Electronic Stethoscope

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Stethoscopes are not only useful for doctors, but home mechanics, exterminators, spying and any number of other uses. Standard stethoscopes provide no amplification which limits their use. This circuit uses op-amps to greatly amplify a standard stethoscope, and includes a low pass filter to remove background noise.

Schematic

Parts

Part	Total Qty.	Description	Substitutions
R1	1	10K 1/4W Resistor
R2	1	2.2K 1/4W Resistor
R4	1	47K 1/4W Resistor
R5, R6, R7	3	33K 1/4W Resistor
R8	1	56K 1/4W Resistor
R10	1	4.7K 1/4W Resistor
R11	1	2.2K to 10K Audio Taper Pot
R12	1	330K 1/4W Resistor
R13, R15, R16	3	1K 1/4W Resistor
R14	1	3.9 Ohm 1/4W Resistor
C1, C8	2	470uF 16V Electrolytic Capacitor
C2	1	4.7uF 16V Electrolytic Capacitor
C3, C4	2	0.047uF 50V Metalized Plastic Film Capacitor
C5	1	0.1uF 50V Ceramic Disc Capacitor
C6, C7	2	1000uF 16V Electrolytic Capacitor
U1	1	TL072 Low Noise Dual Op-Amp
U4	1	741 Op-Amp
U5	1	LM386 Audio Power Amp
MIC	1	Two Wire Electret Microphone
J1	1	1/8" Stereo Headphone Jack
Batt1, Batt2	2	9V Alkaline Battery
LED	1	Red/Green Dual Colour Two Wire LED
SW	1	DPST Switch
MISC	1	Stethoscope head or jar lid, rubber sleeve for microphone, board, wire, battery clips, knob for R11

Notes

MIC is an assembly made out of a stethoscope head and electret mic. Cut the head off the stethoscope and use a small piece of rubber tube to join the nipple on the head to the mic.

Be careful with the volume, as excess noise levels may damage your ears.

R11 is the volume control.

The circuit marked as optional is not required for the main circuit to function. The optional circuit blinks an LED to the heartbeat as it is heard by the microphone. Even if the optional circuit is not included, sound will still be heard via the headphone jack.

Thanks to audioguru for correcting and improving this original schematic. He has essentially redesigned the circuit as a much improved version. Read about it in this forum topic.

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Comments

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Steven Electronic Stethoscope Friday, August 07, 2009 2:58:07 AM

The 2 batteries are in series to provide +9V and -9V ... see the ground line in between. They will not produce +18V !!!

Jiri Polivka Electronic Stethoscope Thursday, August 06, 2009 11:56:54 AM

A nice project! I detected several weak points: 1. The ordinary electret microphone is not sensitive enough to < 100 Hz where important heart sounds can be heard through a normal stethoscope. 2. Using two 9V batteries makes the instrument heavy, and using LM386 is not good due to a high current consumption. A headphone needs only a couple of mW, not 3 Watts LM386 can generate. 3. If "Stereo headphones" are used, only a mono response can be expected. Why not add another channel, microphone to earphone? 4. I would recommend using only one 9V battery and TL082 opamps. Does anyone know where to find a good small microphone with a good <100 Hz response?

GTN Electronic Stethoscope Tuesday, July 28, 2009 4:01:25 AM

sir mic is working but can't picking the heart beats.could you suggest other mic

fajar Electronic Stethoscope Thursday, July 16, 2009 7:13:58 AM

the power is ok. but the pre-amp not work !!!! why????

Sreenivasan Electronic Stethoscope Thursday, July 16, 2009 5:05:37 AM

Hi sir, i tried this project at our lab, but i couldnt get the exact heart beat as such, but instead we got some electronic sound which we think s of as heart sound. Why we couldnt get the exact heart sound as such?we've assembled as such given in the circuit.....eagerly waiting for reply....regards sreeni

bruno Electronic Stethoscope Tuesday, June 23, 2009 9:12:15 AM

you should find the "Two Wire Electret Microphone" at any electronics shop. Maybe called "capsule ECM" too. Or you could try a piezo-ceramic transductor also (found inside piezo buzzer). These 2 components runs for less than a $ !!!

azar Electronic Stethoscope Thursday, March 19, 2009 6:21:23 AM

sir, here we are facing a huge problem to make this Electronic Stethoscope..everything is ok except the electric mic which can collect the heart beat...we cant find such a mic which can collect the heartbeat and convert it to a voltage...please help us.

anonymous Electronic Stethoscope Wednesday, February 25, 2009 5:51:53 AM

hi ive tried making the unit. ive tried running it, it does not run, LED does not light up, no sound. Battery are warm. can you help me .

