Re: Audio switch with LED

On Aug 12, 5:45 pm, Cobus Kruger <spamwontw...@xxxxxxxxxxxxx> wrote:
Hello,

I fear that to explain the full extent of my problem, I would need to
post under a false name to spare the embarrassment :-)

To simplify, I have built a couple of boxes to switch between multiple
audio/video sources to a single output and they all work fine. What I am
trying to do now, is build a box that can switch my PC's audio output to
one or more destinations throughout the house. This seems simple enough.
The problem comes in with the LED I am trying to add.

I wanted to add a LED for each line so that I can easily tell how many
output lines are active. To drive the LED, I need a 3V battery (feel
free to correct me wherever I go wrong :-)). I then got a switch where
input is connected to the middle terminal, and output can be either of
the terminals beside it (3 terminals in total).

To prevent current to the LED from affecting the audio signal, I
cleverly decided to place the switch on the ground wire. This however,
works fine with the LED, but the sound seems to play just fine *without*
the ground wire.

So, I have a couple of questions where I would dearly appreciate any
good answer:
1. Why is ground not used for audio? Does the recipient device have a
common ground or is there a different answer?
2. Why does the current from the battery not affect the audio signal at
all? This is the one that stumps me. I expected lots of noise, but it
sounds just the same. Or am I not listening close enough?
3. Where should I put the switch now?
4. Lastly, what is a good amount of current to drive a regular 3mm LED?

Eagerly awaiting responses...

Regards,

Cobus Kruger

From your description, I'm not sure how you're trying to wire in your
LED. But don't try to drive an LED from your audio circuit. Change
your switch to a 2 pole switch (one pole for audio switching and one
pole for LED lighting). Check the specs for your LED, but a typical
LED needs about 20 mA. Size your resistor accordingly.

BRW

.

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