Microphone

Eric R

Does anyone have a schematic for connecting a microphone to a bs2? I am looking for a change in tone / frequency to a input and hope to measure with pulsin. I would assume this to be a simple task but any comments are welcome.

Thanks!

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Jon Williams

That's not a common task, and a web search may turn up more information. Perhaps searching on "audio to ttl" or something similar will turn up a useful circuit.

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Jon Williams
Applications Engineer, Parallax
Dallas Office

Eric R

Thanks Jon, It would appear as S/PDIF is the answer as it should give a one to one signal conversion from analog to digital. As a side note, the microphone does emit a sinewave with increasing amplitude with sound level and decreased duration with frequency according to the scope. Filtering out unwanted signals may prove to be a problem.

The theory behind the question was to produce a microphone based BS2 that would monitor room noise·level in a·industrial engine room. Once a base noise level has been determined it will be considered the normal·baseline. This BS2 would constantly compare the microphone to a time base and look for a situation above and beyond a predetermined frequency span using pulsin. Crossing this span would indicate a change in the room noise showing either a shutdown or other potential mechanical issue such as a bearing failure and use an output as an alarm.·I understand that this may not have the greatest accuracy and we do monitor conditions via PLC controls so this is just a little project to pass the cold winter months and learn a little more about the BS2.

steve_b

You might look at a frequency to voltage IC.
I know there out there...cuz I picked up one.· Haven't used it yet though.

Send the output of this IC to an A/D and you could then filter out the voltages related to the frequencies you don't want.
I've no idea of the dynamic range of these IC's though.

And as far as the Amplitude....put it through a bridge rectifier and associated caps and make it DC....then in to another A/D.
It might be a good idea to amplify the MIC output as I think it's near line level voltages (1V or so).
If you scale your voltage up before you input it in to the A/D....then you'll be far enough away (hopefully) from the noise floor that it should cause too many falses readings (depending on your amplifier design of course!).

A regular OP-Amp setup should amp you enough!· Aim for about 3-5volts (depending on your A/D input limits).

OR....just use an op-amp comparator and connect your mic.· When the mic gets to X level, the comparator triggers and you could then read that as a 1 or 0 input in your Stamp.
Of course your setpoint tuning is now external to the Stamp and requires human adjusting.· Unless you try one of them digital pots!

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Steve
http://members.rogers.com/steve.brady
http://www.geocities.com/paulsopenstage

"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."