NPN switching transistor help *SOLVED*

Forum 2005-2010 (read only) Hardware Interfacing
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Hi all, I just got some NPN transistors for a project I'm working on and I think I'm probably using them wrong. Basically what I want is for the arduino to switch the transistor that is connected to 12v to power several LEDs. I've found countless tutorials and guides and I'm pretty sure I'm hooking it up right (but probably not).

Basically what's happening is if the base is LOW (or even if nothing is connected there) then the LED that I have connected is still about half lit. If I pull the base HIGH though it gets to full brightness. What am I doing wrong? If the base is LOW (or not connected to anything) then the LED should not be lit at all, correct?

The setup I have is similar to the photographed, handwritten schematic on this page: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1240103773

The only difference is my voltage and resistor values and a resistor between the arduino output and base. I'm new to transistors and I'm sure this is a noob mistake. Thanks in advance.

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The only difference is my voltage and resistor values and a resistor between the arduino output and base. I'm new to transistors and I'm sure this is a noob mistake.

Are you sure you have identified and wired the transistor properly? It's easy to get a bad reference/drawing as to which is the base, emitter and collector leads. If wired properly it could be a bad transistor and you should try another.

Lefty

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Ah, found the issue right after I posted. I misread the label on the back of the box, turns out I had mixed up the collector and emitter. My bad. Thanks a ton though :slight_smile:

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Ah, found the issue right after I posted.

But I still get credit for the SOLVED, right? ;D

Lefty