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Electronics => Beginners => Topic started by: wblackledg on February 18, 2015, 08:09:08 pm

Title: noob circuit question. hardware for software dummies help!
Post by: wblackledg on February 18, 2015, 08:09:08 pm
I'm a software guy, not a hardware guy so  I think in terms of setting up a program.

I have this book (see link). Amazon allows you to view even / odd pages so lucky for me my question resides on On page 86.

http://www.amazon.com/Make-Electronics-Discovery-Charles-Platt/dp/0596153740/ref=sr_1_1?ie=UTF8&qid=1424186364&sr=8-1&keywords=make+electronics#reader_0596153740 (http://www.amazon.com/Make-Electronics-Discovery-Charles-Platt/dp/0596153740/ref=sr_1_1?ie=UTF8&qid=1424186364&sr=8-1&keywords=make+electronics#reader_0596153740)

Question:

Looking at the circuit on page 86, they place the resistor (R6) behind the transistor in the flow.  As a programmer I would think it would be in front of the transistor because you are trying to limit the current. However is this resistor like a stopper on a sink, in that the juice is flowing out of the faucet, and by putting the resistor behind the transistor you are cutting the flow off as it drains out?  Hope that makes sense. Just wondering if I understand why the resistor is placed where it is.

hope that makes sense?

thanks in advance.
Title: Re: noob circuit question. hardware for software dummies help!
Post by: Christopher on February 18, 2015, 08:25:18 pm
The base-emitter junction is like a diode. You have to limit the voltage across it otherwise it will just allow too much current through it, damaging the device.

The same reason why you put a dropper resistor in series with an LED
Title: Re: noob circuit question. hardware for software dummies help!
Post by: wblackledg on February 18, 2015, 08:35:13 pm
Quote from: Christopher on February 18, 2015, 08:25:18 pm
The base-emitter junction is like a diode. You have to limit the voltage across it otherwise it will just allow too much current through it, damaging the device.

The same reason why you put a dropper resistor in series with an LED

ok thanks for responding.  However I'm still not sure why the Resistor goes behind transistor and not in front of it?
Title: Re: noob circuit question. hardware for software dummies help!
Post by: wblackledg on February 19, 2015, 03:51:29 am
I think I figured it out after looking at it again.

thanks.
Title: Re: noob circuit question. hardware for software dummies help!
Post by: Seekonk on February 19, 2015, 04:08:47 am
 "behind transistor and not in front of it? "

For the life of me I can't figure out what that means.
Title: Re: noob circuit question. hardware for software dummies help!
Post by: wblackledg on February 19, 2015, 04:13:13 am
Quote from: Seekonk on February 19, 2015, 04:08:47 am
"behind transistor and not in front of it? "

For the life of me I can't figure out what that means.

I meant that flow of electricity.   The resistor connection was after the transistor in the circuit.  It didn't make sense, but  believe it does now.
thanks.