Date: Thu, 22 May 2014 19:34:10 +0200 From: Bernd Walter <ticso@cicely7.cicely.de> To: Luiz Otavio O Souza <lists.br@gmail.com> Cc: "freebsd-arm@freebsd.org" <freebsd-arm@freebsd.org>, Ian Lepore <ian@freebsd.org> Subject: Re: BBB MMC / SD detection instability with U-Boot 2014.04 (CPU 1GHz) Message-ID: <20140522173410.GB92212@cicely7.cicely.de> In-Reply-To: <20140522170414.GA92212@cicely7.cicely.de> References: <CADH-AwGb36EUknNofdch1Q4Pn8GAN%2BEp9SdiJ_f7Q2v9e4kW1g@mail.gmail.com> <20140522.204656.144162099.toshi@ruby.ocn.ne.jp> <1400765234.1152.224.camel@revolution.hippie.lan> <20140522.231553.186386229.toshi@ruby.ocn.ne.jp> <CAB=2f8xyzLQpTQgwc8EHh-_A-0HV_H3w_7uW_RAYXM8X_Q02MA@mail.gmail.com> <20140522170414.GA92212@cicely7.cicely.de>
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On Thu, May 22, 2014 at 07:04:14PM +0200, Bernd Walter wrote: > On Thu, May 22, 2014 at 11:34:50AM -0300, Luiz Otavio O Souza wrote: > > Just picking one email to reply... > > > > This is probably unrelated, but i can consistently corrupt my SD Card > > data if i connect (and use) a very small R/C servo (the 9g ones, used > > on foam planes) to the 3.3v on the expansion headers. > > R/C servos usually are extremly harsh on power sources. > I know this because decades ago I'd build LED based akku charge displays > for R/C helicopters and I needed a lot of input filtering to not sweep > over the full display range when servos had been active. > > > I'm not sure if it is because of noise or the power consumption, but > > looks like the BBB is really picky about the power conditions here. > > It is the noise on the power consumption. > I don't know how good the 3.3V rail is stabilized, but I wouldn't > be surrised the the servo would produce a noise level of way more than > 3.3V, so your rail even can be negative or more than doubled. > This can even damage components as they are not designed to handle > such voltages. > > > Connecting the servo to the VDD_5V on the same header makes the problem go away. > > The 5V rail is likely not directly used in any digital circuitry > beside the volatage regulators input and their output are > influenced. uninfluenced... > The volatage regultaors however are also designed for small input voltage Doing low level stuff makes one type volatile too often. Amazing how often I misstype voltage now. Stupid fingers... > ranges and can be damaged by invalid input voltages on the 5V rail. > An inductive load can be a power sink or a power source! > Effectively you are connecting something to the 3.3V or 5V rail, > which sometimes act as a high voltage battery. > > > So be careful about what you connect on your boards :) > > Absolutely. -- B.Walter <bernd@bwct.de> http://www.bwct.de Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.
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