This is only a preview of the April 1996 issue of Silicon Chip. You can view 26 of the 96 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Articles in this series:
Items relevant to "A High-Power HiFi Amplifier Module":
Items relevant to "Replacement Module For The SL486 & MV601":
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Items relevant to "Build A Knock Indicator For Leaded-Petrol Engines":
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I have a small problem that you
may be able to help me with. I have
a smoke detector which is working
fine but it gives a low beep at regular
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works in its usual loud and raucous
fashion. What’s wrong with it? (D. S.,
Berala, NSW).
• This is a common problem with
smoke detectors but it is entirely normal. As we pointed out in our February
1996 article entitled “Fit A Kill Switch
To Your Smoke Detector”, these units
produce an audible beep to tell you
when the battery is low.
So the answer is simple: replace the
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Notes & Errata
Radio Control 8-Channel Encoder;
March 1996: in the circuit on pages 56
& 57, R19, the 10kΩ resistor at pin 6 of
IC3b, should connect to pin 5 instead.
It comprises a voltage divider with
R13, a 22kΩ resistor.
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along these lines was published in another Australian electronics magazine
many years ago.
In principle, the circuit needs to
measure the frequency of the local oscillator in the radio and then offset the
reading by the intermediate frequency,
to get the actual incoming frequency.
In an AM broadcast radio with digital
readout, the local oscillator usually
covers the range from about 1MHz to
just over 2MHz and the intermediate
frequency is 450kHz (not 455kHz as
in older AM radios).
By contrast, the local oscillator in
an FM radio covers from 93.5MHz
to 113.5MHz while the intermediate
frequency is 5.5MHz. Since the FM
local oscillator is such a high frequency, a prescaler IC is generally used to
divide the frequencies down to a more
manageable frequency in the region of
about 1MHz.
In practice, digital radios solve the
problems of pushbutton tuning, frequency readout and so on by using a
dedicated microprocessor. It is unlikely that we will publish a project along
these lines in SILICON CHIP.
April 1996 93
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