Posted on Feb 6, 2014

This page is for info on converting the low resolution optical encoders, typically found in serial mice, into high resolution encoders needed for DSC`s (Digital Setting Circles), for your telescope, etc. The serial mouse encoders I found had the dpi stamped right in the side of the slotted disk 1, in my case 200 was stamped in the side.

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The mouse must be a serial type (like a logitech 3 button mouse), the type that plugs into the serial port. Do not use the common 2 mouse that plugs into the mouse port, they use continuous turn pots, not optical encoders. The serial mice have a serial interface for the optical encoders already and there isn`t any reason why you couldn`t reuse that portion of the circuit board as well if you needed to interface directly to your computer`s serial port. In my case I discarded that portion when I dissected mine with a jewelers saw as I didn`t need it. The program you use should somewhere ask for the resolution of the encoders and you can calculate an initial setting based on the dpi times the circumference of your bearing surface, if you attach the encoders like I did. Once you have them working, you test it by rotating the axis through a known number of degrees, preferably a full 360 and watch the readout on your program or digital setting circles to make sure it tracks properly. If there is a difference, simply adjust your final resolution to compensate and then retest. In case the dpi isn`t stamped in the side simply count the number of slots in the disk and multiply by four, then take a micrometer and measure the diameter of the little drive wheel on the encoder shaft and divide the previous calculation by (pi times the dia in inches) and it should give you the dpi. The result should come very close to a standard dpi. If I...

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