Jump to content

Driving BJT with MSP430G2553

Recommended Posts

I'm trying to drive an NTE108 (BJT NPN) with an output pin on my MSP430G2553 and having trouble.  The output (P2.4) of the MSP is connected to the base of the BJT through a 330 resistor and controlled via software on the MSP.  I've attached a picture of the schematic (R1 is a recent addition).


Pin P2.4 works as expected when connected to the LaunchPad.  It can drive an LED and works when floating.  I cannot test it with the BJT (NTE108) because I only have one and it is soldered down.


I have moved the MSP over to a protoboard where it is supplied with a 3V regulator that can do 250mA.  Now the problems start...


P2.4 floats somewhere between 0.5V and 1.5V all the time.  It has not been configured in software for pullup/pulldown resistors.  It seems like there is some activity when the pin should change from the software, but the voltage variation is minimal.


If the base resistor R10 is disconnected from P2.4 and connected directly to Vcc (3V), it turns on the transistor as expected and the motor runs.  >> Maybe the MSP cannot supply the current to turn on the BJT...


If the base resistor R10 is disconnected from the MSP430, the pin floats near 1.0V regardless of software control (should be 3 or zero).  If R1 is disconnected, the same happens.>> Not a current supply problem.


I have checked that the chip is properly grounded and receiving adequate power.  I have moved the chip back to the LaunchPad and everything still works fine.


Any thoughts on why the pin is floating and cannot be controlled?  This is driving me crazy.  I only have problems on the protoboard so it's probably something to do with connections, but I've tried to check what I can.  Is there something I'm missing about moving the MSP430 from a LaunchPad to a protoboard?






Link to post
Share on other sites

Don't be so hard on yourself.  What is great about this board is that there are so many sets of helpful and experienced eyes that can see what we can't, especially when we are so close to the project that we can miss what in retrospect seems obvious. 


I have found this to be a great community.  Welcome!

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...