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Author Topic: AC->DC wall wart buzzing interference  (Read 1614 times)

trials_modder

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AC->DC wall wart buzzing interference
« on: July 30, 2006, 12:33:49 PM »

Hi

I connected a 12V wall AC to DC adapter to a 5 volt voltage regulator, which in turn was connected to my FM transmitter. It caused the transmitter to transmit a buzzing sound in the background of whatever music was playing. HOw do I remedy the problem? Hooking the transmitter up to the USB's 5v rail, or batteries does not cause the problem.
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blafrisch

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Re: AC->DC wall wart buzzing interference
« Reply #1 on: July 30, 2006, 03:52:43 PM »

What is the required input voltage for the transmitter.  I'm assuming battery powered is done with AA batteries or some type of 1.5V battery.  5V is not a multiple of 1.5V.  I'm going to venture a guess and say it takes 3 AA batteries (4.5V).  That would mean you are overpowering it and working all too hard with a voltage regulator.  They make 4.5V wall warts.  Now if I'm wrong, correct me, but I think you need a 4.5V wall wart.
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viridius

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Re: AC->DC wall wart buzzing interference
« Reply #2 on: July 30, 2006, 04:54:55 PM »

Shouldn't be causing the buzzing.  Try slapping a 0.1-10uF capacitor across the power leads and see if that clears it up.
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trials_modder

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Re: AC->DC wall wart buzzing interference
« Reply #3 on: July 30, 2006, 07:38:27 PM »

Cool. I just stuck a 50v 1 uF electrolytic capacitor across the voltage leads and the buzzing just went away! I love it when problems are this easy to resolve. Any idea how what I just did fixed the buzzing?
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viridius

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Re: AC->DC wall wart buzzing interference
« Reply #4 on: July 30, 2006, 09:40:02 PM »

The wall wart probably wasn't putting out the cleanest DC signal.  If you were to hook it up to a scope, you'd see a trace around 5 volts that went up and down a bit.  The capacitor you put in there opposes any change in voltage, so your supply to the transmitter is cleaner.
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