AVR-Chat

Not knowing what you meen by the controller but I it seems to me that 
the AVR/LCD would also be part of your controller.

As for the devices that feed you this info. The Door-Open, Ignition-
On, Smoke-Alarms and Motion-Detectors are binary and each couild be 
connected to it own pin on the AVR. The Oil-Pressure-Low in itself is 
binary but what ever detects the actual pressure is analog in and 
binary out.

For most applications the binary inputs could be hundreds of feet 
away.

For a temperature sensors with 1-wire devices a single AVR pin can 
handle 8 devices. A thermo-couple could be used without concern of 
the distance in a car. Actually the distance you will be running in a 
car probably noise and not the length of the cable will be a problem. 
The AVR has a very high input impedance so almost no current will be 
flowing. With zero current across any resistance and zero voltage is 
dropped. 
Voltage = Current x Resistance
V = 0 x 100 (100 ohms here is way too big still the result is zero)
Oh, you might have a microamp or so draw but still that would give 
you a drop of only about 1/1000 volt.

Now, if noise is picked up your readings could be all over the map. 
To cut down on noise you might try 2 wires with a shield. The shield 
only touches GND in the car at the AVR box. Then again noise may not 
be a problem. You need to do a little tril and error research here.

Mike


--- In AVR-Chat@yahoogroups.com, James Washer <washer@t...> wrote:
> I'm a newbie at playing with HW.. I've been a software guy forever. 
Sorry for leaving out details.
> 
> I've got a couple of different situations. 
> 
> 1) I want to have a remote AVR with an LCD that shows system 
status. Nothing major, but with any of say 20 inputs( think 
automobile, door open, oil pressure low, ignition on, etc). The LCD 
needs to be updated with things change.  The AVR/LCD unit will be ~10 
feet from the main controller.
> 
> 2) Think home alarm/automation system. Temp sensors, door sensors, 
smoke alarms, motion detectors, etc. These "sensors" will be up to 
~100 feet away
> 
> In neither case do I need much speed. I don't have any hard number 
here, but I'd thinking tens of bits/second is all I need.
> 
> p.s. What is LIN??
> 
>  - jim
> 
> On Wed, 24 Nov 2004 14:40:04 -0000
> "Graham Davies" <YahooGroups@e...> wrote:
> 
> > 
> > --- In AVR-Chat@yahoogroups.com, James Washer <washer@t...> wrote:
> > 
> > > ... working on a system ...
> > > ... a few "remote" devices
> > > (ADC, Temp sensors, etc)...
> > 
> > People would be able to help you more if you gave us some idea of 
the
> > data rate you envision.  SPI can be pretty fast - do you need 
that?
> > The suggestion to use CAN probably assumes you do. Cheaper and 
easier
> > alternatives exist if a lower data rate would do.  An example 
would
> > be LIN.  Anyway, as people say, SPI is not right for your 
application.
> > 
> > Graham.
> > 
> > 
> > 
> > 
> > 
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