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mpm
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On Mar 17, 11:24 am, John Larkin
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
Mainly, because earlier today, I purchased a new camera lens (a 500mm
mirrror), and I always make it a point to grab a couple Roscolux
swatchbooks while I'm at it.
Such as this one from BHPhoto:
http://www.bhphotovideo.com/c/product/45189-REG/Rosco_950SBLUX0103_Roscolux_Swatchbook.html
Hard to beat at $1.95 each.
I wonder if there's a gel in there that will do the job?
<jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
#2 was the first thing I thought about too.On Wed, 17 Mar 2010 05:58:20 -0500, "eeboy"
jason@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?
It's a bizarre circuit.
Some things that would help you:
1. Maximize optical path gain, which means using lenses or equivalant
to focus the transmitter and receiver at one another and exclude as
much ambient light as possible from entering the receiver.
2. Put a narrowband optical filter in front of the receiver to pass
the optical signal and reject wideband ambient light.
3. Dump the photodiode current into a tuned LC tank and amplify that
with a very low-noise device, probably a jfet. The 4069 will be about
the noisiest and least gain-predictable amplifier you can buy for a
reasonable amount of money. An LC to ground allows a lot of ambient
light signal to get dumped without saturating any amplifier stages.
4. Increase transmit power.
5. Buy Phil Hobbs' book
The problem with using a high-Q resonator is making sure it's on
frequency, and not over-doing Q to the point that the data rate is
compromised.
What's the application?
John- Hide quoted text -
- Show quoted text -
Mainly, because earlier today, I purchased a new camera lens (a 500mm
mirrror), and I always make it a point to grab a couple Roscolux
swatchbooks while I'm at it.
Such as this one from BHPhoto:
http://www.bhphotovideo.com/c/product/45189-REG/Rosco_950SBLUX0103_Roscolux_Swatchbook.html
Hard to beat at $1.95 each.
I wonder if there's a gel in there that will do the job?