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Shorted out msp430

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I am working on a circuit that drives some 7-seg displays and a relay based on a sensor reading. I have the circuit built and I am powering it with an old variable supply I built in a class. The supply is at 5V when its not loaded and when I connect it, it drops down to about 2V. So I adjusted it up to 5V. My relay clicked on but nothing works on my 7-seg displays. Now I realized that I somehow shorted the msp430s VCC and GND pins together and the same thing for the launchpad which gets really hot when its connect to the usb now. I cant figure out what I did that caused this and I am looking for some help. Ive attached a basic schematic of my circuit plus the relay driver that I am using. Thanks!



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The first rule of troubleshooting is "Thou shalt divide and conquer".


In other words, take the circuit apart methodically and retest for the failure condition. Change one thing at a time. Repeat until the failure condition disappears. The last change you made contains the failure.


What is the SR1 device?

What voltage does it operate with?

Can you provide a bill of materials so we know what we're looking at?


If you have to increase the voltage on the power supply then there is something wrong in your circuit. Resist the temptation to increase the voltage setting on the power supply. You will definitely let out the magic smoke on the parts.


What component gets hot? Use your finger to find out. Or an infrared thermometer. Or use some freezy spray and see which part melts the frost first.



Disconnect power. Grab your digital volt meter. Measure resistance between Vcc and GND on the MSP430. What is it? 

Pull the MSP430 out of the Launchpad. Does the resistance between Vcc and GND change?


How are you connecting JP2 to the other circuit diagram?


Your launchpad is powered by the PC via USB. Your circuit is powered by the bench power supply. Without isolation, this setup will cause problems.


Test the relay circuit all by itself. Disconnect it from the MSP430 circuit, apply 5V to JP2, short JP2 & JP3 together. Does the relay activate?


Test the MSP430 circuit all by itself. Power it via the Launchpad's USB, does the 7-seg display do its thing?

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After looking at it, I think it could be a ULN2003 or a 74HC595 but they have only 16 pins. This mystery unit has 20 pins. So, back to basics. 


I can see that the LED has a 5V supply voltage. That is the first red flag.

The mystery chip is connected to the MSP430. That is the second red flag.


I theorize that @@jgelderloos is commanding the MSP430 to ground out certain pins on the MSP430 to drive the mystery device. My intuition says that will activate the MSP430's GPIO protection diodes.


In the absence of more information from @@jgelderloos, I choose to believe that this circuit is not working because of the supply voltage mismatch.

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That looks like a strong possibility. Yeah, I think we have a winner! Good work Frida!


Vcc = [4.5..5.5]V

Vih = (0.85)(Vcc)

ViL = (0.15)(Vcc)


The MSP430 will not be able to drive any of those pins high enough without external assistance.


Conclusion: POOF!




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