■ FIGURE 2.
Stereo 3. 5 mm mini-phone jack
1/4 inch, mono N.C. phone jack
1/4 inch, stereo N.C. phone jack
you’re after. Finally, the wipers of S2c and S2d lead to
mini-phone plug P2 which is permanently connected to
the microphone input of the computer’s sound card.
We’ll get back to the other two sections of S2 in a
moment, but let’s see how the loudspeakers are handled
next. Jack J6 (a stereo mini-phone affair) is where these
connect. If you trace the wiring, you’ll see that these (left
and right channels) work their way to the bottom lugs of
S1a and S1b. Obviously, S1 is a DP3T switch and is the
unit called output referred to previously. To make
inventory control manageable, you can simply use a
duplicate of S2 by just ignoring two of the sections.
Okay, supposing the wiper of S1 is in the lower
position, then the speaker lines are routed directly to
mini-phone plug P1 which is permanently attached to the
speaker output of the computer’s sound card. We
therefore have normal loudspeaker operation accounted
for. Remember, though, there are a couple of options for
headphones, as well. Let’s tackle them next.
Most fancier over-the-ears headphones terminate
through a larger 1/4 inch stereo phone plug, while smaller
foam types or ear buds sport a 3. 5 mm connector. The
sound card switcher can handle both. J14 is the larger of
the two, while J7 is the mini unit. Both are stereo,
obviously, but notice that J14 is a normally-closed
switching jack. Thus, anytime you plug in the big set it will
override the smaller phones automatically. Again, this cuts
down on the number of switches needed. Obviously,
you’ll only want one set of headphones operable at any
So, J14 or J7 wind their ways to S2a and S2b. You’ll
note that in either the middle or bottom position of these
switch sections, the headphones are permitted to pass on
to S1. The middle position of S1, in turn, shoots the signal
to plug P1 as we saw earlier. In a nutshell, S1 chooses
between the loudspeakers or the headphones.
Sometimes a person likes to use a headset
(microphone and earpiece all in one). We’ve already seen
how the microphone connection of this was handled via
J8, S2c, and S2d. Now, notice that mini-phone jack J5
accepts the earpiece connection in the headset. This goes
directly to switch sections S2a and S2b, and the signals
can be routed to plug P1 in much the same way as the
external headphones were through S1.
Finally, there will be occasions when you don’t want
the sound card output to go to the loudspeakers or the
headphones but rather to a tape deck, stereo system,
guitar amplifier, etc. You’ll observe that this is possible
through the top position of switch S1. In particular, the
output from the computer feeds plug P1 which then goes
to the wipers of S1a and S1b. These, then, are passed to
1/4 inch phone jacks J10 and J11.
You could patch these to a guitar amplifier, for
instance, since that’s the normal size connector employed.
Or, if you want to send the output to a cassette deck, say,
then use RCA jacks J1 and J2. Notice that J10 and J11