I searched on YouTube and Google about an easy way for finding the base, collector and emitter of transistor's pins, and I found this link: http://www.youtube.com/watch?v=DJ9mg7b_SiA

Is this method right? and if not, can anyone provide for me a better way?

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    \$\begingroup\$ Better way? Google the transistor part number and find the datasheet. \$\endgroup\$ – Passerby Jul 24 '13 at 20:46
  • \$\begingroup\$ @Passerby Do I always need to search for its datasheet? I mean is there a way to do it Manually? like using Multimeter? \$\endgroup\$ – Psycho 4 Physics Jul 24 '13 at 20:48
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    \$\begingroup\$ Step 1: Check that you have base, collector, and emitter and not, say, gate, source, and drain. \$\endgroup\$ – Ignacio Vazquez-Abrams Jul 24 '13 at 20:56
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    \$\begingroup\$ @Psycho4Physics While you "might" be able to figure it out with a multimeter, that will not keep you from needing the datasheet. The datasheet gives you much more information than just the pinouts. So while you might be able to do it with a multimeter, since you need to get the datasheets anyway you might as well get the pinouts from there too. \$\endgroup\$ – user3624 Jul 24 '13 at 20:56
  • \$\begingroup\$ Always need to? No. But you asked for a better way, and that is the best way. \$\endgroup\$ – Passerby Jul 24 '13 at 20:57

There are many ways (sorted starting with easiest):

  1. If you know the part number - Google it
  2. You do not know the part number, but the package is standard (TO-220 for example) - you can find legs specifications in package's spec (or just find a datasheet of any other similar transistor in this kind of package). Some standard packages are symmetric though :(
  3. Diode mode measurement (as seen in the video)
  4. Resistance mode measurement (instead of measuring diodes' forward voltage, you measure the resistance between pins)
  5. If none of the above worked (or you just don't have a multimeter) - you're dead in the waters

EDIT: while it is nice as a theoretical example, in practice you will never work with an unknown component (unless you're really desperate), therefore you'll always have datasheet.

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  • \$\begingroup\$ There is in some Multimeters something called (hFE)to know your resistor's pins. \$\endgroup\$ – Psycho 4 Physics Jul 24 '13 at 21:09
  • \$\begingroup\$ You meant transistor's pins, right? This mode actually measures transistor's current gain. While it can be used to determine transistor's pins, it is much simpler to use methods 3 and 4 from the above list. \$\endgroup\$ – Vasiliy Jul 24 '13 at 21:15
  • \$\begingroup\$ Sorry for the mistake.So if I was very "desperate" , do you recommend me to use what is in the Multimeter? \$\endgroup\$ – Psycho 4 Physics Jul 24 '13 at 21:17
  • \$\begingroup\$ I've never seen a multimeter which can measure transistors' gain, but has no diode forward drop mode. If you happen to have such a device - go for gain measurement. Do you really mean to say this question isn't theoretical? \$\endgroup\$ – Vasiliy Jul 24 '13 at 21:21
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    \$\begingroup\$ Practically, I don't see any reason to work with a component when you don't have its datasheet. Go and buy another transistor - its the best advice I can think of. \$\endgroup\$ – Vasiliy Jul 24 '13 at 22:40

A nice tool is the AVR transistor tester (translation here) which can identify the type of component (NPN, PNP, FET, Diode and some more), tells you which pin is which, and also does some measurements (e.g. hFE).

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