What type of signal is coming from a 3.5mm audio plug?
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).
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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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 !
so the amplifier Can work with negative voltages?
Or did you mean DC coupled so that a DC voltage gets superimposed on the AC voltage to get alternating DC?
You CAN have AC, with a DC offset.
I'm 100% sure that my teacher said that you can only speak of AC if there is a zero crossing (change from positive to negative).
Signals that don't cross zero are called DC signals here and if they are not constant, they are called variable DC voltages
(that's how it's like in my country)
;-)
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.
Also, for all others here, I am sorry if this info is misleading/wrong. If it is, please correct so I can better understand :)
It is an arbitrary reference point, and can be where ever you like.
Do you also know how they do that? because it would be logic to connect the 'GND' connection from the 3.5mm plug to a non-0V connection from the IC. for example something like 300mV but that connection is connected to the ground so I don't understand how they add a DC voltage to that input signal...
Its AC coupled - DC can't pass through the capacitor. The parallel resistor between the coupling cap and ground defines the "input" resistance.
Steve
So that means AC voltage enters the IC. --> negative currents enter the IC's input too at the negative alternations.
This is why it looks so weird.
and is the input resistor always necessary?
if I just amplify the signal, it wouldn't be a good VU meter, because the negative alternations will then lower the output voltage and that's not good.
Amplifying the amplitude or the peaktopeak voltage of the imput signal would be good because that is proportional with the volume of the sound.
How can I do that with this IC? it would be good to rectify the input signal, and then amplify it, but I can't rectify a 100mV signal with diodes.
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..
from the looks of it it's ac based around 0v ground
http://en.wikipedia.org/wiki/Line_out_(signal)
what output voltage does a "quiet" signal give? 0V or 300mV?