Description:
A
simple Intercom made with a single transistor and low power audio
amplifier LM386. The circui uses 8 ohm speakers, which also double as a
microphone.
Circuit:
For the first time, this circuit
was is a Canadian/English design and designed by Mr Laurier Gendron of
Burnaby in British Columbia, Canada, and myself. Please make sure you
visit Laurier's web site, Handy Dandy Little Circuits. This page is
also available in French by clicking on the flag.
In this
doorphone circuit, an 8 ohm speaker is used both as a microphone and
also an output device. The BC109C stage amplifies in common base mode,
providing low input impedance to match the speaker and good voltage
gain.
The 270k resistor provides simple DC bias and the load resistor
is 27k. The speaker produces a weak varying DC output when used as a
microphone typically several 100uV. This varying DC signal must be
separated from the fixed DC bias voltages and this is done by the 100u
and 0.47u capacitors.
An LM386 is used in non-inverting mode as a
power amplifier to boost voltage gain and drive the 8 ohm speaker. The
10k potentiometer acts as the volume control, and overall gain may be
adjusted using the 5k preset. The gain of the LM386 can be as high as
200, this is required because of the small audio signal from the
speaker. The double pole double throw switch, reverses the loudspeaker
positions, so that one is used to talk and the other to listen. Manually
operating the switch (from inside the house) allows two way
communication.
Source: www.zen22142.zen.co.uk
Jumat, 10 Oktober 2014
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The article is much informative which i was searching for .Nice intro good explanation thanks for sharing.Enrgtech Electronic Distributor
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