Hello everyone. I am currently working on a project and I don’t know where to begin.

The purpose of the project is to compare a relative sound frequency to my sound reference frequency. Once the circuit detects the inputted sound frequency equals to my reference frequency, then the signal will send the signal to a MCU to start the operation. I don’t know how to start especially in frequency comparing. This is urgent.

Basically I have a microphone, a led for indication.

Thank you for your response.

 

hi,
You could start by reading this PDF for a tone decoder.
This type is a bit outdated
E

 

How about an analog narrow bandpass filter (uses opamp, Rs and Cs) , followed by a peak detector (a form of AC to DC rectifier, uses opamp, diode, Rs and Cs). This can be read by the MCUs ADC, comparitor, or even a digital input port pin.

 

Could you just send the sound signal to the MCU and let the MCU analyse it to determine frequency?

 

If you want to do it in hardware external to the controller, you might want to try this circuit:

http://www.talkingelectronics.com/ChipDataEbook-1d/html/567.html

 

How about an analog narrow bandpass filter (uses opamp, Rs and Cs) , followed by a peak detector (a form of AC to DC rectifier, uses opamp, diode, Rs and Cs). This can be read by the MCUs ADC, comparitor, or even a digital input port pin.

Wow thank you, this actually i am looking for. But it confuses me, is the center frequency is the reference frequency i wanted on my design? I am planning to make it 40Hz. Like in the circuit i inserted in here? it shows the 3khz and so on. Thank you.

 

Wow thank you, this actually i am looking for. But it confuses me, is the center frequency is the reference frequency i wanted on my design? I am planning to make it 40Hz. Like in the circuit i inserted in here? it shows the 3khz and so on. Thank you.

The circuit you posted is more complex than you need. First, it has three channels; you need only one. It has a pre-amp IC1a, which you may not need.
It requires a 12V supply; yours is likely 5V. It's lowest frequency channel is centered on 100Hz, you want 40Hz. It drives LEDs; you want a logic level output compatible with a MCU.

What you have not told us is the required sensitivity (smallest signal to be detected), and bandwidth (how close to 40Hz does the signal need to be and still be detected)?

How much work are you willing to do, or do you just want to copy a circuit without understanding it?

 

The circuit you posted is more complex than you need. First, it has three channels; you need only one. It has a pre-amp IC1a, which you may not need.
It requires a 12V supply; yours is likely 5V. It's lowest frequency channel is centered on 100Hz, you want 40Hz. It drives LEDs; you want a logic level output compatible with a MCU.

What you have not told us is the required sensitivity (smallest signal to be detected), and bandwidth (how close to 40Hz does the signal need to be and still be detected)?

How much work are you willing to do, or do you just want to copy a circuit without understanding it?

Yes an Led for indication that the ~40hz(Or closest to 40Hz) has been detected. And yes a logic level that is compatible with mcu.
A bandwidth that is close to 33Hz up to 50Hz might work. And sorry, i am not familiar with this circuit. Can you please explain to me the Sensitivity? What sensitivity you are trying to say? i really don't have idea. Thank you...

 

Yes an Led for indication that the ~40hz(Or closest to 40Hz) has been detected. And yes a logic level that is compatible with mcu.
A bandwidth that is close to 33Hz up to 50Hz might work. And sorry, i am not familiar with this circuit. Can you please explain to me the Sensitivity? What sensitivity you are trying to say? i really don't have idea. Thank you...

In this circuit? Is the center frequency and the reference frequency i am aiming is the same if i follow the mathematical procedure written on the link http://www.ecircuitcenter.com/Circuits/MFB_bandpass/MFB_bandpass.htm ?

 

the required sensitivity (smallest signal to be detected)? How many V or mV?

 

In this circuit? Is the center frequency and the reference frequency i am aiming is the same if i follow the mathematical procedure written on the link http://www.ecircuitcenter.com/Circuits/MFB_bandpass/MFB_bandpass.htm ?

Yes. You will have redesign the circuit to be centered at 40Hz, and then determine if the resulting circuit has a sufficiently narrow bandwidth to meet your specs.

That still leaves the question of the rectifier part of the circuit. Is the simplistic diode in the posted circuit sufficient, or do you need the higher sensitivity offered by the active peak detector I linked to earlier?

 

the required sensitivity (smallest signal to be detected)? How many V or mV?

I get it! it is about mV!

 

Yes. You will have redesign the circuit to be centered at 40Hz, and then determine if the resulting circuit has a sufficiently narrow bandwidth to meet your specs.

That still leaves the question of the rectifier part of the circuit. Is the simplistic diode in the posted circuit sufficient, or do you need the higher sensitivity offered by the active peak detector I linked to earlier?

I think a peak detector will do.
Can you please explain to me it further?


"determine if the resulting circuit has a sufficiently narrow bandwidth to meet your specs."

 

..."determine if the resulting circuit has a sufficiently narrow bandwidth to meet your specs."

You need to understand Q and bandwidth of your filter. Google these terms.

Some reading for you

 

You need to understand Q and bandwidth of your filter. Google these terms.

Some reading for you

Now it seems like things are clearer now. Thank you....

 

Hello! I urgently needed help. I am done with the filter redesign. Then next is the peak detector circuit. I am confuse where to place the peak detector circuit? before or after the filter? Here is my block diagram.

 

Why did you put the peak detector (rectifier) ahead of the filter?

 

Why did you put the peak detector (rectifier) ahead of the filter?

That is why i am asking sir. So it supposed to be after the filter sir?

 

That is why i am asking sir. So it supposed to be after the filter sir?

Do you want to detect the unfiltered signal, which has all frequency components, or the filtered signal, which has only a narrow band of frequency components?

 

Do you want to detect the unfiltered signal, which has all frequency components, or the filtered signal, which has only a narrow band of frequency components?

I think it is Unfiltered sir which has only a narrow band freq components.