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'[PIC]: Anyone run PIC on 6V lithium camera batts?'
2002\02\18@205416 by Paul Gaastra

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I'm using a PIC16F628 powered by 6V lithium batteries (KL2CR5).
When new their open circuit voltage is 6.5V.  The max Vcc in the
specs for a 628 is 5.5V.  I use two 1N4007 equivalents to drop the
battery voltage down to below this.  Does anyone ignore the spec
and use just one diode or no diode at all?

I didn't use a switching supply because I was pushed for time.  The
device has to last 5 years on a battery and I didn't want to spend
time calculating which would be the best solution.


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2002\02\18@223301 by Gabriel Caffese

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I have used a 16F84 with that kind of battery, and had no problem at all.
Don´t know about F627-

  Gabriel.-

{Original Message removed}

2002\02\18@225358 by Jinx

face picon face
> The device has to last 5 years on a battery and I didn't want
> to spend time calculating which would be the best solution

As I found out/realised recently, diodes use power. If you
drop the 6V battery voltage by ~15%, that's  ~15% of battery
power wasted. Are you able to get the micro (eg an LF) to
run on just one battery that requires no voltage dropping ?

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2002\02\18@231150 by David Duffy

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At 04:53 PM 19/02/2002 +1300, you wrote:
> > The device has to last 5 years on a battery and I didn't want
> > to spend time calculating which would be the best solution
>
>As I found out/realised recently, diodes use power. If you
>drop the 6V battery voltage by ~15%, that's  ~15% of battery
>power wasted. Are you able to get the micro (eg an LF) to
>run on just one battery that requires no voltage dropping ?

But it still makes no difference to the mAH rating right?
It just means that the battery is 4.8V at the same current
rating as far as the micro is concerned. The current drain
on the battery is still exactly the same. The *power* (V x I)
consumption from the battery will be higher than the micro
uses - the diodes make up the difference. Only a switching
regulator will reduce the current on the battery side of the
voltage dropping circuitry. (not counting the switching reg's
current requirements) All up, the diodes way may be the
best/easiest way to go with a 6V battery.
Regards...

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2002\02\19@003132 by Jinx

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> the diodes make up the difference

That's important. 5 years is a big ask for a battery supply.

Anything at all that can be got rid of or not used in the first
place will help get you to that 5 years

There is no particular reason to always use a PIC at 5V. As
you know, they will function quite happily down to 3V and the
LF627/628 down to 2V. And 2V is a pretty knackered Lithium

There are probably 5V devices hanging off the PIC, and that
can be overcome. Maybe they can have their supply, and give
the PIC its own battery

If you have any more details Paul - current, sleep, circuit etc -
that would be helpful

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2002\02\19@013259 by Matt Pobursky

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The approach I like to take is to use a very low quiescent
current (micropower) low-dropout regulator, like the T.I. TPS7250
to keep the battery voltage regulated. It uses a P-channel mosfet
as the pass device and therefore uses very little current for
regulation (unlike most Bipolar linear regulators). The PIC
supply is regulated to 5V, then when the voltage drops below 5V
the regulator drops out of regulation and just passes whatever
battery voltage is present. If safe shutdown is required below
some minimum voltage, a low power supervisior circuit like a
Maxim MAX810 can be used to hold the PIC in reset when the
batteries are deemed discharged. I prefer to use a supervisor
circuit (if at all possible) to guarantee reliable startup and
shutdown. You might also use a regulator that has a micropower
comparator onboard to provide a PIC reset function.

If you were to use the "LF" version of the PIC, you could
probably use a 3.3V (or lower) regulator to run the PIC until the
batteries are completely discharged. I haven't looked at the
discharge curves of your battery, but you should be able to come
up with a circuit that "drains them dry"!

Using dropping diodes is bad as you can never "fully drain" the
battery due to the diode voltage drops -- any battery power lost
as drops across the diodes is wasted. You want every uA of
current possible going to the PIC and nowhere else.

Matt Pobursky
Maximum Performance Systems


On Tue, 19 Feb 2002 14:53:26 +1300, Paul Gaastra wrote:
{Quote hidden}

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2002\02\19@082643 by Olin Lathrop

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> Does anyone ignore the spec and use just ...

Let's not go there.


