Wouldn't an electret capsule be better? Piezos are limited in frequency response and have an awkward high impedance output. An electret and a preamp based on something like the NE5532 should be good (the Pasnasonic WM-61A capsules are best)
The project literature that I have advices against microphones. It claims that microphones have excessive stray noise capture and cannot have a "solid contact" with the skin.
The litrature suggest usage of a Crystal pickup Cartridge. I have no idea where to procure one from and also the economy is an issue.
Two years ago, I connected the two ends of a piezo buzzer to a CRO and found a 20mV swing. This was a telephone buzzer with a black box and an inbuilt circuit. I now intend to use a brass coin type buzzer and amplifiers instead of the cartrige.
I am aware of the high impedance output of the piezo buzzer. Would it effect if I use an amplifier? After all the amplifier needs only the voltage at the input.
To akg: Are TL071 available easily in India? Is it commonly used in consumer electronics? (An indication of availability in the market)
Oh!.... Is that easily available? Many of these rarely used sensors are not as common as resistors... If I do not find these sensors, I might have to end up changing the project.
I do not mind if there is a noise or so...
Actually, this is a project I was forced to take by forcing me to abandon my earlier project by the teacher.
I see the point about the crystal, I just wouldn't think it would give great low frequencies like a heartbeat produces? The 071 is a good choice as it has FET buffered inputs to give a high input impedance, required for use with the piezo.
The LM380 is still in full production at National Semi. Digikey has thousands in the 14 pins package in stock and Newarkinone has 680 in the 8 pins package in stock.
It is a power amp, not a preamp.
Any circuit that uses an old, old, old, old crystal microphone must be very old.
I see the point about the crystal, I just wouldn't think it would give great low frequencies like a heartbeat produces? The 071 is a good choice as it has FET buffered inputs to give a high input impedance, required for use with the piezo.
My Electronic Stethoscope-2 project uses an electret microphone, a low noise TL072 opamp and a lowpass filter and picks-up low frequency hearbeats fine. I heard my heatbeat clearly. Without the lowpass filter I also heard the TV sound in another room and my dog barking outside. https://www.electronics-lab.com/projects/science/019/index.html