www.nutsvolts.com/index.php?/magazine/article/june2013_QA
■ FIGURE 3.
ALook at the circuit in Figure 3. You will have to select a relay coil voltage that is compatible with the motor
voltage; I don’t know what that is.
The relay is magnetically latched with
set and reset coils. The timer —
clocked by 60 Hz and operating from
the 24 volt DC control voltage — will
release the latch in 15 minutes.
Since I don’t know whether the
motor is operated on 24 VDC or 115
VAC, the solid-state relays, RLY1 and
RLY2, are configured to operate on
either. The one shot, IC4, produces a
pulse just long enough to reset the
latching relay.
INTERCOM SYSTEM
QWhen I was a kid, my parents had a Fanon intercom set. My mom used it to wake up my
brother and me every morning so we
could get to school on time. It was a
wired system which had the master
station in the kitchen and two slave
stations (one in my room, the other
26 June 2013
in my brother’s room). I believe it
was wired with a two conductor
cable. These slave stations were
simply cabinets with speakers.
When my mom wanted to talk to
us, she pushed the “talk button.”
When she released the button, she
could hear what my brother and I
said. In fact, she could eavesdrop on
us at any time without us knowing
(like a modern baby monitor). My
brother and I could not hear each
other’s comments. In those days, the
system used a tube amp. I would love
to have a similar system in my house,
but all I see are wireless systems,
cheap battery operated systems, or
very expensive fancy systems.
How hard would it be to build a
modern solid-state equivalent of the
old fashioned Fanon system that I
grew up with? Such a system would
more than meet my needs.
— Guy Fischetti
AIf you look at Figure 4, you’ll see I have replicated the Fanon intercom. When the press-to-talk switch
(SW2) is pressed, the master speaker
is connected to the amplifier input as
a microphone and the amp output is
connected to the two remote
speakers.
