Low-power device recommendation

On Mon, 11 Oct 2004 10:21:42 +0300, "Peter" <peter@greatnowhere.com>
wrote:

> Hi all,
>I'm new to embedded scene, and totally lost here. I'm looking to design a
>totally stand-alone weather station and need to select a device for this.
>Requirements are:
>
>* low power consumption, ability to feed off single voltage (~12V solar
>power)

At what latitude are you ? That will determine the height of the sun
in the winter and thus the number of hours of daylight and the
atmospheric losses (airmass). What are the weather conditions in the
winter ? If there is a lot of clouds in the winter months, the solar
cell output will drop even further. Thus you may need backup power for
weeks or even a month. Thus, the average power consumption needs to be
extremely low.
 
>* 2x RS232 ports
>* Ethernet (10Mbit will be fine)

If this is a stand alone device, what do you need the Ethernet for ?
Such high speed devices consume a lot of power. 

>
>* solid-state disk (regular HDDs will consume too much power, and probably
>won't work outdoors)
>* ability to run "conventional" Linux that I can manage using shell access.
>I'll also need to run Python and Perl on the box. 

>Internet connectivity will
>be either IPv4 (DHCP, ethernet), or PPP via serial. 

So this is not a stand alone device after all ?

Why not run the power over ethernet or take it from the RS-232
handshake lines (assuming your system runs on a few milliamps).
 
>Having a small MySQL
>server would be nice but I can probably live without it - it's probably
>going to require too much disk space anyway
>* CPU-wise requirements are very low - basically it needs to poll serial
>port every second, and send off aggregated data every minute or so

If those are the requirements, then the system could be powered off
for 99 % of the time to save power. Thus, you need a system which can
go into deep hibernation and wake up with an external interrupt, such
as a CMOS clock once a second or you need an OS that boots in much
less than 100 ms if you do a restart every second.

>* extremely stable - will need to run unattended for months
>* weather-proof(able)

This depends on your environment requirement.

If plenty of power would be available, it would be quite simple to
keep the component and cabinet indoor temperature 5-10 degrees above
the ambient temperature (even when a warm wet wind rapidly increases
the temperature). This will prevent condensation on the components and
you can use a box with holes in the bottom to ventilate the box and
get rid of humid air when the temperature drops. With sufficient power
you can even keep the indoor temperature above 0 C (since some
components are not specified for subzero temperatures).

>* cheap! This is my personal project!
>
>Any recommendations appreciated!

You must either do something about your power supply or rethink the
division of labour in the system, e.g. transmit the raw measurements
directly from a system with extremely low power consumption and do any
hard processing in a system with more resources.

Paul
 

Peter wrote:
> 
> 
> Why? From what I can gather TS-7200 consumes about 1.7W tops - easily doable
> with solar power & batteries. I'm not too technical so 'fraid programming a
> microcontroller will be too complicated. Even if I managed it (read: ported
> weather station polling software to a microcontroller), consider this: it's
> going to be a standalone unit, and connected to servers only via Internet
> (Ethernet or serial PPP + GPRS modem). It will need to send off data
> periodically to the server. Can a microcontroller handle this?

  For an Ethernet/Web uC, look at

http://www.maxim-ic.com/products/microcontrollers/micro_ethernet.cfm
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3743/ln/en
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3744

> > (Ethernet or serial PPP + GPRS modem). It will need to send off data
> > periodically to the server. Can a microcontroller handle this?
>
>   For an Ethernet/Web uC, look at
>
> http://www.maxim-ic.com/products/microcontrollers/micro_ethernet.cfm
> http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3743/ln/en

OK, that will take care of Internet connectivity via Ethernet. What about
PPP dialup? Any MCs capable of doing this?

Thanks!
Peter

> >   For an Ethernet/Web uC, look at
> >
> > http://www.maxim-ic.com/products/microcontrollers/micro_ethernet.cfm
> > http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3743/ln/en
>
> OK, that will take care of Internet connectivity via Ethernet. What about
> PPP dialup? Any MCs capable of doing this?

Never mind, I found the answer... TINIm400
(http://www.ibutton.com/TINI/index.html) fits the bill perfectly: dual
serial ports, ethernet, 1-wire interface (which I need for weather station
anyway), Java runtime, PPP support, cheap (70$ or so + development interface
100-150$). My only reservation about this board is that it plugs into SIMM
connector which means I'll have to connect all physical connectors (serial
etc) to it somehow. Also, it takes regulated 5V while all solar
panels/batteries I've been able to find are 12V.

