IR Receiver/Demodulator [Design]

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From: Tim Wescott on 17 Mar 2010 14:39

eeboy wrote:
>> 2kHz may be a bit much for this application. Can't you use a watch
>> crystal to get the uC stable? Modern ones have internal digital loops to
>> give you 8MHz or thereabouts of clock.
>>
>> Then use a watch crystal on the receive end as filter. Cheap, but may
>> not work well in really frosty temps. And the crystals have to be very
>> accurate because the bandwidth will be in the order of 10-20Hz. Anyhow,
>> just as an idea to play with in case all else fails.
>
> A bit much in the sense that it's not selective enough? Unfortunately the
> micro in this app has no such internal loop.
>
If the selectivity of the crystal is a problem, it's that it's too
selective.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

From: eeboy on 17 Mar 2010 14:57

>If you must use that one for whatever reason then you are between a rock
>and a hard spot. Can you use a 8MHz crystal? Or at least a resonator?
>

Indeed... I can utilize an 8MHz crystal oscillator. I sacrifice about 20uA
supply current by doing so but it is an option.

---------------------------------------
Posted through http://www.Electronics-Related.com

From: Hammy on 17 Mar 2010 15:07

On Wed, 17 Mar 2010 10:19:39 -0700, John Larkin
<jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote:

>
>Reducing the duty cycle of the 32 KHz drive will directly reduce
>equivalent transmit power. 50% is ideal; then drive it with all the
>current it can stand.
>
>John

I haven't used IR in over a year but I remember getting pretty good
range with a TSAL6100 and a PNA4602M detector. Carrier pulsed at 10%
and 1amp; modulated at 40%.

If its a remote then its not continuous transmission so battery power
shouldn't typically be an issue.

Its odd that the LTE-5228A datasheet doesn't spec radiant intensity
for high current pulses. Maybe its not the best emitter for the
job.They only provide specs for 20mA that's useless for long range
transmission.If an emitter is rated for 2A you would figure they show
some specs at higher current pulses. When they don't it makes me
wonder.

For example here is the datasheet on the tsal6100.

http://www.vishay.com/docs/81009/tsal6100.pdf

From: markp on 17 Mar 2010 16:19

"eeboy" <jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote in message
news:ZO-dnd5UPcu9uzzWnZ2dnUVZ_qmdnZ2d(a)giganews.com...
> >If you must use that one for whatever reason then you are between a rock
>>and a hard spot. Can you use a 8MHz crystal? Or at least a resonator?
>>
>
> Indeed... I can utilize an 8MHz crystal oscillator. I sacrifice about 20uA
> supply current by doing so but it is an option.
>
> ---------------------------------------
> Posted through http://www.Electronics-Related.com

I believe the AVRs (ATtiny series I'm thinking of) have internal oscillators
that can be calibrated via software (you would do that once at the testing
stage). There's still a small variation with temp/voltage but the absolute
frequency would be closer. Worth looking at them and comparing prices and
current comsumption. Also AVRs are single clock per instruction which could
mean you can knock the frequency down (programmable via an internal
register) and that would save more power.

Mark.

From: Jim Thompson on 17 Mar 2010 16:41

On Wed, 17 Mar 2010 13:12:36 -0500, "eeboy"
<jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote:

>>>This sounds interesting to me. So, as I understand it with ambient light
>>>(DC) I'll have a low impedance path to ground. However, when I am
>wiggling
>>>close to the point of resonance I'll begin to see a voltage develop
>across
>>>the LC tank as the impedance increases. Correct?
>>>
>>>How is the Q of the tuned circuit adjusted?
>>>
>
>>
>>How much can your 32kHz vary? Modulation rate (pulse widths that need
>>to be discerned)?
>>
>
>I wasn't exactly sure what you were specifically asking so hopefully the
>answer is in here somewhere... :)
>
>First off, I am actually free to choose any carrier frequency I want. I
>chose 32kHz because it was lower than what most of the consumer remotes use
>(36-40kHz from what I can tell). Presumably that will make life easier on
>me. The transmitter is controlled by a dirt cheap microcontroller which
>utilizes a 8MHz RC oscillator as a time base. It's fairly easy to adjust
>the transmitter carrier. Given that it is RC based the timing can vary by a
>few percent with temperature. I've been doing some tests (heating
>up/freezing the transmitter) and can say that at the extremes I am within
>3% of the base (room temperature). There will also be a variation from
>device to device of course. Although my testing of the variation is not
>complete, given the above, I'd like to have a 2kHz window or so.
>
>
So anything tighter than about a Q=10 could cause you problems.

...Jim Thompson
--
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