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MSP430G2955 wireless temperature sensor


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Yeah I know everyone has done one of these but it's a good learning project. Basically a 1x1" board with a 2955, button, LED, thermistor and a header for an NRF2401 board. I also did a similar board for the STM32L series (but not back yet from OSHPark) and plan to compare both to see which performs better overall.

 

End goal is to end up having a number of these sensors throughout my house, periodically logging temperature to a central USB connected device. Preferably with 1+ year battery life on 1-2 AAAs.
 

Overall the board came out pretty nicely, only changes I'd make would be.

  1. A bit more spacing between the 10uF and 0.1uF capacitors.
  2. Reverse the SBW connector (makes it easier to connect up to the FET)
  3. Switch the serial header to either have only T and R, or T, R, + and -
  4. Maybe put all the components on top, though moving the caps to the bottom saved a ton of space
  5. Smaller or no RTC crystal

Nothing really bad and for a noob I think it came out pretty well.

 

Only issue I have is that putting a 2.2nF capacitor between GND and RESET caused it to not always properly restart. Removing the capacitor fixed the problem and I'll probably try replacing it with a 10nF to see if it still causes a problem. Not really sure what the proper value is, there's some TI docs that state no more than 2.2nF, there's at least one schematic for this chip that shows a 10nF.

 

Feel free to comment, critique, ask questions, etc...

 

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Reminds me, I need to calibrate my G2452-based wireless temp bugs and deploy them.

 

I would not use anything larger than 2.2nF on the reset pin if you ever expect to program it; prefer much less than that, I often use 470pF since I have 'em in my bin.  I'd switch to 1nF if I had them.  Something higher than nothing just to help stabilize it, but in reality many have no problems even without a cap there.

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Nothing so far seems to work pretty well, I picked 10nF because that's listed on the MSP-TS430DA38 board (http://www.ti.com/lit/ug/slau278n/slau278n.pdf

 page 57), but I see now that it has a DNP on it, so no idea why they even put it on there. Will try < 1nF to see what happens.

 

BTW thanks for the help starting out with DIPTrace!

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In case anyone is interested (though arguably off topic) this is the STM32L version of the "same" board that I'm going to use to compare to the MSP430 version. Crappy soldering job is somewhat due to having a short somewhere and I had to desolder everything to find it (ended up being on the STM32L, ugh).

 

This one is a bit more complex than the MSP430 version since I added a UEXT like port and used the 64 pin version instead of 48 so I could screw around with the same design and use some of their other chips.

 

Lots of stupid little mistakes on this one but only two major issues. 

  1. The RTC crystal requires caps on the STM32 series and this one doesn't have any (doh!).
  2. I didn't put in any jumpers to allow switching between boot modes (flash vs SRAM boot), you wouldn't think this is a big issue if you aren't familiar with these chips but without this option its very easy to get the chip in a state where it's "bricked".

Because of issue 2 I won't be able to play around with external clock, which rules out USB for this version of the board. But hey at least it's good enough to blink and give me some more experience with this family while I wait for yet another couple weeks till a new version gets delivered.

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