"Peter" <peter@greatnowhere.com> wrote in message
news:2t1nnbF1q4b45U1@uni-berlin.de...
> > >   For an Ethernet/Web uC, look at
> > >
> > > http://www.maxim-ic.com/products/microcontrollers/micro_ethernet.cfm
> > > http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3743/ln/en
> >
> > OK, that will take care of Internet connectivity via Ethernet. What
about
> > PPP dialup? Any MCs capable of doing this?
>
> Never mind, I found the answer... TINIm400
> (http://www.ibutton.com/TINI/index.html) fits the bill perfectly: dual
> serial ports, ethernet, 1-wire interface (which I need for weather station
> anyway), Java runtime, PPP support, cheap (70$ or so + development
interface
> 100-150$). My only reservation about this board is that it plugs into SIMM
> connector which means I'll have to connect all physical connectors (serial
> etc) to it somehow. Also, it takes regulated 5V while all solar
> panels/batteries I've been able to find are 12V.
>
>

You will need to regulate the solar cell output. If you want the thing to
work at night you will also need battery power. Look at a shunt regulator
for the charging the battery and a DC/DC converter to go down from 12V to
5V.

Peter


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"moocowmoo" <meltyb@hotmail.com> wrote in message
news:ckgcv1$v1$1$8302bc10@news.demon.co.uk...
>
> "Peter" <peter@greatnowhere.com> wrote in message
> news:2t1nnbF1q4b45U1@uni-berlin.de...
> > > >   For an Ethernet/Web uC, look at
> > > >
> > > > http://www.maxim-ic.com/products/microcontrollers/micro_ethernet.cfm
> > > > http://www.maxim-ic.com/quick_view2.cfm/qv_pk/3743/ln/en
> > >
> > > OK, that will take care of Internet connectivity via Ethernet. What
> about
> > > PPP dialup? Any MCs capable of doing this?
> >
> > Never mind, I found the answer... TINIm400
> > (http://www.ibutton.com/TINI/index.html) fits the bill perfectly: dual
> > serial ports, ethernet, 1-wire interface (which I need for weather
station
> > anyway), Java runtime, PPP support, cheap (70$ or so + development
> interface
> > 100-150$). My only reservation about this board is that it plugs into
SIMM
> > connector which means I'll have to connect all physical connectors
(serial
> > etc) to it somehow. Also, it takes regulated 5V while all solar
> > panels/batteries I've been able to find are 12V.
> >
> >
>
> You will need to regulate the solar cell output. If you want the thing to
> work at night you will also need battery power. Look at a shunt regulator
> for the charging the battery and a DC/DC converter to go down from 12V to
> 5V.
>
Be sure to put in a switchmode converter with MPPT to optimize the power
from the panel. A shunt converter set at a fixed voltage will be very
in-efficiant

/Klaus

Peter wrote:
>>>Definitely cheap, $59.95.
>>
>><*Spits coffee all over keyboard*>
>>
>>(In comp.os.linux.embedded, $60.00 is cheap, but
>>in comp.arch.embedded, $1.00 to $0.10 is cheap.)
> 
> 
> Geez man, TS 7200 is 160$... definitely more expensive than Linksys unit!
> 
> 
The TS-7200 will have more capabilities and expandability.
The Linksys will be more fun for hacking.
Its really up to you.
T.

 >Also, it takes regulated 5V while all solar
> panels/batteries I've been able to find are 12V.
> 
> 

If you don't know about switching voltage regulators, please stop 
thinking about building solar driven intelligent devices.

-Michael

> >Also, it takes regulated 5V while all solar
> > panels/batteries I've been able to find are 12V.
> >
> >
>
> If you don't know about switching voltage regulators, please stop
> thinking about building solar driven intelligent devices.

Hey, we all gotta start somewhere! ;) Will have to learn this stuph about
voltage regulators I guess... this is a learning experience for me.

Peter

"Peter" <peter@greatnowhere.com> wrote :

> consider this: it's going to be a
> standalone unit, and connected to servers only via Internet 
> (Ethernet or serial PPP + GPRS modem). It will need to send off
> data periodically to the server. Can a microcontroller handle
> this? 

thats exactly what microcontrolers are for !

Pozdrawiam.
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