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2002\02\19@103122 by Drew Vassallo

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>I'm using a PIC16F628 powered by 6V lithium batteries (KL2CR5).
>When new their open circuit voltage is 6.5V.  The max Vcc in the
>specs for a 628 is 5.5V

I have no idea what your application is, but if it would fit in a 16F84, the
maximum spec for that chip is 6 V.  The "absolute maximum" rating is listed
at 7.5 V, so you might be able to push it with a 6.5V source, especially
since a battery should drain down quickly anyway.

People are generally vehemently opposed to overdriving chips, so beware.
However, I've often run chips at .5V over spec without any visible problems.
 That's not to say it's RIGHT, it's just a fact.  Most of my stuff is hobby
work, so I guess it wouldn't matter much to me if I fried a chip here or
there.  Your application may be different.  It's up to you.

>I didn't use a switching supply because I was pushed for time.  The
>device has to last 5 years on a battery and I didn't want to spend
>time calculating which would be the best solution.

From this statement, it sounds as if your application is not a critical one,
so you may be able to overdrive your chip.  If not, then why wouldn't you
spend a few hours and calculate the best power supply option?  Especially
for a product that must last 5 years.

--Andrew

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2002\02\19@142207 by Jinx

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Paul, any chance of supplementing the battery with a
small solar cell ? I see from your address that you're
in NZ, Dick Smith do some cheap low-end ones. That
may help you get over the consumption problem and
allow you to use a regulator if you can't run the circuit
on one 3V Li cell

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2002\02\20@145008 by Paul Gaastra

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<color><param>0100,0100,0100</param>Thanks for all the useful comments on the 6V lithium.


Perhaps I should explain a few things.  The only reason why I'm
using that particular battery is because it's long lasting, high
capacity and readily available.  I didn't choose it myself so maybe
there are some good alternatives less than 5V and then I wouldn't
use any regulation at all.  I know there are 4.5V Duracel batteries
(MN1203) that cavers use.  Maybe if they had a 5 year shelf life
that would be the answer.


The circuit is a bait dispenser and will live in the bush, so solar is
not an option.  The battery has to be capable of supplying 3A in
short 3 second bursts once in a while.


The reason I was in a hurry is because prototypes had to be ready
for a trial, but now that rush is over I have time to perfect the final
version.


I liked </color><FontFamily><param>Arial</param>Matt Pobursky's suggestion of that TI TPS7250 low drop out
regulator except that its quiescent current is 180uA.  My circuit
draws 290uA on average so I think the two diodes would waste
less energy (haven't done the sums).  I see that it has a 0.5uA
sleep state so maybe I could work out something there.<color><param>0100,0100,0100</param><FontFamily><param>Architect</param>



<nofill>

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2002\02\20@153848 by Jinx

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You'll see from the graph on this page that you probably don't
have much of a chance to get 5 years at 290uA, even more so
with the occassional 3A blast.

http://www.rayovac.com/busoem/oem/specs/lith7.shtml

It would be a good idea to have a separate battery to supply
the 3A. I think Lithiums are the best choice vis a vis shelf-
life and self-discharge. As you say, they are long-lasting, but
only if you aren't drawing any current ;-) Putting whatever you
can to sleep is definitely a good idea

==============================================

By the way, anyone notice that Google's graphic has been
changing in step with the events at the Olympics ? Cute

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2002\02\20@160534 by Jinx

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> good alternatives less than 5V

I still think you should consider an LF PIC and 3V supply. One
or more Lithiums in parallel. They aren't the biggest batteries
in the world in mAh, and I realise the Rayovac page concerned
button cells. You may have a monster of a cell

> The circuit is a bait dispenser and will live in the bush, so
> solar is not an option

Thermal pile ? Small windmill (remote of course) ? Can't you
position a solar cell somewhere up a tree and use the battery
at night or back-up on dull days ?

> low drop out regulator

As the circuit is drawing only 290uA, it's well within the capabilities
of the PIC pins to supply that much to other ICs and sensors. If
you do decide to use the 3V option, that eliminates the need for
a regulator. That way you can turn off the entire circuit apart from
the PIC, and only power-up when you have to

> the two diodes would waste less energy

Whatever your PIC uses, the two diodes will consume 15% of
that in heat (assuming a drop from ~6V to ~5V). It doesn't sound
like much in absolute terms (15% of a few uA), but it's the same
difference between 6 years and 5 years. Sounds worse when
you look at it that way

> I see that it has a 0.5uA sleep state

Ideally it has, in practise you may only get reasonably close. On a
bad day, nowhere near it by a factor of 1, however hard you try.

