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Raspberry Pi Flakiness


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#1 brett

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Posted 16 December 2014 - 05:52 PM

I've got a Virtual Wiring system running on a Raspberry Pi B.  After a period of days, the system halts (can't do anything and only the Pi's red light is on).  Any ideas?  Could it be that Virtual Wiring is the problem?


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#2 Felix

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Posted 16 December 2014 - 06:44 PM

It's not likely that Virtual Wiring is the problem.  VW is just an application, so it would be hard for it to crash your system.  If you are running it as root (not necessary or advisable), and you've written some of your own Ruby code, it's possible you could crash your system.  But even then, you'd probably have to work at.  Ruby is generally pretty safe, unless your are running system commands (commands in double back ticks).

 

From the sound of things, you've got a power problem.  Raspberry Pis are great little machines, but their achilles heel is they rely on third party power supplies and cables.  The quality of 3rd party supplies is all over the map.  In addition, the USB cables from the supplies to the Pi are typically too small.  We've looked at a lot of power cables and many of them are 28 gauge wire.  A 6 foot long 28 gauge cable will drop near 0.4V with one Amp running over it.  If your power supply is 5V, you'll be ~0.1V under the minimum power supply voltage of the Pi with a 28 gauge, 6 foot USB cable.  Often Pis will seem to work if they run under voltage, but they get "flaky".

 

We've got a solution which has worked well for us.  We buy Apple iPad/iPhone USB supplies (little wall warts).  They are rated for around 12W of output at 5.2V.  We also buy 20 gauge USB cables from Amazon (search for "20AWG micro usb cable").  Keep the length of the cables as short as reasonable, as longer cables will drop more voltage.  Most of our cables are 6ft/2m.  The beefier cables and the additional 0.2V of the Apple supplies delivers Pi power which is well within spec.  The Apple supplies are a little expensive, but we've avoided the hassles of flakiness.

 

If you are buying a new Pi, we recommend the B+.  In addition to more USB ports, the B+ has better power circuitry and drops less voltage on the card.



#3 brett

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Posted 16 December 2014 - 06:52 PM

I checked my USB cable, and it's 28 gauge.  Gotta be the problem.  I'm ordering a new one.






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