If you only need to send data 400 feet you could
look to 433MHz radio modules. (They are similar to Garage door remotes,
but designed for serial data).
I'm thinking a microcontroller at each end of the
400 feet. One to the device and the other into the serial or ethernet
port.
They are really cheap - starting at US$5. I would
caution though, the slighly more expensive ones do seem to provide people with
a better experience.
Lightning cannot strike the wireless part of a
wireless link :)
In the US, www.sparkfun.com also have some easy to use
wireless modules. They claim you can just feed serial in one and data comes
out the other. I've never used them so I can't vouch for that
personally.
If for some reason you need to convert the
received data to analogue (but I don't think you will), you can just use an
DAC (digital-to-analogue convertor). The speed at which you need to convert
the digital signal will be a big factor in the price of such a chip. Some
basic ones are here: http://www.futurlec.com/ICDAC.shtml
As for range on SAW wireless modules, some claim
over a kilometre. To get this though would require a proper antenna I'd
imagine. For 400 feet you could probably get away with just a nice small
antenna. This really isn't my area though :)
Ethernet with microcontrollers has always been a
bit expensive for my tastes :)
But see the "Ethernut board" at avrfreaks. There
are also quite a few around. As for 400 feet from a microcontrolled board I
don't know. Plus the added problem of communicating with a router and all the
protocols that need to be implemented might be beyond a simple
microcontroller.
This is why my designs usually have two micros at
each end of the wireless link with one talking to a PC via a serial port
- no TCP/IP overhead :)
----- Original Message -----
Sent: Friday, October 22, 2004 4:09
AM
Subject: RE: [AVR-Chat] Re: Remote site
questions
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