USB device interfering AM radio

I just discovered this. And I also found that the AC to USB power
adaptor does not have a metal ground pin.

So would this AM interference be gone after getting a better AC to USB
power adaptor?

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If that is where it's really coming from? You could have a bad insulator
out side your place, on the lines or, some equipment else where causing
it. You can tell better if you operate it via battery. If the noise
goes away, then you need a line filter for your plug.. Other than that,
if that does not take care of it, you have a cheap set up.

If it really is coming from your outlet power, you could use a 1:1
transformer to isolate it. I've found that to work very good. But I am
thinking that maybe you are operating a cheap switching supply and the
radio is picking that up..

Jamie

 

it. You can tell better if you operate it via battery. If the noise

Could the outside mesh shield of USB cable contain the noise?

Line filter? Is it a chip or a circuit? I am not a EE guy.

It's just a cheap AC to USB power adaptor.

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This is the simple circuit.

AC ---> AC-to-USB power adaptor
---> 3-feet USB cable (5V)
---> 2x100ohm resistors
---> 2 LEDs in parallel

The AM/FM radio is about a feet away the circuit.

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From your description, I assume your circuit is like this:

+5 ---+---[R]---[LED1]---+---Gnd
| |
+---[R]---[LED2]---+

If your adapter is truly providing 5 volts, and those are
standard LEDs, you may cook them. They are running near
the max with 100 ohm resistors.

It would be better for the LEDs if it was like this:

+5---[R]---[LED1]---[LED2]---Gnd

That would cut the LED current from about 32 mA to about 15 mA.
and they would still be plenty bright.

As to the noise, I would not be surprised to find crappy
electronics (cheap USB adapter or whatever) causing it,
so replacing the adapter with a better one might cure it.

Ed

 

+5 ---+---[R]---[LED1]---+---Gnd

No. It's this:

+5 ---[R=100ohm]--+--[LED1]--+
| |
GND ---[R=100ohm]--+--[LED2]--+


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No, it can't be like that - there would be no current
through the LEDs. The way it's drawn, the LEDs have a
short circuit across them (the vertical line between the
resistors and the LEDs). If that line was not there,
and the LEDs are in series with the correct polarity,
it would work fine. You'd have about 14 mA through the
LEDs, and they would shine nicely. They would not be
at full brightness, but they would not be too dim.

Maybe it's really wired like this:

+5 ---+---[100R]---+---[LED1]---+
| | |
+---[100R]---+ |
|
Gnd -------------------[LED2]---+

That would give you about 28 mA through the LEDs which
is still higher than I like, but should be ok with
LEDs rated for 30 or 35 mA max.

Ed

 

+5 ---+---[100R]---+---[LED1]---+

My mistake drawing the diagram. Thanks.

+5 ---[R=100ohm]--+----+
| |
LED1 LED2
| |
GND ---[R=100ohm]--+----+

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Not a good idea. The LEDs are unlikely to share current evenly. Use one
ballast resistor for each. It doesn't matter which side it's on.

 

Not a good idea. The LEDs are unlikely to share current evenly. Use one

Already soldered, don't wanna change it. Next project...

http://img843.imageshack.us/i/gn002withleds.jpg/

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No one can help you if you don't want to do it right.