relay with transistor as switch-what am i doing wrong?

Other Hardware Motors, Mechanics, Power and CNC
1

Hello,

I'm trying to make a transistor-switched relay operate as shown in this diagram here: Arduino Playground - HomePage

I've set up everything according to the diagram. However, the behavior is not what I expected:

When relay source voltage (6v external power supply) is applied, relay closes contacts, even without power applied to the arduino.
When arduino pin goes "HIGH", the contacts on the relay open, when they go "LOW" (as when it's off) the contacts close.

additional info: Transistor model: 27p06, which I understand to be NPN type.

I know this is something boneheaded that I've overlooked or misunderstood. I thought I properly understood how this circuit works, but I clearly do not. Can someone provide some guidance? Thanks in advance,
-shane

2

http://www.fairchildsemi.com/ds/FQ/FQP27P06.pdf

This is a datasheet for27P06, looks like a p-channel.

3

Wow, i feel dumb. I think ive misunderstood the difference between p and n channel. After doing a little more research, i think i get it now. Thanks for the help!

-shane

4

Don't sweat it, it happens to the best of us :grin: