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If the device being controlled is electrically isolated, than the 5vDC supply can be used, maintaining a 100mA limit
on current drawn.
The Telos Alliance accessory modules use the 5vDC supply to illuminate LED based buttons. So a one-to-one pin
connection is all that is needed between any accessory modules and a GPIO port.
Note that all of the inputs and outputs on a specific GPIO port are "grouped together". The 5 "Outputs" are on 5
separate output pins, however, they share the same "Common Return" connection on Pin #7. Similarly, the 5 "In-
puts" pins would be pulled to ground to activate them, and they share a common pin for a high-side rail, on Pin #10.
If more than one remotely-controlled device is to be connected to a single 15-pin I/O port, you must make sure that
the two units in question have the same ground potential or ground loops will occur. Therefore, it is recommended
that only one remote device be connected to each I/O port connector to assure complete electrical isolation.
Tid bit of worthless knowledge: The D-sub series of connectors was invented by ITT Corporation, in
1952. Cannon's part-numbering system uses D as the prefix for the whole series, followed by one of A, B,
C, D, or E denoting the shell size, followed by the number of pins. Each shell size usually corresponds to a
certain number of pins: A with 15, B with 25, C with 37, D with 50, and E with 9. For example, DB25 denotes
a D-sub with a 25position shell size and a 25-position contact configuration which was common in the onset
of personal computers. When the PC serial port transitioned to the use of a 9-pin connector, they were often
labeled as DB9 instead of DE9 connectors, due to an ignorance of the fact that B represented a shell size. It
is now common to see DE9 connectors sold as DB9 connectors.
Figure 7-5
Figure 7-6
Figure 7-7
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