How many inputs are there on a wave shield?
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Re: How many inputs are there on a wave shield?

by keeleon on Mon Mar 11, 2013 10:59 am

The microprocessor provides internal reference voltages of either 1.1V or Vcc (5V on a Uno). Providing a reference voltage through AREF is strictly optional.


The tutorial says it won't work if you don't connect the AREF. Is that because the code is expecting a 3.3v reference? I guess I'll understand how all this works a lot more when I actually get the mic and can start trying it out and seeing what it does.

The microphone can run on 2.4V - 5V, and you match AREF to the supply voltage. We recommend using the 3.3V source on the arduino because it is the 'quietest'. That is, for analog measurements, the 5V supply is not quite as stable a reference as the 3.3V.


Because "5v" can jump around a bit based on the power source, where 3.3v is more strictly controlled by the hardware? So that means I can just solder a jumper straight across from 3.3v to AREF? Some of the images I saw in the non-ada tutorial had resistors. Were those to further fine tune the reference or for safety?
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Re: How many inputs are there on a wave shield?

by adafruit_support_bill on Mon Mar 11, 2013 11:17 am

Is that because the code is expecting a 3.3v reference?

Yes. If your code specifies an external reference, you need to supply one to the AREF pin.

Because "5v" can jump around a bit based on the power source, where 3.3v is more strictly controlled by the hardware?

Because the 5v supply powers all the digital circuits. All the rapid switching of logic signals creates instantaneous surges in current demand which show up as noise on the 5v supply.

Some of the images I saw in the non-ada tutorial had resistors. Were those to further fine tune the reference or for safety?

Those are for safety. If the AREF pin is connected to an external source but the AnalogReference is not set to EXTERNAL, you will create a short between the internal and external supplies when you take an analog reading. The downside of the resistor is that it creates a voltage divider that shifts the reference voltage. See the documentation for more detail: http://arduino.cc/en/Reference/AnalogReference
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Re: How many inputs are there on a wave shield?

by keeleon on Mon Mar 11, 2013 1:45 pm

Those are for safety. If the AREF pin is connected to an external source but the AnalogReference is not set to EXTERNAL, you will create a short between the internal and external supplies when you take an analog reading. The downside of the resistor is that it creates a voltage divider that shifts the reference voltage.


So as long as I make super sure to specify an external reference in my code, I do not need a resistor,and I can just solder a jumper directly from 3.3v to AREF? From my understanding it seems that in any project where I need to read the AREF pin, it is best to go with the 3.3 to reduce noise. Is there a practical situation where it would be better to reference 5v?
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Re: How many inputs are there on a wave shield?

by adafruit_support_bill on Mon Mar 11, 2013 2:10 pm

If the signals you are measuring will reach the 5v level, you will need a 5v reference to measure them. But that reference does not necessarily have to be the Arduino internal 5v reference. If you have a stable external 5v reference, you can specify EXTERNAL and connect that to the AREF pin.
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Re: How many inputs are there on a wave shield?

by adafruit_support_rick on Mon Mar 11, 2013 2:12 pm

For the voice-changer, a stable reference may not be all that critical. 5V isn't wildly unstable - it's just that 3.3V is better for high-precision types of things, like temperature measurements.

You can certainly try it with the default 5V reference. In that case, you'll want to run the mic on 5V. In your sketch, find the call to analogReference(EXTERNAL) and change it to analogReference(DEFAULT)

keeleon wrote:So as long as I make super sure to specify an external reference in my code, I do not need a resistor,and I can just solder a jumper directly from 3.3v to AREF?

There is no such thing as "super-sure". In my experience, the only super-sure thing (besides death and taxes) is that you will someday goof. :wink:

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Re: How many inputs are there on a wave shield?

by keeleon on Mon Mar 11, 2013 2:16 pm

You can certainly try it with the default 5V reference. In that case, you'll want to run the mic on 5V. In your sketch, find the call to analogReference(EXTERNAL) and change it to analogReference(DEFAULT)


I think I'll try that. I'm using it to make a robot voice anyway, so a little fluctuation/noise will probably add to the effect. I haven't even opened the code yet, since I'm waiting for the mic (HURRY UP!), so it will prolly make a lot more sense once I start looking at it. I'm just on a deadline to get this costume working, and I'm trying to understand as much as I can so I can just plug in the pieces and make them work when they show up. ;)

Thanks for all the help!
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Re: How many inputs are there on a wave shield?

by pburgess on Mon Mar 11, 2013 9:37 pm

The reason for the 3.3V AREF is that the microphone amp is being powered w/3.3V. It can work at 5V, but the output sounds a little more 'clean' at the lower voltage.
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