Stairo Dalyop Electronic Stethoscope Friday, February 20, 2009 7:47:17 AM

sir,i have try my best but there is some worming sound from the out put.how can i eliminate this sound.

sUBISH Electronic Stethoscope Saturday, February 07, 2009 3:55:24 AM

sir, here we are facing a huge problem to make this Electronic Stethoscope..everything is ok except the electric mic which can collect the heart beat...we cant find such a mic which can collect the heartbeat and convert it to a voltage. if you could send me a photo of how you assembled your components especially fixing mic in the Stethoscope

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Steven	Electronic Stethoscope	Friday, August 07, 2009 2:58:07 AM
The 2 batteries are in series to provide +9V and -9V ... see the ground line in between. They will not produce +18V !!!
Jiri Polivka	Electronic Stethoscope	Thursday, August 06, 2009 11:56:54 AM
A nice project! I detected several weak points: 1. The ordinary electret microphone is not sensitive enough to < 100 Hz where important heart sounds can be heard through a normal stethoscope. 2. Using two 9V batteries makes the instrument heavy, and using LM386 is not good due to a high current consumption. A headphone needs only a couple of mW, not 3 Watts LM386 can generate. 3. If "Stereo headphones" are used, only a mono response can be expected. Why not add another channel, microphone to earphone? 4. I would recommend using only one 9V battery and TL082 opamps. Does anyone know where to find a good small microphone with a good <100 Hz response?
GTN	Electronic Stethoscope	Tuesday, July 28, 2009 4:01:25 AM
sir mic is working but can't picking the heart beats.could you suggest other mic
fajar	Electronic Stethoscope	Thursday, July 16, 2009 7:13:58 AM
the power is ok. but the pre-amp not work !!!! why????
Sreenivasan	Electronic Stethoscope	Thursday, July 16, 2009 5:05:37 AM
Hi sir, i tried this project at our lab, but i couldnt get the exact heart beat as such, but instead we got some electronic sound which we think s of as heart sound. Why we couldnt get the exact heart sound as such?we've assembled as such given in the circuit.....eagerly waiting for reply....regards sreeni
bruno	Electronic Stethoscope	Tuesday, June 23, 2009 9:12:15 AM
you should find the "Two Wire Electret Microphone" at any electronics shop. Maybe called "capsule ECM" too. Or you could try a piezo-ceramic transductor also (found inside piezo buzzer). These 2 components runs for less than a $ !!!
azar	Electronic Stethoscope	Thursday, March 19, 2009 6:21:23 AM
sir, here we are facing a huge problem to make this Electronic Stethoscope..everything is ok except the electric mic which can collect the heart beat...we cant find such a mic which can collect the heartbeat and convert it to a voltage...please help us.
anonymous	Electronic Stethoscope	Wednesday, February 25, 2009 5:51:53 AM
hi ive tried making the unit. ive tried running it, it does not run, LED does not light up, no sound. Battery are warm. can you help me .
Stairo Dalyop	Electronic Stethoscope	Friday, February 20, 2009 7:47:17 AM
sir,i have try my best but there is some worming sound from the out put.how can i eliminate this sound.
sUBISH	Electronic Stethoscope	Saturday, February 07, 2009 3:55:24 AM
sir, here we are facing a huge problem to make this Electronic Stethoscope..everything is ok except the electric mic which can collect the heart beat...we cant find such a mic which can collect the heartbeat and convert it to a voltage. if you could send me a photo of how you assembled your components especially fixing mic in the Stethoscope