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MintyBoost, Arduino and XBee - Some Findings
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MintyBoost, Arduino and XBee - Some Findings

by rocketboy001 on Sat Dec 28, 2013 2:40 am

I have been working on a project that used the MintyBoost along with the Adafruit solar charger to power an Arduino Pro Mini, an XBee and some LEDs. The project final project will live outside.

When I begin testing the project outdoors we were getting some pretty low temps, well below freezing and during the testing I was getting some odd behavior. I thought the odd behavior was related to the Arduino getting too cold sine the issues all seemed to be timing related and so I though that maybe the Arduino's clock was getting too cold. But after checking the datasheets for most of the components I found that they were all rated to well below the temps they were in. One thing - I had not started with an IP rated enclosure, since the electronics enclosure was mounted inside another box I figured just a regular run-of-the-mill plastic enclosure would do. Eventually, out of desperation, I moved everything into an IP65 rated enclosure.

Things seemed to improve a bit after I moved to the IP65 enclosure, it was a thicker plastic and I also changed the mounting of the enclosure so that it was not sitting up against the wall of the metal box it was in. But I was still getting some inconsistent behavior, at this point it seemed to be isolated to the XBee. The Arduino was programed to send out a character via serial 10 times, while I was seeing the character being transmitted I was not seeing it the ten times I should - 2, 3, 4, maybe 10 if I was lucky. I knew it was related to the cold temps because I could induce the behavior if I placed the components in the fridge (sealed in the case of course). 30 min in the fridge was enough to cause the issue to show. I eliminated the battery as a possible cause by removing it during one of the fridge tests. As long as the components were cold, I would see issue but once they warmed up things worked perfectly.

Outside temps started to warm up, but even in the low to mid 40s I was still seeing inconsistent behavior. Bring everything in and let it warm up and bam! It worked.

Fast forward a bit and I happened to notice during one of my fridge tests that the MintyBoost was whining when it was cold. I was not concerned with the whining because I know the coil can do that under load. It does seem odd since I'm not even approaching the limit of the MintyBoost but it made me think. Despite my measurements showing that the MintyBoost output stayed within spec when it was cold, maybe the output was just noisy enough that it was causing issues. Or maybe the MintyBoost being in close proximity to the XBee, when cold and under load caused interference that resulted in the inconsistent transmissions.

So, I placed the biggest cap I had on hand (4400uF) inline with the MintyBoost output. Lo behold the whining stopped. I ran a fridge test for the same 30min I'd used before and everything worked perfectly. I've had the project outside for 3 days now and despite temps in the 30s everything seems to be working swimingly.

I guess the upshot is that at least in cold temps the MintyBoost may produce unstable output. Placing a filter cap on the output seems to solve the issue.

tl;dr: if you are using the MintyBoost to power, rather than charge, a device add a filter cap on the output to prevent issues.

rocketboy001
 
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Joined: Thu Feb 12, 2009 3:01 am

Re: MintyBoost, Arduino and XBee - Some Findings

by adafruit_support_bill on Sat Dec 28, 2013 9:27 am

Interesting. Thanks for posting your findings.

adafruit_support_bill
 
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Joined: Sat Feb 07, 2009 10:11 am

Please be positive and constructive with your questions and comments.