18
Many older telescopes, likes the Compustar, require electrical isolation between the electronics
of the autoguiding computer and those of the telescope computer. Failure to do this can cause
fatal damage to the telescope electronics. Being the Compustar computer module is not
replaceable, we cannot afford to let this occur. The required electrical isolation will be provided
in the form of electrical relay switches.
So, completing the connection between the autoguiding computer and the Compustar computer
module isn‟t as simple as knowing which wires of the RJ-11cable are connected to which pins of
the DB-9 connector. We have to insert relay switches between these two connections. To
understand this fully, we will need to cover a few more topics, including relay switches, the
wiring of RJ-11 cables, and autoguiding “languages”.
Relays
The relays are one of the most important components required for autoguiding the Compustar.
They take the electronic correction signal output from the autoguiding computer and use them to
open and close electrical switches that activate the drive motors in the mount to actually carry
out the corrections. In other words, they take the place of your fingers pushing and activating the
motion control buttons on the upper right corner of the computer module. Also, as mentioned
above, they isolate the electronics of the autoguiding computer from the electronics of the
Compustar computer module so that the former does not damage the latter.
For the longest time, the issue of relays for the autoguider confused the author. It wasn‟t clear
from the Compustar Instruction Manual, or any other literature source on the topic of
autoguiding, whether relays were already provided as part of the electronics inside the Computer
module. If they were, then it really might be a fairly simple matter of wiring the connections
between the RJ-11 cable and the pins of a DB-9 plug. Make no mistake about it; there are no
relay switches inside the Compustar computer module. They must be provided by the Compustar
owner and they must be positioned in the link between the RJ-11 connection coming out of the
autoguiding computer and the DB-9 plug entering the Compustar computer module. In other
words, they are an integral part of component number 5 in the list of components that make up
an autoguiding system shown above. Later, we will assemble a relay box to insert between the
autoguiding computer and the Compustar computer module. It will relay the signals from the RJ-
11 cable to the DB-9 connector.
RJ-11 Cables
As mentioned above, RJ-11 cables look like ordinary telephone cables with modular jacks on
either end, but they are not. It is critical that the reader not try to substitute a telephone cable for
an RJ-11 cable. Telephone cables usually have only 4 colored wires that connect to 4 copper pins
on their male modular jacks. RJ-11 cables have 6 colored wires connected to 6 copper pins in
their modular jacks. However, even if one procures an RJ-11 cable, not all RJ-11 cables are
wired suitably for autoguiding the Compustar. The key issue is the relative orientation of the
(66 strony)
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(68 strony)
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