AVR-Chat

Thanks to all for you comments on my remote site question.  Thanks to Dingo in
particular for providing part numbers.  See more comments interspersed below:


> From: Dave Mucha
> 
> ....
> I use the 12.5mm solder leg verson for my RTC's, or the 22mm 
> for larger projects like data loggers that are only powered 
> briefly and are unplugged 99% of the time.
> 
> For the sunny climate, a solar charger will be of great use 
> to re- charge your battery packs.
> 
> also, read the data sheet for the RTC.  Some have the ability 
> to trickle charge the back-up battery.

The site has 110VAC power 99% of the time so I think a button cell would easily
cary it through the power outage cycles.


> From: Bernd Felsche
> 
> ....
> Independent RTC... mainly because of it makes the programming 
> much easier ans well as ...

The DS1307 that Dingo recommended looks good to me.  Now I have another thing to
learn, SPI, :-)

> ....
> Independent RTC with its own battery. Monitor battery voltage 
> with the AVR when the controller is active. The controller 
> could go into a low-power mode and be woken up once a second 
> (or so) by the RTC driving an interupt.

The DS1307 auto switches to a button cell and the AVR has brown-out detection so
I think I'm covered there.

> ....
> Transorbs on power and "local" wiring. Optical isolation on 
> signal inputs with long wires.

While searching the net for info on Transorbs I found this on Lightning
protection that may be of interest to others:
http://www.telebyteusa.com/catalog/refinfo/appnote1.htm

I searched Digikey (and International Rectifier) for "Transorbs" but didn't come
up with anything.  Having seen the above web page I searched for "avalanche
diode" and came up with 69 items on Digikey ...

Am I searching for the wrong thing?

Would I be looking for Schottky or "Standard Recovery" avalanche diodes.  Also,
I saw none with voltage ratings below 100V.  For the analog data lines I assume
I'd be looking for something in the 10v range.

Since I'm protecting an analog signal line here I assume optos are inappropriate
(at least I've only seen ones suitable for digital, as opposed to analog,
links).  I assume that the Transorb does not effect the signal line until the
voltage exceeds it's rating?  I also assume they conduct in the forward
direction like a normal diode if the surge takes the data line in the reverse
direction (i.e.: forward polarity with respect to the Transorb)?

> ....
> SMTP is amazingly simple, but the underlying TCP/IP stack is 
> quite a lot of baggage. If you have a dialer, then why not 
> simply call a pre-determined number, have that answer and log 
> the status? Thsi is how many "monitored" alarm systems 
> operate. 

If I had a predetermined phone number it would have to be dedicated to this
function with a system to answer it.  Seems like overkill when the Internet is
everywhere.

I just realized that I do have high-speed Internet available but it's about 400
feet from the device and there is a Telco grade twisted-pair cable between the
site and the location of the cable modem.  Does anyone know of a 10-BaseT line
driver/converter that can drive 10mbit over 400 feet of twisted pair?  If so I
could use one of the 10-BaseT Internet devices.

----------------------------------------------------

Further thoughts on the clock:  Since the 110VAC power is up 90% of the time
and, as I understand it, powerline frequency is very accurate over long periods
(e.g.: 24 hours) but not necessarily over short periods.  Are there any RTCs
that have a 'reference' input that can be derived from the power line to keep it
accurate when the 110VAC power is present?

Communications:  No one has a URL for libraries that support SMTP/POP3/TCP/IP
functions over Async?  (I haven't searched AVR freaks yet but it's on my list).

Thanks again to all, sorry for the long message :-)

Cheers,

Chuck Hackett
"Good judgment comes from experience, experience comes from bad judgment"
7.5" gauge Union Pacific Northern (4-8-4) 844
http://www.whitetrout.net/Chuck