Unknown component identification

[Jiggy-Ninja]

http://www.adafruit.com/blog/2012/05/25/handy-arduino-r3-pinout-diagram/

What is the component just below the USB connector, and to the left of the SOT transistor? I've seen something like this on a few other boards, but I can never place exactly what it is.

 

[Kholdstare]

Not very sure, as it can be either resistor or capacitor. But my bet is on capacitor.

 

[AlephZero]

The label looks like "501K" whcih would not be a standard value capacitor or resistor

I wouder if it's this (quote from http://arduino.cc/en/Main/arduinoBoardUno)

The Arduino Uno has a resettable polyfuse that protects your computer's USB ports from shorts and overcurrent. Although most computers provide their own internal protection, the fuse provides an extra layer of protection. If more than 500 mA is applied to the USB port, the fuse will automatically break the connection until the short or overload is removed.

If the labelling convention is the same as for capacitors, the "501" would mean "50 foloowed by one zero", i.e. "500" which matches the stated fuse rating.

There are links to the schematic and board design from that web page, so they should give you the answer.

 

[schip666!]

I believe it is a fuse on the USB power in.
The schematic shows an F1 500ma fuse on the XUSB line (lower right corner):
http://arduino.cc/en/uploads/Main/arduino-uno-rev2-schematic.pdf
And I think I can make out the F1 label, in magenta between the two components, on the layout picture here:
http://balau82.files.wordpress.com/...-arduino_uno_ref-brd-eagle-5-10-0-light-1.png

 

[Kholdstare]

Hmm. Did not think about fuse.

 

[dlgoff]

I was thinking some kind of optocoupler. e.g.

https://docs.google.com/viewer?a=v&q=cache:g9zMFbYGSE0J:www.profesormolina.com.ar/electronica/datasheets/downloads/hcpl_0452_500_501.pdf+&hl=en&gl=us&pid=bl&srcid=ADGEEShfJo9963jqRjyJjFzvObPVUIPl7K8FZMhfk9uhwna8ezn5Qtl5HkT4tRyto70ixwIE9lsRObCfSoHc-boxotWLIAQMSWB_MOLrBHu3yAE8OP7GEcm03gtDHNwUxUrqDQqHdFlA&sig=AHIEtbQG_UkxGlO2K9LGkb7GUVCoYy-grA

 

[Studiot]

Yes it's a fuse.

See here

http://arduino.cc/forum/index.php?topic=107605.0;wap2

 

[jim hardy]

Good find Studiot

it's a ptc thermistor...
great idea - a fuse that resets itself after short is removed!


Only way to go when it's soldered in !

http://www.bourns.com/data/global/pdfs/Bourns_2010_industrial_PTC_appnote.pdf
http://www.bourns.com/data/global/pdfs/bourns_auto_short_form.pdf

 

[Jiggy-Ninja]

I was thinking some kind of optocoupler. e.g.

https://docs.google.com/viewer?a=v&q=cache:g9zMFbYGSE0J:www.profesormolina.com.ar/electronica/datasheets/downloads/hcpl_0452_500_501.pdf+&hl=en&gl=us&pid=bl&srcid=ADGEEShfJo9963jqRjyJjFzvObPVUIPl7K8FZMhfk9uhwna8ezn5Qtl5HkT4tRyto70ixwIE9lsRObCfSoHc-boxotWLIAQMSWB_MOLrBHu3yAE8OP7GEcm03gtDHNwUxUrqDQqHdFlA&sig=AHIEtbQG_UkxGlO2K9LGkb7GUVCoYy-grA

I wasn't referring to an IC.

I believe it is a fuse on the USB power in.
The schematic shows an F1 500ma fuse on the XUSB line (lower right corner):
http://arduino.cc/en/uploads/Main/arduino-uno-rev2-schematic.pdf
And I think I can make out the F1 label, in magenta between the two components, on the layout picture here:
http://balau82.files.wordpress.com/...-arduino_uno_ref-brd-eagle-5-10-0-light-1.png

This makes perfect sense. I had tried to look at the schematics, but all the various undifferentiated boxes of the Eagle (I assume) schematic left me a bit confied about what was what.

I had pulled out my multimeter and did a couple continuity tests, and found that one end is connected to one of the USB pins, and the other goes to the middle pin of the SOT MOSFET, which I had assumed was the gate, and looked around that area in the schematic.

Lesson: Don't assume pinouts! Check the damn datasheet! You know the saying.

The only PTC devices I've seen so far are the through hole ones that look like a large ceramic cap with the leads kinked in a little at the top. I had no idea they looked like this in SMD form. Though it makes sense since it would need a large surface area to dissipate heat from.