LCD Backlight Proper Wiring

[DavyJones]

Melanie, I think you're going to have to start to charge tuition... I realize we've gone beyond a question regarding a general pic question I hope you don't mind the follow up. If I just asked you for the value of the base resistor I would not end up learning anything it would just show I am lazy and I am not.

Ok so let's say I just want to drive the backlight and go with a 2N2222 to accomplsih this. If I review the data sheet and the calculation I've looked up to calculate the needed base resistor I get: (Sorry if my symbols aren't exactly accurate. Hfe and Vbe from the datasheet)

Ib = Ic / Hfe = 120ma/100 = .120/100 = .0012
Rb = (Vdc - Vbe ) / Ib = (5 - .6 ) / .0012 = 4.4/.0012 = 3666 = 3.7k

If I add in a 30% extra 5 - .6 / .0012 * 1.3 = 4.4/.0015 = 2933 or approx 3k on the base resistor.

Did I get close?
Thanks again for your advice and assistance.
David

[Melanie]

Yes, you're good to fly solo on that one.

[DavyJones]

Yes, you're good to fly solo on that one.

I couldn't have done it without you! Thanks very much for getting me pointed in the right direction.

David