Caution: USB debugging plug-in

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Caution: USB debugging plug-in

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NXP Employee
NXP Employee

All,

Just FYI-- I had something happen yesterday while debugging that is very likely to happen to others.  When plugging in the mini-USB plug into the FRDM-KL25 board (I unplug/plug often while debugging), I accidentally missed and the plug hit the lower part of the FRDM-TFC board.  It caused a short and a little smoke!

Turns out I likely shorted the underside of the ground and Vbattery terminals to the servo.   Thankfully I pulled it away fast enough to not cause damage.

I've added some electrical tape on the underside of the FRDM-TFC board just in case in that area.

Here's a pic highlighting the possible short you could do:

IMG_20130929_203825---edit.jpg

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NXP Employee
NXP Employee

Since the steering servo connection is directly above the debug USB connector, there is a series 1Ohm resistor (R8) between the positive battery terminal and the middle connection of the servo header. The resistor will probably die before any traces on the board if the header is shorted. Still, shorting the pins should be avoided...

In any case, if your servo is still working, R8 is probably still fine.

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NXP Employee
NXP Employee

David,

Yep—R8 is what blew out when I had a crash a couple of weeks ago. Talking to someone else this also happened to them after a crash, R8 burning out. Wondering if a future rev of the board could fix this.

Daniel

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NXP Employee
NXP Employee

A larger wattage resistor might help, but then does that make the servo more likely to fail?  I'm not sure.

One way to do it might be to use a regulator with a thermal shutdown, which in theory, should provide protection without having to replace a resistor and without risking killing the servo.

But, resistors are cheap, easy to replace and it does not happen all that often...

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NXP Employee
NXP Employee

Daniel,

Thank You !

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