AVR-Chat

Hello Mr. Chuck Hackett,

A word of caution ... any voltage used where people might contact across it
must be properly installed and shielded. Any voltage higher than about
30volts is considered potentially lethal. So some careful design work is
required to study all of the possibilities and just what is required and can
be used.

Somewhere here you must define a node, it's power requirements, power cycle,
does it just need 5 volts, or does it require other voltages, and so on.
Switching regulators are inexpensive and cheap but until the requirements
are defined you don't know that even a simple 5 volt linear regulator won't
do the job without any great problem. You must start with defining the
current requirements then you can figure how to power it by an engineering
study.

I might suggest starting with a drawing of the layout of where everything is
installed, the distances, the potential copper losses and so on. It should
quickly be apparent which direction to go when the analysis and mathematics
of the whole thing is layout out in a clear and understandable fashion.

Figure out how much current each of these nodes requires, what is the
maximum, minimum, are they all on all of the time?, only when a train
approaches, or whatever. Better yet put together a little computer
simulation to see what the power requirements maximum are, what happens when
you run the train, what is the real power needed?, and so on.

Then try 12volts, 18volts, 30volts, AC or DC or if you are going to properly
shield in conduit etc, 110vAC, solar power, or whatever and so on. Study is
required here before proceeding.

Jim

----- Original Message ----- 
From: "Chuck Hackett" <egroupscdh@WhiteTrout.net>
To: <AVR-Chat@yahoogroups.com>
Sent: Tuesday, February 01, 2005 10:12 AM
Subject: [AVR-Chat] Signal System Power


>
> I'm looking at developing a signaling application for 1.5" scale ride-on
> railroads (a hobby of mine).  It involves a long signal bus (up to a
couple of
> thousand feet) based on RS-485.  I'll also need to run power to operate
> ultra-bright LEDs as well as intermittently drive a couple of low voltage,
low
> power electric motors.  The cables will typically be buried along the
track.
>
> My design will involve and AVR-based module at locations along the track
to
> detect trains present on a section of track, signal other modules about
track
> occupancy, drive local signal (light) heads and possibly low voltage
motors to
> move throw track switches.
>
> As I see it, I'll have to bury two cables along the track, one for power,
and
> one for the RS-485 signal bus (either 2-wire or 4-wire with signal ground
to
> control common-mode voltage differences).
>
> My question at the moment is what is the best way to power the devices
along the
> network.  I don't expect a large current draw at each location (module
power
> plus several ultra-bright LEDs on at once) and at locations that have
small
> intermittent motors I could place a small rechargeable battery to take the
surge
> and trickle charge it from the power bus.  Some thoughts:
>
> 1) Something like 14-3 house wire carrying 12vdc (since 12vdc is common
for
> motors, lights, etc.) but I was worried about voltage drop over 1,000's of
feet.
> Obviously there would be voltage regulators at each module for local logic
> power.
>
> 2) Same as #1 but use a higher DC voltage (48?) to reduce the current and
hence
> reduce the voltage drop.  How does one get from 48vdc to 3-5 vdc without
huge
> losses.  Cost is a factor here.  I realize that I could use a PWM
regulator but
> are there inexpensive chips for this?
>
> 3) Something like 48 VAC.  Easier to step down to a reasonable level but I
fear
> having a transformer, etc. at each module would increase costs too much.
>
> I'm looking to keeping module costs as low as possible and still have a
reliable
> system.
>
> Comments?  Other ideas?
>
> 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
>
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