved. The stepper motor for

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the focuser is controlled by the DSC project board, using spare control lines on the ports. These controls allow the stepper motor to be enabled/disabled and moved in either direction at a rate determined by the software. These control lines are connected to a dedicated stepper motor interface IC to simplify the circuit. The stepper motor for the focuser was purchased from Farnell Components part no 7134423. The motor has a step count of 200 for 360 degrees of rotation which equates to 1. 8 degrees of rotation per step. Check out the data sheet. The motor is configured in unipolar mode, which means that four of the eight wires are connected to the +12V supply, and brings the number of wires between the focuser and the interface down to five. The bracket itself was made from a piece of aluminium I had lying around and it was simply cut it to size and shaped. The original focuser was first stripped down and thoroughly cleaned as the grease used was of a very `sticky` type. I then used normal grease instead which made the mechanism much smoother to use. Next the aluminium was made to size and holes drilled to allow it to be bolted on to the focuser. The stepper motor was then fitted and marks made on the aluminium for the motor screws. After these holes were drilled, the position of the five pin DIN socket was marked out and cut. Finally the whole thing was assembled and the wires soldered from the stepper motor to the five...

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