Best Microphone Circuits for Connecting to RTB2004 Oscilloscope for Frequency Measurement

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How can I measure the frequency of an embedded device's audible alert sounds with an oscilloscope, and what microphone circuit should I use?

For these 261–987 Hz alert tones, a simple microphone plus amplifier board is enough; one suggested ready-made option is the Adafruit mic/amp board [#21685038] Use the microphone at the right distance to avoid distortion, and if the signal is too low, boost it with a low-noise op-amp such as TL081 [#21685033] A cone of absorbent material, such as cork, can help direct the sound toward the microphone [#21685033] Then feed the amplified microphone output into the oscilloscope and measure one full wave period to calculate the frequency using F = 1/T [#21685033]

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Need a microphone circuit for oscilloscope frequency checks
#1 21685030 23 Sep 2020 09:38

Saneesin Saneesin

Anonymous

Need a microphone circuit for oscilloscope frequency checks
Post #1 21685030 23 Sep 2020 09:38

Hi,
I have an embedded device which generates sound in certain system states like three tone or two tones in certain frequencies. I want to verify that the sounds are generated in the right frequencies using an oscilloscope. In order to achieve this, what type of microphone circuits are available in the market so I can buy and use it to connect to the RTB2004 oscilloscope for frequency measurement? Please advice.

Thanks!
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#2 21685031 23 Sep 2020 16:59

Giovanni Di Maria Giovanni Di Maria

Anonymous

Post #2
21685031 23 Sep 2020 16:59

Hi.
Why use microphone?
It could damage the signal, microphones have a bandwidth 0-16 Khz and your signal to test could have a larger one.
Connect directly your device to an oscilloscope and analyze that signal.
Giovanni
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Need an easier way to measure 261–987 Hz tones
#3 21685032 23 Sep 2020 18:54

Saneesin Saneesin

Anonymous

Need an easier way to measure 261–987 Hz tones
Post #3 21685032 23 Sep 2020 18:54

Hi Giovanni,
Thanks so much for your reply! The frequencies of the signal will range from 261 hz to 987 hz. I already tested the signal using the debug board by connecting directly to the Oscilloscope.It worked.

But as per the requirement, I need to test the assembled embedded device as well. It will alert the user with 3 tone or 2 tone frequency in the above range during certain system mode. We need to test the production devices if they are generating alert in the right frequencies. So that's why I wanted to find out what the options are. Please suggest me an easier approach as I am fairly new to this area.

Thanks again!!
Using a microphone and TL081 preamp for frequency measurement
#4 21685033 24 Sep 2020 09:25

Giovanni Di Maria Giovanni Di Maria

Anonymous

Using a microphone and TL081 preamp for frequency measurement
Post #4 21685033 24 Sep 2020 09:25

Hello Saneesin.
Ok, I understand your need.
If you are only interested in measuring and verifying the frequency, you can use a good microphone at the right distance, without getting into distortion. If the signal coming from the microphone is too low, you can amplify it with a low noise opamp, such as TL081. These frequencies are not critical.
You can also use a frequency meter for confirmation.
To correctly direct the sound towards the microphone you can use a cone of absorbent material (cork).
You can easily calculate the frequency on the oscilloscope by measuring the time duration of a full wave (for example 1200 microseconds) and calculating the reciprocal:
F = 1 / T
= 833 Hz.

Regards
Giovanni
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#5 21685034 24 Sep 2020 09:26

Richard Gabric Richard Gabric

Anonymous

Post #5
21685034 24 Sep 2020 09:26

There are audiuo spectrum analyser apps for smart phones that may be worth a try,
cheers,
Richard
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#6 21685035 25 Sep 2020 08:57

jessewalter375 jessewalter375

Anonymous

Post #6
21685035 25 Sep 2020 08:57

A microphone can be used with an oscilloscope to see the waveforms of various sounds. The oscilloscope may be used to view the shape of the waveform, the spectrum or the frequency response of a loudspeaker or microphone. The speaker and microphone can be used to explore acoustic resonance in an air column1.
Microphone type and test setup questions
#7 21685036 25 Sep 2020 08:59

Saneesin Saneesin

Anonymous

Microphone type and test setup questions
Post #7 21685036 25 Sep 2020 08:59

Thanks Giovanni for the detailed response!

-Can you please give me some pointers on what type of Microphone should I buy? When I google, there are many options like dynamic microphone, condenser, Electret Microphone, etc. I am not sure what option to choose. Please let me know.
-With the microphone & low noise opamp you suggested, how should I set the test up? Should I build a circuit and if so, how and what are the components needed? Is there a website that I can refer which has such information?

Sorry to bother you with so many basic questions!

Thanks again,
Saneesin
Request for a simple microphone-to-oscilloscope frequency setup
#8 21685037 25 Sep 2020 08:59

Saneesin Saneesin

Anonymous

Request for a simple microphone-to-oscilloscope frequency setup
Post #8 21685037 25 Sep 2020 08:59

Thanks Richard for your response! I understand the use case is simple enough that there are many supporting apps to do this. But we have a requirement that this test need to be tested only using Oscilloscope.

Being a newbie, I was hoping I can find a microphone in Amazon, connect to Oscilloscope and measure the frequencies of the sound produced by the embedded device. When I googled it, I could not find any such simple solution. I see people build circuits to achieve this with different components. There are so many type of microphones out there. I am confused in deciding what to follow. Also because I don't have the domain knowledge I am finding it harder. Please let me know if you have any simple solution to achieve the test using Oscilloscope. If so, Please provide the details. That will be very helpful.

Thanks,
Saneesin
#9 21685038 25 Sep 2020 17:30

Richard Gabric Richard Gabric

Anonymous

Post #9
21685038 25 Sep 2020 17:30

Try this, https://www.adafruit.com/product/1063#description">adafruit mic/amp board.
Cheers,
Richard
#10 21685039 28 Sep 2020 09:03

Saneesin Saneesin

Anonymous

Post #10
21685039 28 Sep 2020 09:03

Thanks Richard for taking time to give me a simple solution!! I will try this one.

Thanks again!
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Topic summary

The discussion addresses the challenge of measuring audio frequencies generated by an embedded device using an RTB2004 oscilloscope. The device produces alert tones between 261 Hz and 987 Hz, and the goal is to verify these frequencies in assembled production units. Direct electrical connection to the oscilloscope is possible during development, but for assembled devices emitting sound, a microphone-based solution is sought. It is noted that microphones have limited bandwidth (typically up to 16 kHz) and may introduce signal distortion if not used properly. For frequency verification, a good quality microphone placed at an appropriate distance can capture the sound, and the signal can be amplified using a low-noise operational amplifier such as the TL081. Frequency measurement can then be performed by analyzing the waveform period on the oscilloscope. Among microphone types, electret microphones are commonly used for such applications due to their sensitivity and ease of integration. A practical recommendation includes using a microphone amplifier board, such as the Adafruit microphone amplifier (product 1063), which simplifies interfacing the microphone output to the oscilloscope. Alternative approaches like smartphone audio spectrum analyzer apps exist but are not suitable here due to test requirements restricting measurement to oscilloscopes only. Additional setup tips include using acoustic cones made of absorbent materials to direct sound towards the microphone and calculating frequency as the reciprocal of the waveform period measured on the oscilloscope.
AI summary based on the discussion. May contain errors.

Best Microphone Circuits for Connecting to RTB2004 Oscilloscope for Frequency Measurement

How can I measure the frequency of an embedded device's audible alert sounds with an oscilloscope, and what microphone circuit should I use?

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