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'[EE]: Mucho gracias on low current IR decoder'
2003\04\24@192739 by Alex Kilpatrick

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Last week I was soliciting help for finding a low-current IR decoder.
Several people replied with creative schemes to control the decoder via
the PIC.  Some wonderful soul, however, told me about a device that
consumes only .2 mA instead of the typical 2-3 mA.  It is from Sharp,
and the reason I never found it before was that it was classified as a
"remote control receiver," instead of an IR decoder.  However, it is
pretty much a drop-in replacement for the Panasonic IR decoder, except
it only consumes a *tenth* of the current (and power and gnd are
switched).
This device has allowed my project to go from ~3.5 mA constant current
to .4 mA constant.  This gets me down to coin battery territory, which
is drops my overall weight by a lot (I was using a 9V before).  This is
for a wearable device, so weight is a huge deal.
I wish I remembered who suggested this device, but I want to express my
sincere thanks to them and to everyone else on the list who helps out.
The PICLIST is a wonderful resource!
Alex

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2003\04\24@203419 by Timothy Box

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Alex

Glad you found it useful. In the device I used it in I got the current down
to  <80 ua (depending on lighting)

And the maths indicate 3+ years from a 1/2 AA Lithium (if you can believe
the battery rating)

Tim

{Original Message removed}

2003\04\25@005336 by Alex Kilpatrick

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> -----Original Message-----
> From: Timothy Box [spam_OUTtimTakeThisOuTspamTJBSYSTEMS.COM]
> Sent: Thursday, April 24, 2003 7:34 PM
> To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
> Subject: Re: [EE]: Mucho gracias on low current IR decoder
>
>
> Alex
>
> Glad you found it useful. In the device I used it in I got
> the current down to  <80 ua (depending on lighting)
>
How in the world did you do that?  The specs say 200 uA with no light
input.

Alex

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2003\04\25@011019 by Herbert Graf

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> > Glad you found it useful. In the device I used it in I got
> > the current down to  <80 ua (depending on lighting)
> >
>
> How in the world did you do that?  The specs say 200 uA with no light
> input.

       Probably by only having it on for certain periods of time. TTYL

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2003\04\25@023333 by Timothy Box

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Alex

As the other user said by only having it on for about a 1/3 duty.

It is however not as simple as that. The job was to look out for IR signals
that had a signal frequ of about 12 hz so by turning on the IR device, then
going to sleep with interrupts enabled you get woken when ever there is an
IR signal. After a set period the PIC wakes from its nap and turns the
device off again. When it wakes it looks to see what woke it IR signal or
sleep ending. If it was the IR signal it checks for it's validity and either
handles it or goes back to sleep.

The big problem arises in that the IR device has a period of instability
where it sets the OUT signal low for a period and then jumps around while it
stabilises. This period depends on the lighting conditions, with High Feg
flororesant lighting upsetting it most.

You could just monitor the signal and wait until it has settled but that
takes PIC power. Or you could sleep for what you find to be the longest
period that you would find this instability. The trouble with that is, this
period varies from about 15ms up to 140ms, so a lot of wasted energy could
be used unnecessarily.

So what I did was write the code to analyse the signal to establish when the
device had settled whilst spending most of its time asleep.

As the product was a security device, you could not have it being disabled
just by someone holding a TV IR remote control button down. So it can also
detect interference and identify what type of interference it was. Bad
lighting or IR jamming and react accordingly.

BTW the devices are very sensitive and I can trigger it from over 40' away.

I would see that in your application, if you were looking to set up a two
way coms between devices. One would be powered all the time and periodically
sending out signals at say 12 hz and all the time looking for a reply from
the mobile unit.

The mobile unit could do as mine did just look out for that signal using min
power when it found it could then power up full time and start some serous
coms going.

As an aside I would look at using the new 18F1320 as it is a really low
power device with just about no latency while it powers up from sleep. (the
rc clock taking over until the main one settles)


If it would help I can send you the code.

Tim




> {Original Message removed}

2003\04\27@111733 by Alex Kilpatrick

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> -----Original Message-----
> From: Timothy Box [EraseMEtimspam_OUTspamTakeThisOuTTJBSYSTEMS.COM]
> Sent: Friday, April 25, 2003 1:35 AM
> To: PICLISTspamspam_OUTMITVMA.MIT.EDU
> Subject: Re: [EE]: Mucho gracias on low current IR decoder
>
>
>
> As an aside I would look at using the new 18F1320 as it is a
> really low power device with just about no latency while it
> powers up from sleep. (the rc clock taking over until the
> main one settles)
>
>
> If it would help I can send you the code.
>
> Tim
>
Thanks, but I mainly wanted low power to be able to use coin batteries
(for weight).  I don't need extreme lifetimes.  At 400 uA, I should get
in the neighborhood of 1000 hours with two 200 mA-H coin batteries.
That is more than enough.  I would be happy if it lasted a month.

Alex

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