Over-engineer. 5 years is a long time to wait for a flop

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2002\02\20@160539 by Eoin Ross

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Why isn't solar an option? Yes it is darker in a temperate rain forest than the plains - you'd get a lower output from the cell but it would still charge the battery somewhat.

Sounds like a good project for nuking the possums.
I enquired about low current regulators a while ago - someone mentioned an SMD from Seiko - can't remember the part # - but it was below double digit microamps!
<color><param>0100,0100,0100</param>Thanks for all the useful comments on the 6V lithium.


Perhaps I should explain a few things.  The only reason why I'm
using that particular battery is because it's long lasting, high
capacity and readily available.  I didn't choose it myself so maybe
there are some good alternatives less than 5V and then I wouldn't
use any regulation at all.  I know there are 4.5V Duracel batteries
(MN1203) that cavers use.  Maybe if they had a 5 year shelf life
that would be the answer.


The circuit is a bait dispenser and will live in the bush, so solar is
not an option.  The battery has to be capable of supplying 3A in
short 3 second bursts once in a while.
The reason I was in a hurry is because prototypes had to be ready
for a trial, but now that rush is over I have time to perfect the final
version.
I liked </color><FontFamily><param>Arial</param>Matt Pobursky's suggestion of that TI TPS7250 low drop out regulator except that its quiescent current is 180uA.  My circuit
draws 290uA on average so I think the two diodes would waste
less energy (haven't done the sums).  I see that it has a 0.5uA
sleep state so maybe I could work out something there.<color><param>0100,0100,0100</param><FontFamily><param>Architect</param>

Paul Gaastra      email:RemoveMEpgaastraspamTakeThisOuThortresearch.co.nz
BioEngineering Technologies, HortResearch
Private Bag 3123            phone +64 7 8584745
Hamilton, NEW ZEALAND         fax +64 7 8584705
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2002\02\20@160907 by Eoin Ross

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Should've found this BEFORE I sent the last message.

http://www.seiko-usa-ecd.com/intcir/products/power/s812c.html

· Low current consumption
  Operating current: Typ. 1.0 µA,
                              Max. 1.8 µA (3.0 V)
· Output voltage: 2.0 to 6.0 V (0.1 V step)
· Output voltage accuracy: ±2.0%
· Output current:
  50mA capable
    (3.0 V output product, VIN=5 V)*
  75mA capable
    (5.0 V output product, VIN=7 V)*
· Dropout voltage:
  Typ. 120 mV (VOUT = 5.0 V, IOUT = 10 mA)

Also comes in TO-92

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2002\02\20@163408 by Matt Pobursky

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Yeah, that was just an "off the top of my head" suggestion as I'd
used that family of parts in the past. I believe that Maxim has
some LDO's that use significantly less quiescent current. Toko
would also be a good source to explore. As I recall, the reason
we used the T.I. part was that the Iq was not a problem (we were
shutting down the regulator and when it was running the load
current was ~20mA, so the Iq was a negligible percent) and it was
cheaper than anything else available at the time.

There are some very good parts out there these days specifically
targetted at extending battery life. I'll bet you can find a good
one that will fit your operating current requirements. Good luck
in your search.

Matt Pobursky
Maximum Performance Systems

On Thu, 21 Feb 2002 08:43:41 +1300, Paul Gaastra wrote:
>
>I liked Matt Pobursky's
>suggestion of that TI TPS7250 low drop out regulator except that
>its quiescent current is 180uA.  My circuit draws 290uA on
>average so I think the two diodes would waste less energy
>(haven't done the sums).  I see that it has a 0.5uA sleep state
>so maybe I could work out something
>there.

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2002\02\20@164455 by Matt Pobursky

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Oops, meant to add -- your application sounds like a perfect
match for letting the PIC sleep most of the time and periodically
waking it up to check for input triggers (if you have one?) or a
timer based event.

If you use an external CMOS "wakeup circuit", you can probably
get your standby current down to well less than 100uA and run it
directly from the battery voltage. I've used the CD4060 counter
and RC oscillator to periodically power up a PIC. You can use one
of the counter outputs to enable a LDO regulator.

You should be able to stretch your battery life significantly
either way.

Matt Pobursky
Maximum Performance Systems

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2002\02\20@164920 by Jinx

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What's the battery model number btw Paul ?

