Context: I have taken on a little side hobby project to learn by making a circuit which should be able to only go high when it sense an acoustic signal with a frequency around 40kHz. To do this I will be connecting a microphone to a band pass filter and then hook it into an arduino which I am somehow going to programme to indicate when this happens:

Main Idea

Microphone > Band pass filter > High voltage when 40k+ goes to Arduino to log this information.

For this whole project I will be using a battery so I will have 0 to +5 volts and so I cannot use -5v in any op amps.

For my band pass filter I have 2 options I can go really simple with something like a passive band pass filter:

enter image description here

Or I can go further and make an active bandpass filter: [ Although I do not understand how it works fully, I know that it is a higher order and is more precise and accurate :

enter image description here

The issue with this is the fact that the ADA4062-2 Op amp is extremely small. I would not be able to solder it or use it in a breadboard. Is there a way to find an op amp that could do this to avoid this issue?

For the Microphone/ultrasonic sensor I will be using this:


My questions:

1) Will using the simple passive band pass filter be enough. 2) Is there a way to find DIL integrated circuits to replace small surface mount ones? 3) In regards to the ultrasonic sensor can I just connect this to the band pass filter directly?

I am sorry for my lack of experience. I would appreciate any help.

Higher order circuit designed using: https://www.analog.com/designtools/en/filterwizard/

  • \$\begingroup\$ Have a look at this website, especially the "Infinite Gain Multiple Feedback Active Filter" section where you can see a band-pass filter with a high Q. electronics-tutorials.ws/filter/filter_7.html \$\endgroup\$
    – Oldfart
    Feb 6 '19 at 22:56
  • \$\begingroup\$ There are better ways to design active filters on TI’s webbench site. 1st define BW and gain then bandstop or order =4 so if you want 1% BW or 0.5% or whatever with high gain then it will tell you the GBW needed and tolerance if parts. I would choose multiple feedback type rather than Salens & Keys then connect Vref to V/2 with cap. Thus gives better R values at high Q. \$\endgroup\$ Feb 6 '19 at 23:05
  • \$\begingroup\$ That piezo microphone is a selective bandpass filter all on its own...you can likely benefit from a few high-pass RC filters to filter out audio. A few transistor amplifier stages should suffice to give a decent signal, since the Arduino AtoD is a high-impedance load. Start off simple. \$\endgroup\$
    – glen_geek
    Feb 6 '19 at 23:29
  • \$\begingroup\$ @glen_geek The ultrasonic sensor itself is a band pass filter? how so? \$\endgroup\$
    – John Skolm
    Feb 6 '19 at 23:47
  • \$\begingroup\$ This type sensor is a piezo-ceramic type, similar to a crystal, resonant at 40 kHz. It is quite sensitive at its resonant frequency, less so at other frequencies. \$\endgroup\$
    – glen_geek
    Feb 7 '19 at 0:18

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