■ FIGURE 6.
■ FIGURE 5.
433) and Digi-Key, just add –ND to
the part number (see Figure 4A).
ALTelectronics also has a receiver
(part number RLP434A), but it has a
different pinout; refer to Figure 4B.
It operates at the license free
433.92 MHz frequency — same as
the transmitter. The receiver will
operate on five volts; the transmitter
will operate on a three volt coin cell
(Mouser part number 658-CR2032;
$0.45). The output sets the flip-flop
which stays set until you reset it. The
flip-flop energizes Q1, which turns on
a 90 dB pulsing alarm. This will no
doubt annoy the cat enough that it
will stay away from the door.
You will want to trim the antenna
such that it only alarms when the cat
is within four feet of the
‘parts-placement diagram’ shown in
Figure 5 I remember that it was
powered from a nine volt battery, but
don’t remember the electrolytic
capacitor’s values or how the rest of
the parts were connected.
I don’t remember what I did with
the finished kit, but I’d like to rebuild
it — especially with the mini-audio
transformers and multitude of
germanium transistors I found in a
pair of GE walkie-talkies bought very
cheaply at a Goodwill store.
— Don Franklin
AIn Figure 6, I show several ways to hook up an intercom. Figure 6A uses the DPDT switch and
requires four wires between units.
Figure 6B uses a 4PDT switch and
requires only two wires between
units. Figure 6C is an option that
only needs one amplifier, although
the main unit is always in receive
mode so the remote can initiate a
conversation by speaking into the
mic/speaker. In Figures 6A and 6B,
both units are in receive mode, so
the system is quiet until one pushes
the talk button. In Figure 6C,
however, the main unit is always
listening to the remote — however
irritating that might be. In any case,
the amplifier is shown in Figure 7.
■ FIGURE 7.
K123 L1 L2 L3 . 9
.ac oct 100 1 1E4 ;tran 0 15mS 1mS 10uS
QI read the request from a reader for an intercom
diagram (June 2013;
page 26) and I basically
have the same request.
Can you please re-create
a schematic from the
August 2013 25