> >what's the purpose of the resistor from optocoupler to basis 
> of the two transistors?
> 
> To limit the current reaching the bases of the transistors.

Current doesn't reach, it flows. You use the transistors as
emitter-followers, so you don't need a base current limiting resistor.

Wouter van Ooijen

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Van Ooijen Technische Informatica: www.voti.nl
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