Electronic projects

you are here: home page :: projects :: Audio :: amplifiers :: Speaker Microphone Circuit

Speaker Microphone Circuit

This circuit takes an ordinary loudspeaker and allows it to be used in reverse, as a microphone.

Circuit diagram

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.

author: Andy Collinson
e-mail: anc@mitedu.freeserve.co.uk
web site: http://www.zen22142.zen.co.uk
project categories:
folder Audio (49)
folder Power & high voltage (43)
folder Radio (23)
folder Light & LED (31)
folder Tools & measurement (40)
folder Telephone (18)
folder Automotive (10)
folder Microcontrollers (12)
folder Sensors & control (47)
folder Timers & oscillators (40)
folder Miscellaneous (26)

StumbleUpon button

Share this page
Bookmark and Share
project subcategories:
All subcategories
preamps, filters, effects
VU meters & spectrum analyzers

similar projects:
100W RMS Amplifier
10W Audio Amplifier with Bass-boost
10W Mini Audio Amplifier
18W Audio Amplifier
200W audio amplifier
22 Watt Audio Amplifier
25W Mosfet audio amplifier
2N3055 Power Amplifier
5,000W ultra-light, high-power amplifier, without switching-mode power supply
50 Watt Amplifier

recently added projects:
Doorbell for the Deaf
High Quality Intercom
Combinational Conjuring Trick
Ultrasonic Dog Whistle
Quiz Circuit
LED Torch
Insect Repellant
Speaker Microphone Circuit
Magic Wand Conjuring Trick.

most popular projects:
Led display digital Voltmeter
500W low cost 12V to 220V inverter
Low pass filter - Subwoofer
Metal Detector
Basic UPS Power Supply
2N3055 Power Amplifier
High And Low Voltage Cut Off With Time Delay
200W audio amplifier
LED Torch
100W RMS Amplifier

DIY Electronics Projects

Promote Your Page Too