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2002\02\20@171243 by Olin Lathrop

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>>
The circuit is a bait dispenser and will live in the bush, so solar is not
an option. <<

Sounds like a great application for solar.  You don't need full sunlight to
get *some* power out of solar cells.  Since your circuit only draws 290uA
average, just a little assist will go a long way to save battery life.

By the way, 290uA for 5 years comes out to 12.7 Amp-hours, and doesn't take
into account battery self discharge or shelf life.  That's a pretty beafy
battery, although I'm not that familiar with what's available in lithium
cells.

Also, how often does the bait reservoir need to be refilled?  It's hard to
imagine (but possible, I suppose) that this bait dispenser can be filled
with a 5 year supply of food that won't perish while sitting in a bush
somewhere.  If someone has to go refill the container, they could just as
well replace batteries while they're at it.  Either you haven't thought this
thru or there is a lot your not telling us.


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2002\02\20@171247 by Rick C.

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I agree that its wasteful to use a linear regulator to run your pic on 5
volts especially with the LDO consideration. Also the efficiency close
to 50% if using a 9 volt battery. Wasteful! Three AA's work sufficiently
but not in all cases. Bulky too.

I just stumbled on some really nifty SMR's (switched mode regulators) in
smt and dips. The MAXIM MAX761 and MAX738A.
pdfserv.maxim-ic.com/arpdf/MAX761-MAX762.pdf
http://pdfserv.maxim-ic.com/arpdf/MAX1684-MAX1685.pdf

Also the Linear Tech devices are also a good choice.
http://www.linear-tech.com/prod/prod_home.html?product_family=power

With efficiency between 92% and 96%, this may be a reasonable
alternative. Quiescent currents about 150ua and shutdown about 1ua. The
only drawback is the possibility of noise generated by the switcher and
the higher parts count.

One nice thing is that most of them will take voltages from 3 to 16+
volts to achieve a 5 volt output.

I will be throwing together some prototypes to see if they will meet my
needs and post my results here if I feel there may be some interest. My
goal is something that won't exceed the real estate of a TO220 pkg, and
continue to squeeze all I can get out of a dying battery.

Rick

Matt Pobursky wrote:

{Quote hidden}

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2002\02\20@172734 by Olin Lathrop

face picon face
> Thermal pile ?

There's an idea! <grin>  Perhaps you can find some "loose" radioactive
strontium or whatever in one of those toy countries on the edge of civilized
Europe.


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2002\02\20@174311 by Dave Dilatush

picon face
Paul Gaastra wrote...

>My circuit draws 290uA on average...

The battery you cited has a capacity of 1440 milliamp-hours; at a steady
drain of 290uA, that works out to just under 5000 hours, or about 7
months.  That's a long way from 5 years...

Dave

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2002\02\20@181247 by Jinx

face picon face
> > Thermal pile ?
>
> There's an idea! <grin>  Perhaps you can find some "loose"
> radioactive strontium or whatever in one of those toy countries
> on the edge of civilized Europe

Australia maybe, uranium all over the place. And A-bomb sites
too. NZ is staunchly nuclear-free, I'm afraid lumps of isotopes
unlikely to be found in the bush that Paul's unit will be in

I was thinking more along the lines of hot ambient air and
cold streams for a temperature differential, although you'd
have to be a little lucky and a little more hopeful than I am to
actually try it

Any chance at all of using the Americium from smoke
detectors to generate small voltages, or is that an "end of
career" experiment ?

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2002\02\21@035324 by Alan B. Pearce

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>The circuit is a bait dispenser and will live in the bush, so solar is
>not an option.  The battery has to be capable of supplying 3A in
>short 3 second bursts once in a while.

Do you expect your supply of bait to last 5 years? I would have thought that
whoever replenishes the bait could also do a battery swap.

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2002\02\21@040145 by Alan B. Pearce

face picon face
>Perhaps you can find some "loose" radioactive
>strontium or whatever in one of those toy countries on the edge of
civilized
>Europe.

