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From: eeboy on 17 Mar 2010 06:58
I need to design an IR receiver which will demodulate IR input at a given
carrier frequency (~32kHz) over distances of 60-80 feet. I am not
transmitting data, simply pulses of varying length (20ms-80ms). These
pulses occur at the rate of approximately 1Hz. It is important that the
pulse length is preserved from transmitter to receiver. In other words, if
I send a 20ms pulse I expect it to be within 5% on the receiving side. The
sensor will be used outdoors so it must discriminate against ambient IR and
other sources (street lights?). I'd like to have a fairly high Q such that
'normal household remotes' operating around 38kHz are significantly
attenuated. Finally, given the device is battery powered (5V regulated) it
should consume little power (sub 1mA if possible)

I've tried using a simple IR remote receiver module (Vishay PN
TSOP85238TR). They work great indoors (~50') but are lousy outside (~8').

Now, I am not an analog guru which is why I am here to seek guidance. My
initial thoughts were to amplify and filter (bandpass) using op-amps.
However, I started googling to see what I could find on the subject and
nearly everything I found was contrary to my initial thoughts. So,
obviously I am not thinking correctly! :) However, the types of circuits I
was finding are quite puzzling to me. For example, take this circuit:
http://www.discovercircuits.com/PDF-FILES/4069rvr.pdf . Seems simple (based
on component count) although I don't quite understand how the center
frequency is set using the inductor and resistor. But why CD4069UB? I've
never seen them used as linear amplifiers before. And 2H isn't really that
practical eh?

Taking my requirements into account, what might be the best way to
proceed?


---------------------------------------
Posted through http://www.Electronics-Related.com
From: Martin Brown on 17 Mar 2010 07:38
eeboy wrote:
> I need to design an IR receiver which will demodulate IR input at a given
> carrier frequency (~32kHz) over distances of 60-80 feet. I am not
> transmitting data, simply pulses of varying length (20ms-80ms). These
> pulses occur at the rate of approximately 1Hz. It is important that the
> pulse length is preserved from transmitter to receiver. In other words, if
> I send a 20ms pulse I expect it to be within 5% on the receiving side. The
> sensor will be used outdoors so it must discriminate against ambient IR and
> other sources (street lights?). I'd like to have a fairly high Q such that
> 'normal household remotes' operating around 38kHz are significantly
> attenuated. Finally, given the device is battery powered (5V regulated) it
> should consume little power (sub 1mA if possible)

That should be doable.
You could use a 32kHz crystal to get an incredibly high Q at the
receiver end. Or a low power CMOS PLL as the decoder tuned to roughly
32kHz. Changing the crystal on an MSF 60kHz decoder might work.
>
> I've tried using a simple IR remote receiver module (Vishay PN
> TSOP85238TR). They work great indoors (~50') but are lousy outside (~8').

Have you tried changing the optics around it (and same for the
transmitter). That is by far the easiest fix on a line of sight link.
Even a simple lens hood with black internal walls may be enough to
prevent the receiver being swamped by stray light.
>
> Now, I am not an analog guru which is why I am here to seek guidance. My
> initial thoughts were to amplify and filter (bandpass) using op-amps.
> However, I started googling to see what I could find on the subject and
> nearly everything I found was contrary to my initial thoughts. So,
> obviously I am not thinking correctly! :) However, the types of circuits I
> was finding are quite puzzling to me. For example, take this circuit:
> http://www.discovercircuits.com/PDF-FILES/4069rvr.pdf . Seems simple (based
> on component count) although I don't quite understand how the center
> frequency is set using the inductor and resistor. But why CD4069UB? I've
> never seen them used as linear amplifiers before. And 2H isn't really that
> practical eh?
>
> Taking my requirements into account, what might be the best way to
> proceed?

LMV301 as the low power opamp and a 4046 to decode it afterwards.
Someone might be able to suggest a cheaper lower power way.

FWIW my advice is sort out the optics first with your current system.
Trying to see a tiny modulated AC signal sat on top of a huge variable
baseline from ambient light will always be difficult.

Regards,
Martin Brown
From: osr on 17 Mar 2010 08:16
Google "lock in amplifier".

The 32 Khz watch crystals work just fine as both oscillators and
filters, but you may have to "spoil" the Q a bit on the receive one to
get the bandwidth up a bit and kill the ringing.

Watch crystal Qs are so high that one brought within 3 foot of one
oscillating in the open air will start ringing. Besides the 32,768,
they are available at 40 and 44 khz, which is why I suggest FSK.

Can you not do FSK? instead of AM, AM for 20-80 mS is not easy, as
your receiver needs a reference to "slice" the leading and trailing
edges of the pulse. 1 second is a long time for a AM receiver if it
needs adaptive threshold of some sort.

Steve
From: osr on 17 Mar 2010 08:17
And it seems like you may need a dose of "Hobbs Salts"


http://www.electrooptical.net/www/frontends/frontends.pdf

Steve
From: Hammy on 17 Mar 2010 08:33
On Wed, 17 Mar 2010 05:58:20 -0500, "eeboy"
<jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote:

>I need to design an IR receiver which will demodulate IR input at a given
>carrier frequency (~32kHz) over distances of 60-80 feet. I am not
>transmitting data, simply pulses of varying length (20ms-80ms). These
>pulses occur at the rate of approximately 1Hz. It is important that the
>pulse length is preserved from transmitter to receiver. In other words, if
>I send a 20ms pulse I expect it to be within 5% on the receiving side. The
>sensor will be used outdoors so it must discriminate against ambient IR and
>other sources (street lights?). I'd like to have a fairly high Q such that
>'normal household remotes' operating around 38kHz are significantly
>attenuated. Finally, given the device is battery powered (5V regulated) it
>should consume little power (sub 1mA if possible)
>
>I've tried using a simple IR remote receiver module (Vishay PN
>TSOP85238TR). They work great indoors (~50') but are lousy outside (~8').
>
>Now, I am not an analog guru which is why I am here to seek guidance. My
>initial thoughts were to amplify and filter (bandpass) using op-amps.
>However, I started googling to see what I could find on the subject and
>nearly everything I found was contrary to my initial thoughts. So,
>obviously I am not thinking correctly! :) However, the types of circuits I
>was finding are quite puzzling to me. For example, take this circuit:
>http://www.discovercircuits.com/PDF-FILES/4069rvr.pdf . Seems simple (based
>on component count) although I don't quite understand how the center
>frequency is set using the inductor and resistor. But why CD4069UB? I've
>never seen them used as linear amplifiers before. And 2H isn't really that
>practical eh?
>
>Taking my requirements into account, what might be the best way to
>proceed?
>
>
>---------------------------------------
>Posted through http://www.Electronics-Related.com

Are you using the proper emitter one that is wavelength matched to you
TSOP?

I agree about the optics but unless your building these in large
quantity you likely don't have any optics.

You could try a light tube both at the transmitter and receiver.

Are you hammering the LED with it's max peak current are close to it?
Keeping in mind max package power dissipation for your LED in the
worst case ambient etc..

You can adjust the duty cycle to keep the average current to
acceptable limits. Like 10% for the carrier modulated at 40% for
continuous transmission at 1A pulses this would be about 40mA average
current. You could reduce this further by using discontinuous
transmission i.e transmit intermittently in bursts .
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