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Author Topic: Serial Communication Produces Noise on Breadboard Power Rails  (Read 687 times)
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I've got my arduino hooked up to my computer via Sparkfun's FT232RL breakout board. I'm using the Arduino IDE's serial monitor to collect audio data.

When serial monitor is not open, the voltage between my power and ground rails on my breadboard is very flat, with no fluctuations.

But, when I open serial monitor, I get noise on the power rails on the order of 400 mV peak-peak. This happens to directly feed into my audio signal, which produces a nasty hiss when I listen to it with headphones.

The 'noise' on the scope is actually a series of pulses about 9 uS apart which decay over the course of 1 uS. I assume this is directly related to the serial activity between my arduino and computer. The behavior also persists on my Arduino Uno board (not implemented on a breadboard), so I don't think it's an issue with my own wiring.

I would like this noise to not affect my audio signal. Has anyone else run into this issue and found an acceptable solution? I am alright with circuit design, although certainly not an expert. Any help would be appreciated. Thanks!
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BTW I'm using an ATMega328.
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First thing I would try would be additional bypass capacitance on the power rails, especially right next to your audio circuit.  (If you post the circuit diagram you'll get better help…)

Some USB cables have RF chokes built in.  One of those might help, too.

-br

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thanks for the quick reply, billroy.

I added a couple 470 uF caps along the rails and it definitely lowered the amplitude of the noise. I simply attached headphones to the power rails and was able to hear a qualitative difference immediately upon doing so.

But, there is still noise on the rails, which I am guessing I won't fully be able to rid myself of. Luckily the final PCB design won't need serial communication. It's really just for testing at this stage.

So from here I will most likely take in this noise data and attempt to filter it out when I try for a clean signal.

Further suggestions on getting rid of this serial noise are welcomed and appreciated. Thanks!
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The last thing you did is where you should start looking.
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470uf ok but contains inductance, use a .1uF next to the audio cct.
« Last Edit: January 07, 2013, 07:18:23 pm by LarryD » Logged

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