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C3 is too small. With 0.1uF and and 10k for R11 you have 159Hz -3dB high pass. Try increasing that to at least 1uF. The same goes for R10 - it needs to be a bit larger.
I am not sure what you mean by a filter from 0Hz to 130Hz. Do you want to filter out that frequency range? I thought you were already doing that?
actually the signal I want to detect is between 0 to 130 HZ.... So I needed filter out everything above 130HZ...... But it seems the microphone is not sensitive enough to detect below a 100 HZ.... Are there any other microphones which can detect very low frequency sounds............................... Something from 1 HZ or 5 Hz......
Hi,
some interesting document-development...
World's smallest MEMS microphones with a digital interface:
"TDK-EPC presents what it claims to be the smallest commercially available MEMS microphone worldwide with an integrated digital interface. The EPCOS T4030 measures only 3.25x2.25x1.1mm, make the microphone about 60 percent smaller than alternative products. This allows significantly more compact designs of mobile phones and consumer electronics applications such as MP3 players and digital"
K.
I have been searching something about pre-polarized free field microphones... they seem to be able to detect really low frequencies... What I dont get is what kind of power supply they require... meaning what is the voltage range they operate in... Can anyone tell me if this good for a low voltage and low frequency application............??????????
The problem with the Knowles microphones is they don't draw the frequency response below 100Hz, although some of them are flat to 100Hz. I have used the FG series and some of those are flat to 100Hz as well. It may be worthwhile contacting Knowles and asking them what happens below 100Hz.
The problem with the very tiny microphones is that they are intended for consumer applications so they don't care too much about the LF response.
Bruel & Kjaer probably will do something suitable, but they are usually very expensive.
The circuit I have built with the filter and amplification stage is only for one microphone.... I have built another one for another microphone with the same specification of filtering and amplifying..... Now what I want to do is use a differential amplifier and compare both the signals from both the mic signals so that I have a differential measuring system........................... can anyone suggest me what model of differential amplifier is good for low noise applications................. is it possible to use the same amplifier lmv721 for the differential measurement of both the signals.....
Added after 3 minutes:
here is a diagram to better explain what I want to do... it seems if I use the same opamp... I get 0 or 3V output from my opamp.. which is not exactly what I want to do......
I think he is trying to learn. That is why he is posting here. My biggest frustration is that he keeps changing circuits that do work back to ones that don't. e.g. the input amplifiers were correct earlier on.
The value of the capacitor and the value of the resistor in series with it determines the low frequency response. A 4.7uf capacitor will allow the low frequencies to be 10 times lower in frequency than with a 0.47uF capacitor, if the mic goes that low.
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_ low frequencies needs some (more) mass/volumen of course...