Is It Okay to Feed 5 Volts Into a Microphone Output Input

NealR

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Using a Microphone to Sense Sound

All,

I am trying to create a simple sound-actuated device.  I thought that I might use the output from a condenser microphone as the input to the ADC on a PIC24F.

So I purchased a microphone from Digikey (Digikey P/N 102-1721-ND, CUI P/N CMA-4544PF-W).  See the following link to the datasheet:

[link=http://products.cui.com/CUI_CMA-4544PF-W_Datasheet.pdf?fileID=1367]http://products.cui.com/C...asheet.pdf?fileID=1367[/link]

I connected the microphone per the measurement circuit on Page 2 of the datasheet.  I was able to see noise-actuated disturbances in the output using my oscilliscope and was quite excited (no pun intended).  But the voltage output was extremely small.  So I connected the output to an LM321 op amp per the circuit shown in the attached JPEG.  I amplified the circuit by GAIN = (1+R2/R1) to about 100X using a couple of potentiometers.  So I essentially amplified the mic output from 5mV to about 500mV+.

The duration of the response is about 25-50 msec.  Is this long enough for the ADC to "see" the disturbance?

Any suggestions?

TIA,
--Neal

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Sincerely,
Neal Rosenblum (KB8PFV)
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MBedder

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Re:Using a Microphone to Sense Sound 2011/12/16 07:00:31 (permalink)

WaltR

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Re:Using a Microphone to Sense Sound 2011/12/16 07:11:31 (permalink)

The duration of the response is about 25-50 msec.  Is this long enough for the ADC to "see" the disturbance?

Depends on the detection method you use. Check the Data sheet (doing the calculations for the ADC) to find out how often you need to read the ADC to detect the pulse.

Another method would be to amplify the mic signal to greater than Vdd and then clamp to Vdd level (digital logic level) and feed a digital input on the PIC that is setup to create an interrupt. This would then be edge triggered and would detect a very short pulse.

NealR

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Re:Using a Microphone to Sense Sound 2011/12/16 07:50:07 (permalink)

Dear MBedder,

Thank you for the quick response.  The ADMP441 looks like a pretty good solution.  It is a module and frees me from having to create a circuit, but the availablity is a bit thin.

I will search for one of these.  I have already checked Digikey, Mouser, etc.

Thanks,
--Neal

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Neal Rosenblum (KB8PFV)
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NealR

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Re:Using a Microphone to Sense Sound 2011/12/16 08:09:35 (permalink)

Dear WaltR,

Thank you for the quick response.

I think that what you are essentially saying is to amplify the mic output by let's say 300X (instead of 100X amplification  that I am currently using).  Then clamp the voltage at about 5 volts.  So rather than seeing something that looks like a spike with a transient response (looks almost like a heart rate monitor), I would see what looks more like square waves.  The square waves would look like TTL high.  I would use a pull-down resistor to hold the signal low when no sound is present.

Thanks,
--Neal

Sincerely,
Neal Rosenblum (KB8PFV)
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MBedder

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Re:Using a Microphone to Sense Sound 2011/12/16 08:25:21 (permalink)

isa.guru

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Re:Using a Microphone to Sense Sound 2011/12/16 08:30:14 (permalink)

Connecting an analog voltage to a digital input is never a very bright idea. You can do a lot better by just making a schmidt trigger then connecting to a digital inpuy, or using a comparator (int or ext)

7th dan instrumentation and controls

leon_heller

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Re:Using a Microphone to Sense Sound 2011/12/16 08:34:47 (permalink)

I'm using a BJT amplifier with an electret mic, feeding a dsPIC ADC input, for speech detection.

NealR

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Re:Using a Microphone to Sense Sound 2011/12/16 10:53:44 (permalink)

Dear MBedder,

I just placed an order for a free sample.  Thank you for the suggestion.

One more question.  With the I2S interface, can I use the SPI on the PIC24F?  I looked at the datasheet, and the ADMP441 output looks similar to the I2C protocol (i.e. clock and data lines) and even more similar to the SPI interface.

I looked at Microchip's website and found the following matrix:  http://www.microchip.com/ParamChartSearch/chart.aspx?branchID=8181&mid=14&lang=en

I searched for PIC24F32KA301 and noticed that there is not a "NO" in the Codec I2S column, but I see no specific reference to I2S in the PIC24F32KA301 datasheet.

Thanks,
--Neal

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Neal Rosenblum (KB8PFV)
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MBedder

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Re:Using a Microphone to Sense Sound 2011/12/16 11:39:48 (permalink)

I2S essentially is an SPI variant with selectable /SS polarity which allows connecting two slave I2S devices using the same 3 lines. It has nothing to do with I2C at all. You can easily use plain SPI with I2S devices.

DarioG

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Re:Using a Microphone to Sense Sound 2011/12/16 16:03:15 (permalink)

Thank you MBedder, I never considered it!
Sampling now... you never know

NealR

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Re:Using a Microphone to Sense Sound 2011/12/27 11:01:12 (permalink)

Dear WaltR,

Happy Holidays.

Can I clamp the voltage using a voltage regulator (i.e. LM7805)?  Or is there a simple RC circuit that I can use?  What is the best way to clamp the voltage?

TIA.

Sincerely,
Neal Rosenblum (KB8PFV)
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NealR

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Re:Using a Microphone to Sense Sound 2011/12/27 11:05:08 (permalink)

Dear MBedder,

Happy Holidays.

I just received my free sample of ADMP441ACEZ-RL7 from Analog Devices.  Now I have to figure out how to deal with the I2S.

Thank you.

Sincerely,
Neal Rosenblum (KB8PFV)
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Maicol

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Re:Using a Microphone to Sense Sound 2012/07/25 15:31:12 (permalink)

Hi All,
I know this is not the AD forum, but, has anyone managed to get ADMP441 to work? I can't find any useful information about it.

Thanks
Maicol

JorgeF

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Re:Using a Microphone to Sense Sound 2012/07/25 18:05:38 (permalink)

Hi

geometrix

Dear WaltR,

Happy Holidays.

Can I clamp the voltage using a voltage regulator (i.e. LM7805)?  Or is there a simple RC circuit that I can use?  What is the best way to clamp the voltage?

TIA.

Clamping such kind of signal can be done with a zenner if the op-amp power is assimetrical (+V , GND), or by two zenners for an op-amp with simetrical (+V , -V) power.
But you probably won't need it. If you powered the op-amp from the same power lines of the PIC, then the amplified signal will be naturally clamped by saturation of the of the op-amp output.

Best regards
Jorge

brownlany1993.blogspot.com

Source: https://www.microchip.com/forums/m621066.aspx

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