led O2 sensor

[Geoff Richards]

I have a 10 led o2 sensor that is commonly known to the list
I would like to be able to check the operation of each individual
led by applying the correct voltage to the signal wire.
My question is how do I make a SIMPLE variable voltage source
for this.
I have very LITTLE understanding of electronics so to any folks
kind enough to reply BEWARE it will need to be basic
I posted a similar question to a newsgroup and received an answer
that I really do not understand but would be able to send to anybody
willing to help out. 
Cheers
Geoff