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I need a circuit to detect and filter 10 KHZ sound

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Navid T

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Hi friends
I need a way to detect 10 KHZ sound, I use simple electret microphone with pair of 2N2222 transistors as aplifier, the problem is with other frequency noises on it, i want to filter other sounds below 8 khz and upper than 11 khz, can someone suggest me a filter or circuit?
I use electret microphone because of it's low price, can i use anything instead of microphone?
Regards
 

Navid T said:
Hi friends
I need a way to detect 10 KHZ sound, I use simple electret microphone with pair of 2N2222 transistors as aplifier, the problem is with other frequency noises on it, i want to filter other sounds below 8 khz and upper than 11 khz, can someone suggest me a filter or circuit?
I use electret microphone because of it's low price, can i use anything instead of microphone?
Regards
Click to expand...

Here is a 3rd order butterworth filter for your application. You can modify the parameters using the following online tool.

You should put the correct value for the impedance from your microphone, at the moment for my calculation was 50 ohm.

If you need also amplification of your signal then you should consider design an active filter. Analog devices has a great tool for that too https://www.analog.com/designtools/en/filterwizard/

View attachment rlc_filter.pdf
 
You provided almost no specifications for the circuit you want:
1) Voltage gain at 10kHz?
2) How much reduction at 8kHz and below?
3) How much reduction at 11kHz and above?
4) How much output voltage and current?
5) What power supply or battery voltage?

What product do you have that produces 10kHz?
 

Thanks friends
mic.jpg
As you see i have electret microphone and transistor amplifiers, VCC is 5V and my output is "signal" wire, usually most of frequncies and speaking sounds are on my output, i want to use 10 KHZ, below 8 khz and above 11 khz signals should be as less as possible. finally i wan't to use it as microcontroller digital input.
If i say simple, I need circuit that use audio signal from microphone and give me logic 1 for 10 KHZ and logic 0 for other frequencies below 8000 or 9000 and above 11 khz!!
i need simple and cheap way not complicated filters and chips.
 

If you want 8 kHz and 11 kHz to be read as zero and 10 kHz as one, they you will need a very high order bandpass filter. Alternately, you can use a local osc at 10 kHz, mix that with the output of the microphone and low pass filter the result from the mixer to about 1 kHz. You will catch all input at the microphone at 10 kHz +/- 1 kHz
 
You might check if NE567 tone decoder IC is suitable for your purpose. It should work if your signal is a continuous tone of some duration.

If we consider a bandpass, e.g. 1 kHz bandwidth (9.5 .. 10.5 kHz pass band) and rectifier to determine the sound level, do you intend an absolute threshold (sound level in the given band > xxx dB C) or relative threshold (e.g. in band sound level > 50 % of wide band sound level)?
 
Why do you want to detect only 10kHz and no other frequencies?
What will be producing 10kHz?
What will the microcontroller do when 10khz is detected?

Of course you need a complicated filter circuit with chips.
 

If you can get a ceramic filter for 10 kHz, then you can use that as a bandpass filter with high selectivity but then I am as ignorant as ...
 

What i would do:
-1) add a bandpass filter. Bandpass filters are not the simplest to calculate, but all of the major IC vendors offer free filterCAD software, which will calculate it for you based on requirements.

-2) add a 4046 PLL, with a center frequency of 10 Khz and employing both R1 and R2 to limit the VCO range between 9 and 11 Khz. Use the PCP output to detect when it is locked.
The PCP output can feed then your microcontroller.

This last technique is outlined in an old RCA app note, ICAN-6101. And the example it provides is precisely for 10 Khz.
 
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