QUESTIONS and ANSWERS
they were in the vicinity of the machine, of course.
In my case, the washer cycles in 30 minutes versus 60
for the dryer. So, once the first load is put into the dryer, I
don't need to know when the washer cycle is over (most
of the time). As one of my idiosyncrasies, from the den I
can tell when the washer finishes because it makes a
unique "clunk" only at the end of the cycle.
Your mention of a "smart house" reminds me of the
magazine articles that spend many pages touting the
marvels of a smart home, such as when you can have the
coffee maker prepare your morning coffee while you
sleep or turn the oven on to cook a roast for dinner.
However, someone has to put the roast into the oven, or
put coffee and water into the coffee maker.
My philosophy is that people are getting too lazy and
need some kind of daily physical activity (besides a gym
visit) to keep their bodies working as they should. I
remember an EE professor in the early ‘70s talking about
the "recent" developments in computer-aided circuit
design. He said, "This may be an example of a technology
that destroys the fundamentals that created it." Technology
is great, but many things in our lives need a human touch.
Let me know how this idea works.
Telephone Off-Hook Alarm
QSome of us who still have land lines for one reason or another (security system, etc.) sometimes leave a phone off-hook. How about a system to remind you that the off-hook situation
exists? Since no audio is on the line (just off-hook voltage),
the off-hook warning has to trigger on voltage only, no
signal. A pause in conversation has to be considered, and
the warning/alert needs to last until it’s shut off by the
occupant. The off-hook voltage varies between different
carriers; the off-hook voltage for the privately owned
carrier I have is approximately 13.0 volts. AT&T is
approximately 8. 6 volts.
ALand line telephone systems operate with an on- hook voltage of approximately 48 VDC, an off- hook voltage of 3 to 9 VDC with a current draw of 15 to 20 milliamps, and a ringing voltage of
90 VRMS AC at 20 Hz (these values vary somewhat
between phone companies and distance from the central
office). When the phone is off-hook and idle for a length
of time determined by the phone company, the phone
system will send out an obnoxious tone and a message to
alert the user that they have left the phone handset off the
hook, thus rendering the phone useless.
In the North American Numbering Plan, a quad-frequency tone is used consisting of frequencies 1,400 Hz,
2,060 Hz, 2,450 Hz, and 2,600 Hz, with a duty cycle of
50 percent (0.1s on, 0.1s off). If I were to design an off-hook alarm device, I would use the phone company's
alarm (the hard work has already been done, so let's use
their signal) and I would use a high pass filter with a cutoff
frequency of 200 Hz to eliminate the ringer signal, but
pass the off-hook signal from the phone company
(including those that still use the old GTE 480 Hz alarm).
This filter would feed either an audio amp circuit (if you
want an audio alert) or a full bridge rectifier/capacitor
circuit feeding an LED for a visual circuit or a PIC detector
(if you are into programming).
Fortunately, this circuit has already been incorporated
into commercially-available devices such as the Serene
Innovation HD- 60 at $100+. The HD- 60 is pricy but it is
ready to go out of the box, hearing impaired compatible,
and approved for use with telephone systems. Most
telephone providers are extremely adverse to customers
installing unapproved devices on their systems without
proper isolation (a.k.a., unapproved equipment). This
sounds like a draconian measure, but it is designed to
protect the technicians working on the line from
electrocution (the power company has similar restrictions
for customer devices connected to their power grid).
I found several cheaper indictors, but they all
illuminate all of the time the phone is off-hook, so they do
not meet your requirements to activate when the line has
not been used for a period of time.
Let me know if this satisfies your needs.
QI have a small transistor from which I can only receive static. I opened the radio up and noticed there are several square "cans" that have a slotted screw on the top. Will turning one of
these screws allow the radio to receive AM stations again?
— Barbara Weathers
AI remember my first pocket-sized transistor radio from the early ‘60s. I was a teenager, and the tiny black radio only received the AM (Amplitude Modulated) band (for you
youngsters, this is the band you don't use on the AM/FM
radio) and had to be positioned properly to receive a
signal well. This radio was great because it was portable
since it was powered by a single nine volt battery (which I
still call a transistor radio battery). The other radios of the
day were desk or table models which plugged into the
house power receptacle, so the transistor radio was a truly
mobile device. I was reading everything I could about
radio and television electronics at the time, so I naturally
opened up the radio one day and admired all of the neat
tiny electronic components.
Desktop radios were loaded with tubes/sockets, huge
resistors/capacitors, and point-to-point wiring. They were
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