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Hot Swapping Headphone Jack - Temporary Shorts During Insertion - How To Remedy?

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Jattus

New Member
Hey guys,
I have a 3-wire temperature sensor (DS18B20) wired up to a headphone jack. I have the corresponding receptacle on the PCB. If the device is powered off before insertion of the plug, everything is fine.
However, inserting the jack while the device is running causes the device to reset. This is because during the insertion of a headphone jack, there are temporary shorts that occur:
* Sleeve gets shorted to the ring
* Sleeve gets shorted to the tip
* Ring gets shorted to the tip
Once its fully inserted nothing is shorting with one another.

The device is resetting because when a power rail gets shorted to ground, it pulls too much current and the voltage regulators that are upstream shut-down until the high current is removed.

You might be wondering, why not use the version of receptacle/jack that has the built in switches? The switches indicate when the plug is inserted in all the way, at which point I could activate the power and problem solved right? I cannot do this because the user has the option of using an audio extension cable... so plugging/unplugging at the other end of the cable would cause the temporary shorts and the problem would remain.

Another note: I cannot switch to a different style of plug, it has to be a 3 wire stereo audio jack.

I had an idea of using an LDO voltage regulator (such as the "TC1014" which is a 50mA regulator) using this as a current limiter. I was thinking I could use one of these on the 2 red dots I indicated in my schematic. My idea is that when this gets shorted to ground, this will cause an over current situation so the TC1014 will just shutdown and no current will flow.

Would this work? Is there a better solution? I am pretty stuck on this so any help is greatly appreciated, thanks!

Here is a schematic for reference:
hot_swap_question2.jpg
In this schematic going from right to left, the rectangular box is the "sleeve", the middle connector is the "ring", and the last connector is the "tip" (in this case, this is the data line that is being pulled high to 3.3V).

And here is the datasheet to the audio jack/receptacle (I am using the "SJ1-3523N" version):
http://www.mouser.com/ds/2/670/sj1-352xn-series-535548.pdf
 

Externet

Well-Known Member
I would make short adapting extensions with XLR male+female connectors. And those to be used as disconnect/connect without shorting.
The audio jack/plug will always stay inserted. The probe cable connector will have then, a XLR plug/jack. No alterations to your original equipment.

probecable----------------------connector-->>--connector-------XLRm---->>----XLRf------connector-->>panel connector

"Connectors" are your current audio type. Blue are the adapting short extensions. Red is now the troubling connection.

There is also miniature XLR if preferred.
Both sizes ----> http://www.kvconnection.com/v/vspfiles/photos/K-X3MMX3M-15-2.jpg

Solved ? ;)
 

Jattus

New Member
I would make short adapting extensions with XLR male+female connectors. And those to be used as disconnect/connect without shorting.
The audio jack/plug will always stay inserted. The probe cable connector will have then, a XLR plug/jack. No alterations to your original equipment.

probecable----------------------connector-->>--connector-------XLRm---->>----XLRf------connector-->>panel connector

"Connectors" are your current audio type. Blue are the adapting short extensions. Red is now the troubling connection.

There is also miniature XLR if preferred.
Both sizes ----> http://www.kvconnection.com/v/vspfiles/photos/K-X3MMX3M-15-2.jpg

Solved ? ;)
Thanks for the response Externet,
But as mentioned above, "Another note: I cannot switch to a different style of plug, it has to be a 3 wire stereo audio jack."
Everything has to be these standard audio connectors, so I am looking for a solution that can accommodate them.
 

MikeMl

Well-Known Member
Most Helpful Member
If Tip was wired to +5V instead of Ring, then I dont see how 5V can ever get shorted to gnd?

This reminds me of how an aircraft mic jack gets wired. PTT is wired to TIP (it has +14V or +28V through a relay coil resistance on it), Mic is ring, Sleeve is common. No voltage backfeeds to Ring, and the transmitter is not accidently keyed as the plug is inserted...
 

spec

Well-Known Member
Most Helpful Member
Hy Jattus,

Which State are you at?

Here is an approach that should do your job.

spec

2016_05_23_ETO_DS18B20_TEMP_SENSOR_5V_SUPPLY_VER1.png
 

dr pepper

Well-Known Member
Most Helpful Member
I had the same problem with a project, just swap ring and tip, so long as the sensor connection doesnt mind being grounded.
 

fezder

Well-Known Member
ouch, nasty situation....reminds of when I was looking around in local household appliances store, there staff was placing some HiFi-stereo system to live when *snap*. I asked about it and for some reason during setting plugs to their places, some random short occurred and of course device was ON during set-up. They were quite sweating about whether It'll go under warranty or not, it wasn't cheap system....
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Historically the UK Post Office (pre-BT) telephone system used jack plugs - but they used special ones that didn't short out as you plugged them in, for similar reasons to this thread.

However, while they were 6.3mm, they were incompatible with normal jack plugs.

We actually used them for our soldering irons at work - with 24V AC feeds to the benches, and 24V temperature controlled soldering irons. We don't use them any more, as Antex discontinued the 24V range :(
 

dr pepper

Well-Known Member
Most Helpful Member
I remember those, used for power supplies amongst other things, some were 5 pin, I think I have a 50v solder iron somewhere with a 1/4 jack on the end.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I remember those, used for power supplies amongst other things, some were 5 pin
Antex irons were 5 pin DIN (and still are), we removed the DIN and fitted a BT jack - obtained from a friend who worked at BT (and who sadly died last week :()

I think I have a 50v solder iron somewhere with a 1/4 jack on the end.
That's what BT used 'back in the day'.
 

dr pepper

Well-Known Member
Most Helpful Member
It is bt, well actually gpo.
I had a summer 'job' when I was at school, 'helping' out in the local telephone exchange, I even got some of the scrap gear when they ripped out the old mechanical stuff when they went transistor.
 

Jattus

New Member
Hy Jattus,

Which State are you at?

Here is an approach that should do your job.

spec

Thanks again guys for all the help!
I am in Colorado if that is what you are asking.

So the 220 ohm resistor did the trick, couldn't believe it was so simple of a solution.

Is this correct by the way? During a short it will pull only 22mA, and the 220 ohm resistor will dissipate about 0.113 watts?
I=V/R
I=5/220
I=0.0227

P=VI
P=5*0.0227
P=0.113 watts
 

spec

Well-Known Member
Most Helpful Member
Thanks again guys for all the help!
I am in Colorado if that is what you are asking.

So the 220 ohm resistor did the trick, couldn't believe it was so simple of a solution.

Is this correct by the way? During a short it will pull only 22mA, and the 220 ohm resistor will dissipate about 0.113 watts?
I=V/R
I=5/220
I=0.0227

P=VI
P=5*0.0227
P=0.113 watts
No probs Jattus,

Yes that what I was asking- it is interesting to know where people are. It also helps with mains supplies safety standard and access to components.

Sometimes solutions are simple, other times not so simple. :nailbiting:

Your calculations are correct.

The capacitor is for decoupling and can be any ceramic capacitor 100nF or larger, but not the very small surface mount types.

spec
 

ChrisP58

Well-Known Member
Most Helpful Member
Spec beat me to it with the resistor idea. The operating current of the DS18B20 is only 1.5mA max, so you could use a higher value of resistance if you're concerned with it's power dissipation. Just as long as the voltage at the part is at least 3V. But don't forget to add some margin for the resistance of the unknown cable length.

And while we're talking cable length, if the total cable length is more that a few feet (or inches, for many parts,) then the cap should be close to the DS18B20. Or better yet, one at the jack and one at the sensor.
 
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