New Zealand does happen to have some radioactive stuff available as an ore
source somewhere in the South Island. I suspect it won't be worth trying to
get enough for a thermal pile however :)

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2002\02\21@060751 by Jinx

face picon face
> Do you expect your supply of bait to last 5 years? I would
> have thought that whoever replenishes the bait could also
> do a battery swap

You know what people are like though Alan. Changing the
bait they can cope with. But anything "technical", ooh, that's
another matter altogether, no matter how times you assure
them "Look, this all you have to do". You'd have to make
the replacement procedure (almost ridiculously) easy

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2002\02\21@062048 by Alan B. Pearce

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>You'd have to make
>the replacement procedure (almost ridiculously) easy

I would have thought that having the bait in a box, complete with a new set
of electronics etc, so all they have to do is lift up the old box, set the
new one down..... do it on the end of a rope from a helicopter..... take the
old box away to refill back at base.... 8)))

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2002\02\21@095859 by Dale Botkin

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On Thu, 21 Feb 2002, Alan B. Pearce wrote:

> I would have thought that having the bait in a box, complete with a new set
> of electronics etc, so all they have to do is lift up the old box, set the
> new one down..... do it on the end of a rope from a helicopter..... take the
> old box away to refill back at base.... 8)))

Seen this done...  now don't laugh.  At work there are little air
fresheners in the restrooms.  It's a simple little low-speed fan driven by
a D cell that blows air over a little gel type scent blob.  The
replacement gel thingie is a molded plastic snap-in unit that includes a D
cell.  Replace the scent and battery at the same time.  In this particular
application the polarity doesn't matter, but it could jsut as easily be
keyed to only go in one way.

Dale

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2002\02\23@195503 by Graham Medlands

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This is probably a silly idea but how about a small coil that picks up stray rf radiation, rectify it and pump up a low leakage electrolytic, this could be used in conjunction with the battery,

Graham

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2002\02\23@221301 by Jim

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face
Perhaps string a long enough wire to pick up
some AM broadcast station energy (remember those
early 'crystal' sets we played with as kids?)

- otherwise out in the bush there most likely
isn't going to be enough RF power from TV, FM
broadcast (or even cellular transmissions) to
work with.

If, by some chance you *did* cite your gear near
a 'healthy' RF source - this would be a potential
(forgive the EE punditry) source of DC! (It still
might require a few 'tricks' to pull it off
though.)

Jim


{Original Message removed}

2002\02\24@120753 by Olin Lathrop

face picon face
>>
This is probably a silly idea but how about a small coil that picks up stray
rf radiation, rectify it and pump up a low leakage electrolytic, this could
be used in conjunction with the battery,
<<

Hmm.  If you're close enough to a major transmitter and you can put up a
decent antenna and protect it from lightning, etc, then it's at least
theoretically possible although rather unlikely to work in practise.

When I was a kid I had a crystal radio.  The strongest signal came from an
AM transmitter about 25 miles away that put out 50KW at 1.03MHz.  My antenna
was about a 50 foot horizontal wire strung between my window and a post
mounted to a tool shed.  This station (WBZ, Boston Massachusetts) came in
well enough to produce quite reasonable volume in the headphones.  One time
I hooked the output to an audio transformer and powered a small 3 inch
loudspeaker with it.  It wasn't very loud, but you could understand what was
being said with the speaker on the table if the room was quiet, but
otherwise you wouldn't notice it was on.  It was also useful for annoying my
brother by leaving it on at night.  He wouldn't notice it accross the room
in his bed until everything was quiet and he was trying to get to sleep.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, .....olinspam_OUTspamembedinc.com, http://www.embedinc.com

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2002\02\25@062858 by Alan B. Pearce

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>This is probably a silly idea but how about a small coil that picks up
stray rf radiation, rectify it >and pump up a low leakage electrolytic, this
could be used in conjunction with the battery,

Probably work in an urban environment, but the specific project was going to
be out in the remote bush. This would cause your scheme to fail in two
ways: -

1. Remoteness - likelihood of strong enough RF to get charge into batteries
is not high.

2. All that green bush around will absorb RF.

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2002\02\25@104123 by Martin Peach

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face
> >>
> This is probably a silly idea but how about a small coil that picks up
stray
> rf radiation, rectify it and pump up a low leakage electrolytic, this
could
> be used in conjunction with the battery,
> <<
>
> Hmm.  If you're close enough to a major transmitter and you can put up a
> decent antenna and protect it from lightning...

