3.5mm stereo jack causing shorting

Got a project all together, really pretty (PCB, LCD, acrylic plate coming). Just one problem.

I have photo interrupters connected to the PCB with 3.5mm stereo cables and jacks on both sides. When I connect or disconnect the plug on the PCB side (rear is ground, middle is signal - high for unblocked interrupter, tip is supplying 5V to the interrupter), I get short circuits. Arduino powers off for a moment and windows makes the USB unplugged sound effect. The LCD resets to a row of black blocks. If I try to carefully remove the plug while forcing it on the side, sometimes I don't get shorting. I wonder if stereo plugs can get shorting just by themselves. But forcing it to lean on top or bottom sides will get shorting. Maybe I was doing something silly.

Parts I used: photo interrupter: http://www.sparkfun.com/commerce/product_info.php?products_id=9299

interrupter PCB: http://www.sparkfun.com/commerce/product_info.php?products_id=9322

stereo jack: http://www.sparkfun.com/commerce/product_info.php?products_id=8032

The jack on the interrupter side is mounted on the side of a chocolate box never unplugged.

Just a side note. When I misconnected this interrupter (swapped 5V and GND), I did release some of the precious smokes residing in the interrupter but after the problem was corrected it still works fine (enough smoke left inside to function).

Thanks for replying!

That's the nature of a jack - almost guaranteed to short soemthing to something else.

You might want to ditch the 3.5mm plugs/jacks and go with RJ11 plugs and jacks; with the “concentric” nature of the plugs you are using causing shorts, the isolated and parallel nature of RJ11 might suit your application better.

The good thing is that you can generally find a lot of surplus RJ-11 or RJ-12 things, jacks in all veriaties and cable in any length for a bargain. They are very robust - meant to be stepped onto..

Issues I encountered: - The wires are very thin and unflexible, many broke after short time until I found a good soldering technique. - The contact resistance of a pair of crimped plug/jack is high, I measured around 2 Ohms. Which can add up to 8 Ohms for the whole path +5V and back to Ground when used as power supply... This is not negligeable

Thanks guys. If a stereo jack shorts so easily, then what do computers do to avoid catching fire when a head phone is plugged in?

Yeah, I could choose RJ11 but what about bargan cables? I see a lot of 2-wire cables. I need at least 2 wires for 5V, gnd, and signal. Thanks again.

Thanks guys. If a stereo jack shorts so easily, then what do computers do to avoid catching fire when a head phone is plugged in?

Such cables and connections involve an audio signal only - not power...

Yeah, I could choose RJ11 but what about bargan cables? I see a lot of 2-wire cables. I need at least 2 wires for 5V, gnd, and signal. Thanks again.

If you want a four-wire cable, you will probably have to make it yourself using a crimp tool, RJ11 plugs, and 4-conductor telephone wire. Fairly cheap and easy to do, just like building your own cat5 patch cables.

I see a lot of 2-wire cables. I need at least 2 wires for 5V, gnd, and signal.

I have a lot of 4-wire cables here and in surplus shops. They are arount 20 cents/m. Maybe they will be called RJ-12. There is a steady confusion about that. They come with 6 pin plugs, where only the middle 4 are wired. This is known as 6p4c. For unclear reasons these seem to be cheaper than 4p4c types.

Thanks cr0sh. I will have to make the transition. Now need a crimper and a whole lot of space for a big roll of phone wires.

RJ 12 is the jack size (12mm) like a RJ45 is 45mm (commonly used with 8 pin connectors known as ethernet cables) I should note that RJ11 is common telco connectors in the USA, and that the size is of the inside of the female socket (ie a RJ11 male plug is around 9mm)

you can get all sorts of wire that will work with RJ connectors, watch out for pre made phone cables though, at least here in the US the telco connectors are reverse on one end from the other

crimpers are cheap and usually handle both 11 and 45, so you can make your own phone cables and network cables, odd sizes (like the 80whatever on my IBM keyboard) will run you money, but its not necessary

also as crash touched on your computer doesnt catch fire because your dealing with 0-0.7, maybe 1v, usually isolated jack squat current audio signals

but phono jacks do decent in rotary applications due to the same reason they short, its spring loaded

Thanks Osgeld. I will make the switch now that I have got enough information here.

deSilva, are you talking about the pins on the female jack? Are you soldering them on a perf board or a PCB? I plan to design PCB with exact pin locations. Will I still have trouble soldering the pins? Thanks.

No. That is fine. In my situation a lot of devices had to be connected with different generic connectors. I first wanted to connect RJ jacks to them, to allow a standard wiring, but to reduce cost and effort I then tried to directly solder a reasonably long pigtail with an RJ plug to it.
Hower this failed; the telephone wires are not made for this, but for being crimped to plugs only, so it seems.

A workaround was to solder 10 cm more flexible wires (AWG20 …22) to the four lines, protected by heat shring tubing - effort saving, indeed :frowning:

I already mentioned the high transition resistance of the plug/jack combination, so take care with “high” current (>20mA), voltage and ground (!) will shift.

deSilva(congrats! you just became god!) Thanks for the tip. I didn't get it in time. Wasted a cheap phone cable as a result. The wires are impossible to strip. I will look around for other connectors so I don't have to worry about such resistance that you mentioned.