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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deepak Electronic Stethoscope Sunday, February 03, 2013 9:30:11 AM

efficient circuit. working good in all aspects

jagadish Electronic Stethoscope Thursday, August 30, 2012 10:44:44 AM

sir would u please mention the cost and complete details of this project please..........

abhipsa Electronic Stethoscope Monday, November 14, 2011 8:50:17 AM

We made the stethoscope but instead of LM386 we used LM380 and instead of TL072 we used LM381 as in another book it was written so.. but in our output while using loudspeakers the volume is too low.. we didnt do the volume control part.. we attached an led in parallel wid speaker to check if the circuit is working, the led keeps on blinking but loudspeaker output is too low. also instead of a mic we used a crystal pick-up cartridge. do we need to shield cable the 3 wires from the pick-up cartridge? please respond asap! thanks!

mostafa zied Electronic Stethoscope Sunday, May 22, 2011 12:51:19 PM

i made this project and it all is working very good .But replace this mic with mobile phone mic this is very small in size and lower in noise....................thanx

chethan Electronic Stethoscope Monday, April 19, 2010 9:54:55 AM

i have done the project.its picking up sound.leds does't match with the heartbeat sound theres lot of buzz sound .and even i have altered it and added a counter to it.it working but the beats are not matching. suggest me something please

pranav Electronic Stethoscope Monday, March 01, 2010 8:21:51 AM

i have made the ckt but its not working and i have no idea about the battery which i have made is correct or not

Harshil Electronic Stethoscope Tuesday, November 24, 2009 12:02:10 PM

its gr8 n ckt is proper, it in workng............thnks

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

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deepak	Electronic Stethoscope	Sunday, February 03, 2013 9:30:11 AM
efficient circuit. working good in all aspects
jagadish	Electronic Stethoscope	Thursday, August 30, 2012 10:44:44 AM
sir would u please mention the cost and complete details of this project please..........
abhipsa	Electronic Stethoscope	Monday, November 14, 2011 8:50:17 AM
We made the stethoscope but instead of LM386 we used LM380 and instead of TL072 we used LM381 as in another book it was written so.. but in our output while using loudspeakers the volume is too low.. we didnt do the volume control part.. we attached an led in parallel wid speaker to check if the circuit is working, the led keeps on blinking but loudspeaker output is too low. also instead of a mic we used a crystal pick-up cartridge. do we need to shield cable the 3 wires from the pick-up cartridge? please respond asap! thanks!
mostafa zied	Electronic Stethoscope	Sunday, May 22, 2011 12:51:19 PM
i made this project and it all is working very good .But replace this mic with mobile phone mic this is very small in size and lower in noise....................thanx
chethan	Electronic Stethoscope	Monday, April 19, 2010 9:54:55 AM
i have done the project.its picking up sound.leds does't match with the heartbeat sound theres lot of buzz sound .and even i have altered it and added a counter to it.it working but the beats are not matching. suggest me something please
pranav	Electronic Stethoscope	Monday, March 01, 2010 8:21:51 AM
i have made the ckt but its not working and i have no idea about the battery which i have made is correct or not
Harshil	Electronic Stethoscope	Tuesday, November 24, 2009 12:02:10 PM
its gr8 n ckt is proper, it in workng............thnks
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