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Topic: speaker level input (Read 3472 times) previous topic - next topic

spruce_m00se

hi guys

I need to take off the speaker from a circuit and connect that output to an arduino input pin so that the signal can be processed,

the speaker level is low, ( i havent measured) but its a small 2w speaker, so there wont be a lot of voltage, and i can manually turn down the volume if neccesary,

my question is, I have read that a neg voltage will damage the input pin, and i know speakers work with inverted waves, (neg volts)

is there a way to connect it, block the neg volts and still have a good enough sound to be recognised?

thanks for any help offered

Grumpy_Mike

Yes you need to bias the input at 2.5V with a potential divider, and couple into it from the speaker with a capacitor, like they do here:-
http://interface.khm.de/index.php/labor/experimente/arduino-realtime-audio-processing/

spruce_m00se

so ...... . . . . .  .  .   .    .    .

i guess the part of their schem i need is the part on the attached file,

i guess the pot is for trimming the voltage divider,

do I need the cap marked in the red circle?

and will this circuit sort out the neg voltge problems? will tone length be affected?


Grumpy_Mike

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i guess the part of their schem i need is the part on the attached file,

No it is on the web page, everything to the left of the arduino.

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i guess the pot is for trimming the voltage divider,

Yes the one marked DC offset is.

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do I need the cap marked in the red circle?

I can't see that on the web page. It shows a 10uF cap doing the coupling.

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and will this circuit sort out the neg voltge problems?

Only if your audio signal is less than 5V peak to peak.

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will tone length be affected?

No idea what you mean.

spruce_m00se

oooops.

by attached file i refer to the one i meant to attach but didnt,

by the tone length, I assume (peerhaps erroneosly) that if i effectivly clip the negative parts of a waveform that the length of the ave may be changed?

Grumpy_Mike

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I assume (peerhaps erroneosly) that if i effectivly clip the negative parts of a waveform that the length of the ave may be changed?

No if you clip the negative part of the wave it just sounds distorted.

That cap is to reduce any noise generated by the potential divider. It is too small to have any noticeable effect on the low frequency sound waves.

Magician

What kind of speakers? If it USB powered, may be you can "hack" into, and take DC biased output, than you don't need anything else.
Look here : http://coolarduino.wordpress.com/2012/06/22/audio-input-to-arduino/
Scroll to the middle of  page.

spruce_m00se

just a normal speaker output on a radio ,

Magician

Portable? Can you open it up?

spruce_m00se

yes,

i have it open infact, the plan is to clip the speaker off and connect it to the arduino like mike pointed out, i will try tommorow when i am at work,

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