Microphone-stethoscope. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Microphone-stethoscope. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Microphones, radio microphones

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1 version

An electronic stethoscope registers vibrations in walls up to 0,5 m thick. If necessary, it can be amplified to the desired value using an additional low-frequency amplifier.

Stethoscope microphone

The vibration sensor is made from a piezoceramic pickup head from a PE-1, TZP-308T player, or ZP-1, TZP-308 piezo emitters are used, which reproduce frequencies well in the range of 800-3000 Hz.

2 version

A frequency response corrector, in other words, a tone control, has been introduced into the circuit. It corrects the rise in the high frequency region of the signal from the sensor. It is quite possible to do without a frequency response corrector, simply by applying a signal from output A1 to resistor R0. The disadvantage of the circuit is the presence of bipolar power. Those who wish can take the scheme of Fig. 2 as a basis and, accordingly, modify it by making it two-stage. The first stage provides pre-amplification with common-mode rejection (especially AC hum). A1 needs to be low noise. The sensor is connected to the ULF by a twisted pair in the screen.

(click to enlarge)

Parts list: R1=R2=100k-500k, R3=R4=1M-5M, R0=5k-100k (volume adjustment), R5=100k-1M (should be much larger than R0), R6=10k-20k (sensitivity adjustment ), R7=100k-200k, R8=10 ohm; C2=0.1uF-1.0uF, C3=0.1uF-1.0uF, C4=0.1uF, C5=0.1uF-0.3uF, C6=C7=C8=0.1uF-0.3uF; A1 and A2 - operational amplifiers 140UD12, 140UD20, 140UD8 or any other with internal correction and in standard inclusion; T1, T2 - KT3102, KT3107 or KT315, KT361 or similar, constituting a complementary pair.

Mounting: on one-sided fiberglass. Capacitors C5, C6, C7, C8 are placed as close as possible to the op-amp. The device must be placed in a tin screen.

3 version

Parts list: R1=100k - 1M, R2=10k - 20k (selected when setting sensitivity), R3=1M - 2M, R4=10 ohm; C1=0.1uF - 1.0uF,
C2=0.1mkF - 0.3mkF, C3=0.1mkF-0.3mkF, C4=0.1mkF, A1 - operational amplifier 140UD12, 140UD20, 140UD8 or any others with internal correction; T1, T2 - KT3102, KT3107 or KT315, KT361 or similar, constituting a complementary pair.

(click to enlarge)

Mounting: on one-sided fiberglass. Capacitors C2, C3 are placed as close as possible to the op-amp. The device must be placed in a tin screen.

See other articles Section Microphones, radio microphones.

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