Arduino Micro emit high frequency noise on battery power

[leadgtr7]

Hello All,
I am new to the world of arduino but I am liking it more day by day. I have been through a couple guitar related projects and have a question. I am trying to wirelessly control my guitar pickups. I have already written the code and everything works great on that end but i have a huge problem. When I power my arduino with a standard 9v battery the arduino makes a terrible whine which is then picked up by the guitar pickups and is amplified (no bueno). When i power the arduino with the usb port all is well and no noise can be heard. Some additional info.... I have tried this on my other micro and have had the same result. I can actually hear the micro screeching away just guessing i would say it is probably in the 8k to 16k range. My question is how do I get rid of this noise. powering the micro from usb is not possible and powering with a 9v is the preferred way as it easy to stash one in the guitar case. Does any one have any insight? I am guessing it has something to do with the on board regulator. Any help would be great

[adafruit_support_mike]

How much current are you trying to draw from the battery, and how do you have the pickups connected to the Micro?

It sounds like the pickups are putting enough of a load on the Micro that the 9v battery can't quite keep up. That would show up as a change in its effective resistance, which could mess up the regulator's ability to keep the voltage stable.

[kengineer]

Hello,

You might be suffering from the same issue I am suffering from at the moment (viewtopic.php?f=25&t=62331)

Have you probed the 5V line while on battery power? Try number 4, 5 and 6 in my first post and tell us the result.

[leadgtr7]

Hi All,
Thanks for the quick replies. Some background on my circuit
The arduino is opto isolated by 2 solid state relays built into a dip package (Panasonic TLP 2 something)
The only thing drawing current from the battery is
-The ssr which draws about 5ma per channel and there are two channel so ~10ma there
-I also have a rf24 module hooked up as well but I'm not sure how much current that draws
the problem I see with the current theory is that it doesn't oscillate when under usb power??

kengineer,
I am right in saying you put a capacitor across your power supply and everything worked well?

thanks for the help!

[kengineer]

kengineer,
I am right in saying you put a capacitor across your power supply and everything worked well?

Not across the supply rather across the Vin / GND pin. Meaning that I put it as close to the Arduino as possible.

It does not oscillate for me either when I power it from the USB port or power it from the 5Vin pin for that matter which leads me to believe that the culprit is either the regulator or the polarity protection FET (or both together?). Unfortunately I am only able to perform non-intrusive tests since I will be returning the Arduinos (My boards are already mounted / manufactured and a respin is not an option).

[adafruit_support_bill]

the problem I see with the current theory is that it doesn't oscillate when under usb power

USB power does not go through the Arduino's regulator. It is regulated at the source USB port.

[leadgtr7]

So when you put the cap across the Vin and Grd on the arduino you don't get the high frequency noise?

[adafruit_support_bill]

I haven't reproduced the exact symptoms you are describing, but if your regulator is oscillating due to insufficient battery power, adding a capacitor across the inputs would most likely lower the frequency of oscillation.

[kengineer]

So when you put the cap across the Vin and Grd on the arduino you don't get the high frequency noise?

That is correct.

What I have not tried yet is placing the cap across the 5V line.

Judging from my report however I would say the noise is in the 3.5khz range for me.

[leadgtr7]

So it looks like soldering a 100uF cap across Vin and Grd has solved the problem (I hope) if not I will post back. Thanks for all the help!