09-05-2012, 03:52 PM
Electronic Stethoscope
[attachment=21701]
Why a Stethoscope?
Stethoscopes are not only useful for doctors, but for
home mechanics, exterminators, spying etc. Standard
stethoscope provides no amplification which reduces its
use. A Stethoscope uses op-amps to amplify the signal
and includes a low pass filter to remove background
noise.
Circuit Description
A Stethoscope operates as a low-noise microphone
pre-amp. Its gain is only about 3.9 because of the high
output impedance of the drain of the FET inside the
electret microphone causes U1a’s effective input
resistor to be about 12.2K. C2 has a fairly high value in
order to pass very low frequency (about 20 to 30Hz)
heartbeat sounds.
How to assemble?
1) Assemble the circuit using Veroboard (stripboard) or
a PCB.
2) Use a shielded cable for the microphone as shown
on the schematic diagram
3) The microphone/stethoscope’s head must not be
moved while listening to heartbeats to avoid friction
noises.
Features
Operation of an electronic stethoscope is very
simple and intuitive. The following are the features of
an electronic stethoscope.
Hear chest sounds, fetal sounds, and check blood
pressure through clothing layers.
Direct conversion of sound from the chest to
electronic signals minimizes SOUND INTERFERENCE.
Ideal stethoscope for use in air and ambulance
transport of patients.
Separate adjustable filter and volume controls.
[attachment=21701]
Why a Stethoscope?
Stethoscopes are not only useful for doctors, but for
home mechanics, exterminators, spying etc. Standard
stethoscope provides no amplification which reduces its
use. A Stethoscope uses op-amps to amplify the signal
and includes a low pass filter to remove background
noise.
Circuit Description
A Stethoscope operates as a low-noise microphone
pre-amp. Its gain is only about 3.9 because of the high
output impedance of the drain of the FET inside the
electret microphone causes U1a’s effective input
resistor to be about 12.2K. C2 has a fairly high value in
order to pass very low frequency (about 20 to 30Hz)
heartbeat sounds.
How to assemble?
1) Assemble the circuit using Veroboard (stripboard) or
a PCB.
2) Use a shielded cable for the microphone as shown
on the schematic diagram
3) The microphone/stethoscope’s head must not be
moved while listening to heartbeats to avoid friction
noises.
Features
Operation of an electronic stethoscope is very
simple and intuitive. The following are the features of
an electronic stethoscope.
Hear chest sounds, fetal sounds, and check blood
pressure through clothing layers.
Direct conversion of sound from the chest to
electronic signals minimizes SOUND INTERFERENCE.
Ideal stethoscope for use in air and ambulance
transport of patients.
Separate adjustable filter and volume controls.