[ale] My Raspberry π is here

[mike at trausch.us]

On 10/17/2012 11:06 AM, Michael H. Warfield wrote:
> On Wed, 2012-10-17 at 10:11 -0400, Derek Atkins wrote:
>> "mike at trausch.us" <mike at trausch.us> writes:
>>
>>> On 10/16/2012 04:05 PM, Scott Castaline wrote:
>>>> Finally got my π today and wifey wasn't here to grill me, so I'm a
>>>> very happy camper! Happy, happy, happy! Playtime now begins. Even the
>>>> FedEx guy has already been playing with one already.
>>>
>>> They are wonderful little things.
>>>
>>> I ordered 5 after last month's meeting so that we could play with them,
>>> and I am already looking at putting them to use to solve some
>>> long-standing problems that these are just absolutely perfect for solving.
> 
>> Okay, what long-standing problems are they absolutely perfect for solving?
> 
> I can come up with several just off the top of my head.
> 
> Easy:
> 
> *) A "little black box" with ssh keys, cron, and highly restricted
> access do manage remote server operations and interserver communications
> using key auth forwarding over ssh.
>
> *) A security storage module holding CA keys or PGP keys much like a
> smart card might due but higher capacity, higher performance, and lower
> cost.

I like both of these, particularly the latter one.  The Model A would be
better for this, I think, and (at least myself) I'd want to make a
custom case and remove all the I/O connectors and replace the dual-USB
with a single USB.  That'd make it really small.  :-)

> *) A remote serial console driver to monitor servers.  Sort of an add
> on, out board, server management module.

Would that not require additional hardware to convert from 5V to 3.3V?

> *) Server monitor.  Drop it on a remote network running nagios and
> health checks against your bigger servers.

Oooh!  Slave monitors capable of monitoring on the LAN when the World
Wide Pipe disappears, and can check in with a master monitoring server!

> *) Logging server.  Have it running rsyslogd and just saving syslog
> events off the local network to the SD card where it can't be tampered
> with by intruders who can't reach it.

YES!  I had that idea a couple weeks ago for a client office.  Swap the
devices out when they start getting full, and a great way to then be
able to control how things get archived.

> Because they're cheap, you can use lots of them as embedded controller
> devices for for small specialized tasks like these.
> 
> A much more difficult straw man idea I've been wrestling with:
> 
> (This one I believe Mike T will relate to immediate based on some of our
> recent discussions...)
>
> How about a DIY power line disturbance analyzer?  Take your AC power
> line signal (both phases) and divide it WAY down (say 1000:1) so it fits
> within range of an audio signal.  If you're not really concerned too
> much, some nice resisters will do along with some micro-fuses and
> transorbs.  If you are paranoid about playing with high voltage, some
> linear opto-isolators are even better, just more complicated.  Now feed
> those two signals to the stereo input of a USB audio adapter.  It's just
> a 60Hz signal, after all, with the two phases 180 degrees out of phase.
> Most ADC (analog to digital converter) daughter boards I'm seeing for
> the RP are two slow for what I want (15 samples per second for a 16 bit
> 8 channel board is NOT going to hack it).

Can we build it?  Can we build it?  Please?  :-)

> Now you can monitor and measure things like...
> 
> * Surges
> * Sags
> * Spikes
> * Dropouts
> * High frequency noise (notch for X10 and Insteon if desired)
> * Frequency
> * Voltage
> * THD (Third-order Harmonic Distortion)
> * Imbalances
> 
> Basically the things that a decent line disturbance analyzer does only
> without the $10,000 price tag.  Commercial units I've worked with will
> handle more phases and more inputs at higher voltages, are hipot (hi
> potential) tested and isolated for workplace safety, and are often
> calibrated and tracible back to NIST standards, which are not
> necessarily things we need (hipot isolation is desirable to protect the
> device but may not be necessary as a safety feature do to more limited
> voltages in the home).  That could be in the price range where you
> install it near your breaker panel and just leave it there and download
> data occasionally.

Can we install it?  Please?  :-D

> You can not measure things outside of the audio range of the device.
> Things like DC offsets and very low frequency that an ADC could measure
> but are generally not of serious concern.

It would be possible to make an add-on board with a microcontroller or
two that can then simply interface with the Rπ.  Something that would be
permanently installed like that could have the footprint on the wall
that is a bit bigger than the Rπ, perhaps the size of a normal
proprietary software box or so, meaning that if you really wanted to,
you could have the external board communicate signal levels to the π
using the GPIO pins, without such large division and keeping things in
more-or-less digital integer land.

I wonder, actually:  I have a multimeter that the screen is borked on
(was left in the car and crystals in the screen burst).  I wonder if the
circuitry in there, which handles up to 500V AC (as well as DC) would be
useful, though it's a black box to me.  That said, it's not a very
stable reading even on known-stable voltage sources like a brand-new DC
battery, so I don't know if it'd be very much quality.

> Add another audio input and some induction picks and you could add
> current monitoring.  Another audio input and you can have neutral to
> earth ground (common mode) monitoring.  Some nice beefy batteries can
> keep it going through some long power failures.  With enough on-board
> horsepower to do a decent FFT and you could store large amounts of
> signal data and events.

I don't understand much of how that'd work, but I do know that the thing
is supposed to be able to run on 4 AA batteries.  If that's the case,
then it should run on the (way too many) rechargeable cell phone
batteries that I have, when put together in a pack and with a suitable
charging circuit for them.  Alas, I have a lot of learning to do before
I could even think about attempting something like that.

> Yes, I've read the articles indicating that audio input to the RP has
> been less that sterling (sucks?  still?) and may be rather
> problematical.  That's something I really want to test and compare to a
> more general purpose device.

I've not interfaced with either the analog audio or video outputs, but
it strikes me as a very powerful device with the GPIOs that are
available, and almost all the applications I can think of that'd involve
extra hardware are things I think I'd want to be implemented in an
add-on board using the GPIO as an interface.  The only reason for that
is that I would want to protect the device from any external sources,
and use fused links for each of the GPIOs.  I've read that this board is
quite sensitive to out-of-spec-ness.

	--- Mike

-- 
A man who reasons deliberately, manages it better after studying Logic
than he could before, if he is sincere about it and has common sense.
                                   --- Carveth Read, “Logic”

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 726 bytes
Desc: OpenPGP digital signature
Url : http://mail.ale.org/pipermail/ale/attachments/20121017/66d08b93/attachment-0001.bin