How does the microphone jack know that a microphone is plugged in?

[Timur Tabi]

I have a 1/8th inch headphone/microphone jack, and my device thinks
that my headset is always plugged in, even when it isn't. I presume
that there is a physical or electrical sensor either in the jack
itself or in the device. A google search revealed nothing. Can
someone explain to me how this works? I need to know whether
replacing the physical jack could fix it.

 

[Tim Wescott]

I have a 1/8th inch headphone/microphone jack, and my device thinks that
my headset is always plugged in, even when it isn't. I presume that
there is a physical or electrical sensor either in the jack itself or in
the device. A google search revealed nothing. Can someone explain to
me how this works? I need to know whether replacing the physical jack
could fix it.

There's an electro-mechanical 'sensor' -- normally there's a little
switch (or a pair of them for a stereo jack) that are normally closed,
but get pushed open when a headset is plugged in. Normal practice is to
just wire the sound through the jack, to the speaker.

I keep saying 'normal' here because if your device is actually
_indicating_ that there's something plugged in, then they're doing
something more sophisticated than just switching the audio after all else
is said and done. If this is, indeed, the case, then something else
could be broken.

Try replacing the jack, see if it helps.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

 

[Eeyore]

I have a 1/8th inch headphone/microphone jack

Actually it's 3.5 mm !

Graham

 

[Timur Tabi]

There's an electro-mechanical 'sensor' -- normally there's a little
switch (or a pair of them for a stereo jack) that are normally closed,
but get pushed open when a headset is plugged in. Normal practice is to
just wire the sound through the jack, to the speaker.

So all this switch does is to open the circuit? What's the point in
that? Without the headset plugged in, isn't the circuit already
closed?

 

[Tim Wescott]

So all this switch does is to open the circuit? What's the point in
that? Without the headset plugged in, isn't the circuit already
closed?

It opens the circuit to the speakers, or sometimes it opens the circuit
between the drive amplifier and the final, so that with headphones you
just get the output of the drive amp.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

 

[Timur Tabi]

It opens the circuit to the speakers, or sometimes it opens the circuit
between the drive amplifier and the final, so that with headphones you
just get the output of the drive amp.

Sorry, I still don't understand. There are only three cables going to
the jack from the device: ground, left channel, right channel.
Without the headset plugged in, how can any circuit be open, even
without a switch?

 

[DJ Delorie]

Sorry, I still don't understand. There are only three cables going to
the jack from the device: ground, left channel, right channel.

If you know there are only three traces connecting to the jack inside
the device, then it's most likely measuring the impedance of whatever
you plug in, to try to guess what it is.

 

[Michael A. Terrell]

Actually it's 3.5 mm !

Graham

Only where it doesn't matter.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[David Harmon]

Actually it's 3.5 mm !

Graham

Only where it doesn't matter.[/QUOTE]

Is that why those crappy jacks don't make contact half of the time?

 

[Michael A. Terrell]

Only where it doesn't matter.

Is that why those crappy jacks don't make contact half of the time?[/QUOTE]


The original 1/8" plugs and jacks were very good quality, but the
imported crap is just that. I have Switchcraft 1/8" connectors that are
almost 40 years old, and still work like the day I bought them.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[robb]

I have a 1/8th inch headphone/microphone jack, and my device thinks
that my headset is always plugged in, even when it isn't. I presume
that there is a physical or electrical sensor either in the jack
itself or in the device. A google search revealed nothing. Can
someone explain to me how this works? I need to know whether
replacing the physical jack could fix it.

How does your device indicate the headset is connected ?
is there a LED or a lcd display indicator ?

anyways in the simplest method...
the headset jack is a set of contacts installed in series with
the output lines to some external output like speaker out.
inserting a headset plug into the headset jack simply moves the
contacts apart and the plug intercepts/redirects the output
signal to the headset.

Removing the plug allows the contacts to spring back into their
series connection and the signal is no longer intercepted and
will continue on to the external output.

if one of those contacts breaks or is blocked by some
scata/crud/gunk then the jack will not be able to reset itself
into a series connection and the signal stops at the headset
jack.

that is the mechanical method.
hth
robb

 

[z]

Sorry, I still don't understand.  There are only three cables going to
the jack from the device: ground, left channel, right channel.
Without the headset plugged in, how can any circuit be open, even
without a switch?

wait a minute, what are we talking about here? first you said
headphone/microphone jack, now it's left channel and right channel?

 

[Norman Webb]

Timur Tabi wrote in message

I have a 1/8th inch headphone/microphone jack, and my device thinks
that my headset is always plugged in, even when it isn't. I presume
that there is a physical or electrical sensor either in the jack
itself or in the device. A google search revealed nothing. Can
someone explain to me how this works? I need to know whether
replacing the physical jack could fix it.

How does your device think the earphones are plugged in?
I presume your main speakers aren't working.

The "normal" wiring is for the wires for the speakers to go via the earphone
jack. The earphone plug has terminals which open when the earphone plug is
inserted thus cutting off supply to the speakers.

These contacts may be bent so that when you remove the earphone plug they
stay open.