1. Opto-Isolator Switch
The
tracker was originaly designed with in built opto-isolators to protect/isolate
the computer electronics from the external tracker circuitry.This simplified
the control circuitry when using the Parallel Port of a PC. These isolators
were for the N, S, E & W commands used primarily for autoguiding.
Modern laptops do not have a Parallel Port and rely mainly on USB interfaces. A USB to telescope interface adaptor is produced by Shoestring Astronomy, called a GPUSB. The GPUSB has inbuilt opto-isolators, so I needed to add a switch to deselect the internal tracker ones when a GPUSB was used. The image opposite shows the four white opto-isolators on the left hand side and the blue four pole switch. The switch slider is accessed through a slot on the bottom of the external cover.
2. Worm Shaft Tensioner External Adjuster
The
worm shaft has a spring loaded tensioner which applies
a lateral force to keep the worm mated with the worm gear.
The load is adjusted via a knurled thumbscrew. This could
only be adjusted with the main cover removed.
To enable the tension to adjusted externally, I fitted
a socket head screw to the thumb screw. This can be accessed
using an allen key via a hole in the bottom of the cover.