Problem about transistor?

Question

How can i get to know about collector and emitter side of a commercially available transistor without using multimeter

Answer 1

From your question I presume you know which terminal is the Base and you know that it is an NPN or PNP type of transistor.
To find out which lead is the Collector and which the Emitter is very easily done.
Assuming that it is an NPN type :
Label the 2 leads that have to be identified as 1 and 2.
Connect 2 to the + and 1 to the - of a 12 volt supply.
Connect a 12k resistor between +12v and base. (to drive ~1 mA into the Base)
Watch what the current through the lead 2 is. (say 50mA)
Repeat the above process with 1 connected to +12 and 2 to the -. and watch the current (say 2 mA)
That connection which gives the higher current is the proper connection and that terminal which is connected to the +12v is the Collector.
One can identify the C and E terminals of a transistor this way without using a multimeter. Take care not to send base current for too long a period as the transistor will overheat and be destroyed.

Answer 2

You can check a cross reference manual or check the specs on line for a diagram of the pin layout.
Even with a meter, you will be only able to accurately determine where the base is - as it is biased the same to both the collector and emitter.
Or, you can purchase a very inexpensive transistor tester with three leads which are labeled with the base, emitter and collector - it will show you the pin designations with a simple light indicator when they are connected correctly.

Answer 3

The only possible problem I can think of is the input impedance of photoisolator circuit is a good bit lower than the input impedance of the transistor circuit. That means the photoisolator will draw more current from the microcontroller than the transistor circuit. As long as your micro-controller output can handle about 5ma you won't have a problem. 5ma isn't much current. I also might consider putting a current limiting resistor between the coil and the power supply. Do you know how much current is required in the coil to activate the relay?