Electronic Stethoscope

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

1. 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.
2. Be careful with the volume, as excess noise levels may damage your ears.
3. R11 is the volume control.
4. 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.
5. 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.