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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Sai Electronic Stethoscope Tuesday, January 12, 2021 4:49:13 AM

The Circuit is super sensitive. But i could able to detect the heartbeat at the first stage of amplifier circuit. (i.e near R11). but when i connect the TRS jack to C6/R5 , i could not able to detect the heartbeat and it is completely no sound in the earphones even i have tried tuning the R11 pot. Could you please let me know why the second stage amplification is failed. Even in first stage amplification output near R11, i could see the pot is tuned to 2.2k (measured using multimeter between Pot Output pin and ground pin) where i can hear humming effect mixed with the hearbeat signal. Pl. provide your suggestion on this.

Sanish Electronic Stethoscope Saturday, May 02, 2015 5:57:30 AM

Are C6 and C8 wrongly marked? Should their locations be swapped?

Amitha Electronic Stethoscope Thursday, March 19, 2015 8:47:32 AM

I made this project, it is working very good . thank you.

cheeko Electronic Stethoscope Monday, October 20, 2014 3:58:59 AM

The pin configuration of U1a ,U1b (as shown in circuit diagram) is not right . CAn you please send the right one

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

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Sai	Electronic Stethoscope	Tuesday, January 12, 2021 4:49:13 AM
The Circuit is super sensitive. But i could able to detect the heartbeat at the first stage of amplifier circuit. (i.e near R11). but when i connect the TRS jack to C6/R5 , i could not able to detect the heartbeat and it is completely no sound in the earphones even i have tried tuning the R11 pot. Could you please let me know why the second stage amplification is failed. Even in first stage amplification output near R11, i could see the pot is tuned to 2.2k (measured using multimeter between Pot Output pin and ground pin) where i can hear humming effect mixed with the hearbeat signal. Pl. provide your suggestion on this.
Sanish	Electronic Stethoscope	Saturday, May 02, 2015 5:57:30 AM
Are C6 and C8 wrongly marked? Should their locations be swapped?
Amitha	Electronic Stethoscope	Thursday, March 19, 2015 8:47:32 AM
I made this project, it is working very good . thank you.
cheeko	Electronic Stethoscope	Monday, October 20, 2014 3:58:59 AM
The pin configuration of U1a ,U1b (as shown in circuit diagram) is not right . CAn you please send the right one
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