HI, i am using the circuit(in picture) for making a piezoelectric contact mic. I got this circuit from link. i am building a digital stethoscope and the frequencies of interest are 5-20 Hz.
My problem is that I now need to digitize this signal to be able to process it. I simulated the circuit in LTSpice, and these are the results:
Can anyone tell me how I can proceed to digitize any signal received from the pre amplifier?
Which amplifier and ADC can i use to convert the signal into digital format? My frequencies of interest are 5-20 Hz
My problem is that I now need to digitize this signal to be able to process it. I simulated the circuit in LTSpice, and these are the results:
Can anyone tell me how I can proceed to digitize any signal received from the pre amplifier?
Which amplifier and ADC can i use to convert the signal into digital format? My frequencies of interest are 5-20 Hz
An inexpensive ADC based on dual-slope or successive approximation would do. Audio grade ADCs are clearly not necessary. I'd look at something 8-12 bits and few ksps, that's it.
Audio grade ADCs can be extremely cheap though - it depends how you want to be able to process the data? If using an audio ADC beware those with built-in high-pass filters as that would take out some of your frequency range...
Not an answer to the question, but I think C3 and C5 are connected incorrectly.
That is, I understood from an earlier thread that the source has a capacitance of 15 nF, so presumably C5 has to be in series with the ideal voltage source so they together model the signal source. C3 then attenuates the signal by a factor of 7.3333...
That is, I understood from an earlier thread that the source has a capacitance of 15 nF, so presumably C5 has to be in series with the ideal voltage source so they together model the signal source. C3 then attenuates the signal by a factor of 7.3333...
~27Hz is a popular low-cut frequency in the audio world, the ones with DC response are the safest ones to pick.
I have not analysed the circuit. what change do you propose? I will simulate in LTSpice and get back to you
Thanks for the reply but the signal has a very low swing, do I need an amplifier before the ADC?
I think C5 should be in series with the signal source, and C3 should be removed.
R1 should then be increased to 4.7 Mohm or so to get a reasonably flat response to 5 Hz. If the bias current of the op-amp then causes too much voltage drop, you either have to correct for it (by reducing R2, for example) or use a FET op-amp.
Yes, a PGA could maximise the bits occupied by the signal. The PGA gain could then be controlled either manually by the user or automatically by the downstream microcontroller / DSP / other DAQ system, depending on the resulting signal strength converted by the ADC. Without an amplifier, you'd be getting very few bits and more of noise.