
(umm…open). It’s hard to tell which position is which. Some manufacturers of switches
may mark it on their terminals, others may not. You decide which is right, and which in
an illusion, to quote the Moody Blues.
How do you do this? It takes an ohmmeter or a continuity tester, or, better yet, a DMM
with a continuity tester built in. The kind of continuity tester that beeps when you have a
short (closed) circuit is by far the best, because your ears will let you know immediately
which position the switch is in, instead of having to peer at a meter while holding test
leads to the two terminals.
Connect one test lead of the ohmmeter/continuity tester/DMM to one terminal of the
switch, and connect the other lead to the other terminal of the switch. Flip the switch into
one position – if the DMM/Ohmmeter reads zero Ohms or close to zero Ohms, or your
continuity tester puts out a long tone, that’s the closed position. If your DMM/Ohmmeter
reads infinite resistance or your continuity tester stays silent, that’s the open position of
the switch. Flip the switch to the opposite position. You should now get the opposite
reaction from your instrument – if the switch was previously closed, it better now read
open and vice versa. If there is no change, you either have the wrong type of switch or
it’s a bad switch and a bad idea to use it. If there are more than two positions to the
switch, it’s the wrong switch.
So, what better tool is there than a table to tell you what position your switch must be in
to do its thing? Why, nothing, that’s what. Here’s your table:
Closed (shorted) Position
Open Position
Pattern Switches 1 through 16 Bit is low
Bit is high
Merge Switches 1 through 3
Merge On
Merge Off
Random/Pattern Switch
Pattern Mode
Random Mode
8X2/16X1 Switch
8X2 Mode
16X1 Mode
Clock Enable Switch
Clock Input Enabled Clock
Input
Disabled
External Load Enable
(optional)
External Load Input
Enabled
External Load Input
Disabled
Bus 1 Load Switch
Bus 1 Load On
Bus 1 Load Off
Table 3-1: SPST ON-OFF Switch Positions
The
Manual Load
Switch and the
Manual Step
switch don’t care which terminal is
connected to what, as long as the two connections are the right connections. As
mentioned before, the
Invert B
and
Gate Bus
Switch positions are determined by how
you wire them. There’s only one way to mount a rotary pot. Perhaps the only other
components that are orientation sensitive are the LED’s and the rotary Range Switch.
In the case of the Range Switch, you will want to be sure the positions of the switch
correspond to the markings on your panel.
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