Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
R2 is absolutely needed to limit the current through the base of Q2. The base-emitter junction of a bipolar transistor looks like a forward biased diode, thus the current is limited only by the external resistance if you apply a voltage above the forward bias voltage (about 0.6V) of the junction.
With R2 in the circuit, the 12V will not damage the PIC input, even if Q2 fails.
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.