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Single-Stroke AC Bell
We would like to operate a single-stroke AC bell that would ring once
every time the phone rings in
cadence. The telephone line power —
40 to 120 VAC at 15 to 60 Hz —
should power the bell. We prefer no
external power supply. A typical
single-stroke bell has a coil voltage
of 24 VAC drawing 0.5 amps. Coil
resistance is 10 ohms.
#11111 Michael Lenihan
Better Radio Communications
I’ve been a reader for some years,
and electronics is my daily work. Now,
I have to work with the Motorola PTP
600 radio. The system I am working
now has three sets of PTP 600. They
were set up the same way at three
different locations to communicate to
the main control hub. One of the
stations has kept the connection
pretty well since the first day, but the
other two sometimes show slow or
very slow data transmit. Looking at the
status — as they are all set up with
i_DFS — the link capacity sometimes
drops to 20, the transmit in teens, and
the vector error goes up positive.
Please show me how I can get them to
work more stably. I am working in the
war zone of Afghanistan!
In Cold Weather
I built the "Mail Delivered
Detector" published in the June ‘06
issue of N&V (http://nutsvolts.texteri
was quite satisfied with the results.
However, I found that the device
stopped working in the cold weather.
Adjusting the 25K pot on the
receiver's 567 tone detector restored
operation until the temperature
78 November 2011
changed and the device stopped
As an example, I measured the
frequency of the transmitter's 555
timer at 68 degrees F to be 320 Hz,
and at 20 degrees F it was 280 Hz.
Can someone suggest any modification which will keep the 555 timer
circuit in the transmitter on frequency
as temperature varies between minus
10 degrees and 95 F, or a way to
broaden the frequency range of the
tone detector in the receiver?
#11113 J. G. Jones
Passive Mixer Problems
I've built this passive audio mixer
that I really like. The only problem is
that anything going through it sounds
like it's in a stream of water. Lots of
After the mixer, it goes into the
line level input of an old Teac audio
cassette machine. Anything plugged
into the cassette machine without
going through the little mixer sounds
great. The signal to noise is great. Very
little white noise is present. What type
of pre-amp do I need on each input to
et the signal up high enough to
override the white noise that my
passive mixer generates?
I would like to make a special
power supply/converter with a
difference. It can be supplied from:
• A nominal 12 VDC (nine to
15 actual) from a vehicle supply.
• Or by a nominal 24/28 VDC
supply ( 20 to 32) from a vehicle or
• Or, by international mains (90 to
• All three inputs need to be
isolated and capable of being
accidentally or deliberately connected
at the same time.
• Have all three inputs tolerant to
transients, e.g., mains derived from
The unit needs to have four outputs, all of which are DC and each of
which is configurable internally by a
trim pot to deliver four output voltages
between 10 and 24 VDC (e.g., 12V,
15V, 18V, and 22V).
• Output to be unaffected by
change of input source.
• Once set, each output voltage
needs to maintain a tolerance of ±0.5
VDC, regardless of input changes.
• Each output to be capable of
delivering 120 watts.
• Robust, portable unit.
I understand that these parameters are often mutually exclusive, but
the following considerations are also
• Low weight.
• Small size.
• Low heat dissipation.
• Low noise.
• Low interference.
• High quality.
If the overall concept is too big,
perhaps someone could direct me to
previous power conversion solutions
that may be married together to give a
solution, and highlight the isolation
issues that may apply regarding multiple input connections.
#11115 Kevin Dickinson
Mudgee, NSW Australia
Power Failure Circuit
Our church has analog controlled
dimmer modules. The controller has
four scenes learned in some type of
memory. After a power failure, the
controller does not know the state it
was in at the time of the failure. The
default setting is that the controller
selects scene 4 after the power is
restored. Since most of the time the
power interruptions are at night when
the church is not occupied, the system
is wasting energy. For safety reasons,
this was acceptable at one time, but