Sunday, August 26, 2012
Raspberry PI - Power Supply and USB Problems
Read an article on Slashdot that says the Raspberry Pi has some "problems".
The actual article seems a bit alarmist, to summarize the key information there and in the referenced articles:
1) The rPI gets flakey if you don't use a powerful enough power supply
2) The USB peripherals apparently can't deliver the 500–900 mA that the USB spec calls for (Ref 1)
The interesting thing is that I have observed both of these problems, but quickly figured them out and have had no issues since.
1) I tried powering the rPI from a couple of USB hubs with external power supplies that both said "1 AMP". On the first one, it would get part way through the boot process and reboot, getting stuck in a boot loop. On the second one, it would not even start the boot process. I fixed the issue by running the PI from a heavy duty 4 Amp analog open frame power supply that I scrounged from some piece of junked gear (have to write a blog posting on the joys of scrounging junk :-)
2) I first tried a really old USB keyboard (a real "IBM" one - remember when they made PCs :-) and it acted flakey, repeating and missing characters. I swapped it out for a newer one, works fine. My conclusion is that the newer one drew less current and worked fine, although I did not measure it.
So to me all the alarmist postings are a bit of an overreaction, moral of the story is to use a GOOD beefy power supply that can deliver the 1 AMP the rPI needs (Ref 2) PLUS the combined current that the 2 USB peripherals need. Better still, use an external self powered hub for the USB peripherals.
Eric Pierce VA3EP - See the Disclaimer in the Introduction
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