nickey

That is holding current.
Actuating current, which is needed to move the mechanical parts, is much higher than holding current.
I don't think resistor in collector will work well, I don't think I have ever seen it used this way. Limiting relay's current is needed only when you need to preserve energy and it should be activated after the relay engages. For example one of the relay's contacts could be used as a feedback to the transistor to lower the current, but then the transistor will get hot.
 
That said, you do not need any resistors at all, the only component that is needed is a diode.

Just to back up what Rob is saying...
 
Find out how much current the relay requires to stay active. I think they call it Holding Current. That's how much current the NPN has to sink. Calculate the Collector resistor required. If Vcc = 12V and Ic = 10mA (this is the relay's holding current) then Rc = 12/0.01 or 1200 ohms.
 
I also agree with Rob, the biasing resistors shown are not required because you want to saturate the NPN into the conduction state. The only resistor that you should have is a Collector resistor to limit the current flowing through the NPN's collector.
 
I would also make sure to use the MSP430's internal pullup resistors on the I/O pin driving the NPN.
 
I hope this info is helpful.

It looks like R2 is there to make a voltage divider, to make sure VBE is low enough to keep the transistor in off state.
I bet you got that from some TTL design, because in TTL, low level can be as high as 0.8V, and that would be above transistor's cut-in voltage (typically 0.6V for bipolar transistors) making it conduct.
That said, you do not need R2.
 
You do not need R1 either, it is used to limit the current, but in this case it is not required.
MSP430's outputs are current limiting outputs. If you look at the spec sheet, in the "Typical Characteristics

Check out MC34063AP/MC33063AP from TI, they are available in DIP.

Take a look at this google image search for relay driver circuit.
 
There's some pretty good schematics that come up. You will see a theme amongst them all. An NPN driving a relay.
 
Hopefully, one of them will click with you.

Hello nickey,
for 12V to 3.3V checkout TI's, Maxim's, or LT's line of step-down converters.

Yes, there are debugging symbols inside the code. They don't take up much space.
 
You remove them by changing the build type to release instead of debug.
 
If you're using CCS then look in the top left window - "C/C++ Projects". See your Active Project? Hove your mouse over it and right click to bring up a menu.
 
See the sixth option down from the top "Active Build Configuration". Make it change to "2- Release".
 
Hit "Control B" to recompile and then you have your release build.
 
The release file will be located in a new directory called Release in your active project. The filename will end with the extension ".out".
 
If you convert this file to a ".hex" then you can use an external program to load it into the MSP.

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