[ale] My Raspberry π is here

Wed Oct 17 11:06:37 EDT 2012

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.

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

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

*) 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.

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).

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.

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.

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.

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.

> > 	--- Mike

> -derek

So...  Those are just a few ideas.

Anyone else?

Regards,
Mike

> -- 
>        Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
>        Member, MIT Student Information Processing Board  (SIPB)
>        URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
>        warlord at MIT.EDU                        PGP key available
> 
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-- 
Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw at WittsEnd.com
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