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'OT: PIC power supply'
1998\02\16@142430 by n/a

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This summer I'm going to be working on a project with a multi-drop
network of PICs connected to a Linux box. The network cable will
be about 75 long. Some of the devices will be out in a garden shed and
I would like to power them off a Ni-Cad battery/Solar battery
combination
I'm wondering if a switcher setup would be more effecient (I'm worried
about the Ni-Cad). Any comments, ideas, pointers (I love pointers :-} )?

I'm also looking for easy to find parts (1sy-2sy) and this is a hobby
project.

Thank you.

--
Neil Cherry     http://home.att.net/~ncherry    spam_OUTncherryTakeThisOuTspamworldnet.att.net

1998\02\16@152934 by Eric Smith

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> This summer I'm going to be working on a project with a multi-drop
> network of PICs connected to a Linux box. The network cable will
> be about 75 long. Some of the devices will be out in a garden shed and
> I would like to power them off a Ni-Cad battery/Solar battery
> combination
> I'm wondering if a switcher setup would be more effecient (I'm worried
> about the Ni-Cad). Any comments, ideas, pointers (I love pointers :-} )?

Why not power the nodes over the cable?  I'd use RS-485 over two-pair
cable, and use the second pair for 12V DC power.  Saves a lot of messing about
with batteries and solar cells.

Cheers,
Eric

1998\02\16@174521 by Mike Keitz

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On Mon, 16 Feb 1998 13:32:39 -0500 Undetermined origin c/o LISTSERV
administrator <.....owner-LISTSERVKILLspamspam@spam@MITVMA.MIT.EDU> writes:
>This summer I'm going to be working on a project with a multi-drop
>network of PICs connected to a Linux box. The network cable will
>be about 75 long.

Since you're going to wire all the PIC boxes together to a central unit
that has mains power, run power over the wires.  Supply about 12V and use
local regulators (78L05) at each PIC so the voltage drop in the wiring
isn't a problem.  If the PICs have to keep running when utility power
fails, a central backup battery could be used.

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1998\02\16@183239 by n/a

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Eric Smith wrote:
>
> > This summer I'm going to be working on a project with a multi-drop
> > network of PICs connected to a Linux box. The network cable will
> > be about 75 long. Some of the devices will be out in a garden shed and
> > I would like to power them off a Ni-Cad battery/Solar battery
> > combination
> > I'm wondering if a switcher setup would be more effecient (I'm worried
> > about the Ni-Cad). Any comments, ideas, pointers (I love pointers :-} )?
>
> Why not power the nodes over the cable?  I'd use RS-485 over two-pair
> cable, and use the second pair for 12V DC power.  Saves a lot of messing about
> with batteries and solar cells.

For one this I won't learn nothing if I keep taking the easy way out ;-}

Actually I've am going to do this for the initial setup. But I also want
to
experiment, I want to keep up those talents I learned in school. My job
is
in the network field and has nothing to do with my electronics degree. A
solar panel will also quench my curiosity about solar power and
batteries.
I have plans to build all sorts of weird projects some are just
mechanical
and the PICs and electronics are just used for measurements.

--
Neil Cherry     http://home.att.net/~ncherry    ncherryspamKILLspamworldnet.att.net

"Don't kill him, if he's dead he won't learn nothing" Joker (Batman II)

1998\02\16@201911 by Russell McMahon

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You could even power the system over a single pair.

1.    Analog data from a typical modem IC can co-exist on a
DC power feed.

2.    If speed is not a problem (which it almost certainly
isn't here) you could use DC signaling on the pair AND draw
power off when the data signal is high.

Example:
This is harder to explain than to do!. I'll have to get an
automated Protel to ASCII converter :-))

Power is fed from an eg 12 volt supply. Line resistance is
low over this distance - say 10 ohms. Minimum acceptable
voltage on line due to loading is, say, 7 volts allowing 2
volts headroom for a regulator at each station. Allowable
drop is therefore (12-7)  = 5 volts. If the 10 ohms was the
ONLY resistance then you could draw 5v/10r = 0.5amp. So,
place a, say, 20 ohm resistor in series with the power
supply.
Total R is now 30 ohm max. If you short the line at any
point you get a maximum of 12/20 = 0.6amp and  minimum of
12/(20+10)=0.4 amp.

Each PIC station has:
       A voltage regulator.
       A transistor which can short the line.
       The ability to sense line voltage.

If there are 10 stations drawing 10ma each you have 100ma
continuous drain. Assume it is all at the far end of the
line (worst case).
The idle voltage is then V = 12 - (0.1 x (10+20))= 9 volts.
If ANY PIC wants to transmit it shorts the line with its
transistor and ALL other stations see the line voltage drop
to a low value = logic 0. Power feed also stops during this
"logic low" condition.
Each PIC needs enough reservoir capacitor to hold up during
the worst case string of logic lows. Suitable design can
ensure that the line is always "high" long enough to keep
stations alive.

This system is wasteful of power (in this example 12x12/20 =
7 watts is dissipated in the 20 ohm feed resistor when the
closest station is transmitting) but the power can be
tailored to "just work" in your case and the feed station
can probably be mains powered. This sort of system will work
effortlessly at low baud rates (1200 baud) and can probably
be made to work at much higher ones. The stations can be
very low cost (PIC, regulator (possibly only  a zener),
small TO92 transistor (minimal dissipation off or on))

National Semiconductor once suggested something like this
with their now ancient 14469 AART transceiver IC. The
application notes may still be available somewhere. .

DIAGRAM:    Consumer Warning

The following diagram made sense in WordPad in Windows 95
using Courier font.
When copied to IE4 email it makes none.
Depending on your browser YMMV.

V+ ----
     |
    R
R <-- This R allows supply to be shorted for signalling.
R
|
|   <-- Data and Power line -->
___________________________________________________-> more
PICS
   |        |
   |      __________     ____________  |C
   |     |          |   |            |     |/
   ----- | Regulator|---|  PIC       |--RRRR--|
         |__________| | | ___________|    b|\
                    |     C       |   |E
        |     C  |   |

_______________|______|_______|_________________|___________
___
PIC will also need to sense line voltage (not shown)
C is essential to keep PIC powered during data low


{Original Message removed}

1998\02\17@003946 by tjaart

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Undetermined origin c/o LISTSERV administrator wrote:

{Quote hidden}

The Cherry Semiconductor CS212 security chip runs on an extremely
easy one-wire protocol that also powers the nodes. It is made for long
runs like you describe.

You could probably hack the protocol to work for your PIC nodes.

You can look in a Maplin catalogue (catalog), or you can look on the
Cherry site. There is a link on this page :
http://www.wasp.co.za/~tjaart/electroniclinks.html

BTW : Your name reminded me of the chip!

--
Friendly Regards

Tjaart van der Walt
EraseMEtjaartspam_OUTspamTakeThisOuTwasp.co.za
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1998\02\18@065910 by Tom Handley

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  Neil, I'm working on a water pond with a waterfall. I want the pump
to run off of batteries charged by 12VDC as well as a solar panel. I
have decided on sealed lead-acid batteries. While this is still very
preliminary, I'll be using a PIC for control. I'm sure I'll have a lot
of questions about PWM control later this spring. I'll be glad to share
my work.

  - Tom

At 01:32 PM 2/16/98 -0500, you wrote:
{Quote hidden}

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