How about collecting some electrons from the lightning? Some kind of
capacitor and diode arrangement to charge a battery. There's far more energy
available there, the trick is to collect as much of it as possible in the
nanoseconds available, and to avoid collecting a direct hit. A low-leakage
cap with several thousand volts on it could trickle-charge a nicad via some
current regulator that can cope with the stress...
/\/\/\/*=Martin

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2002\02\25@111450 by Jim

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face
A construction project and other useful data
relating to "crystal" receiving sets on the
AM (MW) broadcast band:

http://w3.one.net/~charlie/contest/paul.html

Jim


{Original Message removed}

2002\02\25@113211 by Jim

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face
It should be noted that the author of this
crystal set construction article demonstrates
it's ability to light an LED at the bottom
of the page and he also incorporates a signal
strength meter utilizing a 30 uA movement
with three ranges - the highest being 15 volts.

Jim

{Original Message removed}

2002\02\25@132924 by Eoin Ross

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face
Thunderstorms in New Zealand are not as frequent as what I have observed to be the case in the USA (Ohio)

Would be interesting to see if/how it could be done. I believe Nikolai Tesla had some device that picked up electricity from the atmosphere using a tank type circuit - maybe an urban myth/mad scientist story though.
If the device is to see service on the west coast of the Sth Island I don't know that there'd be much RF to pick up for power ... there's maybe 2-3 AM stations and 3-4 FM and 2-3 TV transmitters around (and the area is rather mountainous) The island is about the size of Ohio and has about 1,000,000 people on it.


>>> RemoveMEmartinrpspamspamBeGoneVAX2.CONCORDIA.CA 02/25/02 10:40AM >>>
> >>
> This is probably a silly idea but how about a small coil that picks up
stray rf radiation, rectify it and pump up a low leakage electrolytic, this
could be used in conjunction with the battery,
> Hmm.  If you're close enough to a major transmitter and you can put up a  decent antenna and protect it from lightning...

How about collecting some electrons from the lightning? Some kind of
capacitor and diode arrangement to charge a battery. There's far more energy available there, the trick is to collect as much of it as possible in the nanoseconds available, and to avoid collecting a direct hit. A low-leakage cap with several thousand volts on it could trickle-charge a nicad via some current regulator that can cope with the stress...
/\/\/\/*=Martin

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2002\02\25@161703 by Martin Peach

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Maybe there you could look into geothermal via thermoelectric devices...
/\/\/\/*=Martin

----- Original Message -----
From: "Eoin Ross" <TakeThisOuTerossspamspamCHEMSTATION.COM>
To: <PICLISTEraseMEspamMITVMA.MIT.EDU>
Sent: Monday, February 25, 2002 1:26 PM
Subject: Re: [PIC]: Anyone run PIC on 6V lithium camera batts?


Thunderstorms in New Zealand are not as frequent as what I have observed to
be the case in the USA (Ohio)

Would be interesting to see if/how it could be done. I believe Nikolai Tesla
had some device that picked up electricity from the atmosphere using a tank
type circuit - maybe an urban myth/mad scientist story though.

If the device is to see service on the west coast of the Sth Island I don't
know that there'd be much RF to pick up for power ... there's maybe 2-3 AM
stations and 3-4 FM and 2-3 TV transmitters around (and the area is rather
mountainous) The island is about the size of Ohio and has about 1,000,000
people on it.



>>> RemoveMEmartinrpEraseMEspamspam_OUTVAX2.CONCORDIA.CA 02/25/02 10:40AM >>>
> >>
> This is probably a silly idea but how about a small coil that picks up
stray rf radiation, rectify it and pump up a low leakage electrolytic, this
could be used in conjunction with the battery,
> Hmm.  If you're close enough to a major transmitter and you can put up a
decent antenna and protect it from lightning...

How about collecting some electrons from the lightning? Some kind of
capacitor and diode arrangement to charge a battery. There's far more energy
available there, the trick is to collect as much of it as possible in the
nanoseconds available, and to avoid collecting a direct hit. A low-leakage
cap with several thousand volts on it could trickle-charge a nicad via some
current regulator that can cope with the stress...
/\/\/\/*=Martin

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2002\02\27@053351 by Alan B. Pearce

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Those of you clever guys running things at very low power may like to peruse
the newest issue of the Maxim Engineering Journal. There is an article in it
called "Lithium coin-cell batteries: predicting an application lifetime",
refers mostly to using Dallas devices that incorporate these cells, but has
handy looking graphs as well.

I get a paper copy of this journal, but I believe it is also available on
the Maxim web site.

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