> Err... on a TO-92 case, the base is the middle one, right? 
> How do you know
> which is the emitter and which is the collector?

>> BTW, you have got the transistor wired up right ?

Varies with type.
All are variants of bce and ebc plus reversals.

Look in datasheet for the type you are using.
Digikey are a quick way to access data sheets for many 
parts.

There are complexities but few matter here.

Brief:
Transistor supported collector current is base current x 
current gain.
Current gain is call Beta.
Base current ~~= (Vdrive-0.6)/Rbase

or Rbase <= (Vdrive-0.6)/ base current

~~= (Vdrive-0.6)/ (relay_current/Beta)

For say 100 mA relay current and conservative Beta = 50 or 
more (OK for many small transistors)

Rbase <=~~~ (5-0.6)/(100mA/50) = 2200R

So use a 1K base drive AND connect the transistor correctly 
and it should work.

Many/most multimeters have a beta tester included. Socket 
labelled cbec or whatever.

- Establish probable connection pattern.
- Test with meter beta tester.

Beta should be say > 100 and ideally 200+ at current used by 
meter


        Russell McMahon


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