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# What type of signal is coming from a 3.5mm audio plug? Answered

does it create alternating DC voltages? (for example, alternating from +50mV to +200mV)
or does it create only AC voltage (without standing DC) (for example, alternating from +100mV to -100mV) ?

(when referred to the 'ground' wire on the 3.5mm plug which is the thickest connection, closest to the wire itself).

If it's only AC without standing DC on it, then how come the TEA2025B microchip can work fine when connecting it directly to the input pin?
because that would mean the input pin would have no problems with negative voltages applied to it... (with the negative voltages, I mean something like -100mV, coming from the AC input signal).

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## Discussions

can anybody tell me pls that by the output of that jack we are able to blink led or not or we can send it as remote or not??? and if yes then how???

First thing is what are you considering i the jack is for head phones then there are three wires one of golden color and two of red blue or any other color the golden wire is the negative and the two colored wires are for the the positive terminals .( left and right audio ) in headphones case they emit and very very low voltage of 0.5 to max 2.00 volts and it's for is dc analog means the current is dc but it's analog and it's frequency depends on the type of sound you are listening.
if you will supply 2volts constant to the sound will be of same frequency and less volume! and when you are considered about a mic jack it has only two wires coming out when you will cut it's wire in this case when you speak something the two wires get connected with each other in the frequency you are speaking it's just like a switch which switches on and off as the frequency you are speaking!
i hope this will solve your problem! see ya !

"Teachers" are not EEs. Teachers usually have only a bare minimal grasp of the subject.

AC, with a DC offset. Has it gone non-zero Fourier coefficients ?

It depends on how fussy you want to be.
The classic LM3915 will accept negative inputs, but obviously won't display them - you can see average and peak levels fairly easily.

Next, you can get away with a common emitter amplifier, coupled, via a diode to the input of the 3915. That works for one device.

Failing that, make a "perfect rectifier" using an op-amp and a couple of diodes.

Take a look at the datasheet for the LM3915 - I am sure it is discussed in enough depth to work out something yourself..

ok, you CAN have negative DC current. Its very possible. Many amp datasheets ask for a +12v power supply, as well as a -12v supply. Trust me, ive tried using these.

AC current simply means that the current switches between + and - really fast. There IS a "zero cross". This can be 1v and -1v, or anything, as long as it alternates.

Pulsating current is direct current, but with changes, eg, 5v, boosted to 12v, then down to 5v again.

You can have negative DC pulsting current, for the same reasons you have negative DC and pulsating current.

You can also have Variable current, which is pretty much just any voltage that can change to any voltage.

When in doubt, Wiki.

A
lso, for all others here, I am sorry if this info is misleading/wrong. If it is, please correct so I can better understand :)

Define "0"

It is an arbitrary reference point, and can be where ever you like.

Yes, because you really don't want the very very high input impedance of your amp as the terminating impedance of your input - - its an invitation to admit noise to the circuit and/or RF pickup.

http://en.wikipedia.org/wiki/Line_level

from the looks of it it's ac based around 0v ground

NO !
Its AC coupled - DC can't pass through the capacitor. The parallel resistor between the coupling cap and ground defines the "input" resistance.

Steve

Then its AC !

You CAN have AC, with a DC offset.

You can't HAVE "alternating DC" Alternating direct current is a complete non-sequitur !!!

Looking at the device datasheet, the input is always capacitively coupled, so the AC sound signal is coupled into the (presumably DC offset) input.