Schematics > Audio > Speaker Microphone
Speaker Microphone This circuits
allows you to use a cheap loudspeaker as a microphone. Sound waves reaching
the speaker cone cause fluctuations in the voice coil. The voice coil moving
in the speakers magnetic field will produce a small electrical signal.
The circuit is designed to be used with an operating
voltage between 6 and 12 volts dc. The first transistor operates in common
base mode. This has the advantage of matching the low input impedance of the
speaker to the common base stage, and secondly has a high voltage gain. The
second stage is direct coupled and operates in emitter follower. Voltage
gain is slightly less than unity, but output impedance is low, and will
drive long cables.
Speech quality is not as good compared to an ordinary or
ECM microphone, but quite acceptable results can be obtained. Speaker cones
with diameters of 1 inch to 3 inches may be used. Speaker impedance may be 4
ohm to 64 ohm. The 8.2 ohm resistor value may be changed to match the actual
speakers own impedance.
Title: Speaker Microphone
Source: unknown
Published on: 2005-08-27
Reads: 534
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