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Problems with MSP430 Launchpad 32.768 KHz Crystal!

Other Parts Discussed in Thread: MSP430G2553

Hello Everyone

 

I have been programming the MSP430G2553 for a month now, and when I was making a program including a clock, I noticed that the DCO inside the microcontroller was not precise enough to keep time with it. So I decided the solder on the 32.768 KHz crystal included with the package. I soldered on both of the forks and the body of the crystal down, I checked for any short-circuits and no-contacts and the multimeter confirmed that the crystal was soldered on properly. So after soldering, I fired up the launchpad and quickly wrote a program that blinked the green led with 1 Hz using the crystal as the clock source. It all seemed to work fine until I my finger approached the crystal from above "not touching". I noticed that the led stopped blinking whenever "I" was anywhere near the crystal within an inch I would say. I also noticed that when one finger was above the crystal, and the other finger was touching any pin other than GND, the crystal resumed working properly. Some of you might think the crystal isn't grounded well enough but the body of the crystal is well in contact with the area below.

 

So my question is, does this phenomenon happen to everyone or is the crystal I received with my launchpad garbage?

 

Thank you in advance!

  • I also noticed the same problem with my launchpad after soldering 32.768 crystal. I suppose it is a problem with contacts like open pin.

    Thanks,

    Dmitry

  • You (and your finger) are a really large capacitor.
    Coming near the crystal adds a parasitic capacitance to the crystal pins that might cause it to stop oscillating.

    It has nothing to do with grounding the case. It's the signal lines which pick up the capacitance.
    Also, on teh LaunchPad, the oscillator pins are also connected to the breakout connector (since the pins may be used as GPIO too). These lines act as an antenna - powered by your presence. IIRC, there is a jumper of some sort which allows to separate the breakout connector from the MSP when the crystal is attached.

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