I've been experimenting with detecting reflected laser pulses in the
532nm (visible green) wavelength. By modulating the pulses and tuning
a receiving circuit I've been able to get the detector to work over a
distance of several feet in a darkened room.

I'm thinking that mixing infrared laser light with the 532nm and using
IR photodetectors. Would this allow for more ambient light in the
room?

My TV remote control seems to do very well in detecting pulses from an
IR diode, even in bright sunlight - is there more to it than just the
shift to the IR spectrum? Or is the modulation a key factor in the
detector being able to "see" the remote?

Dave

On Jan 21, 11:09=A0am, Kasterborus <kasterbo...@yahoo.com> wrote:
> I've been experimenting with detecting reflected laser pulses in
the
> 532nm (visible green) wavelength. By modulating the pulses and
tuning
> a receiving circuit I've been able to get the detector to work over
a
> distance of several feet in a darkened room.
>
> I'm thinking that mixing infrared laser light with the 532nm and
using
> IR photodetectors. Would this allow for more ambient light in the
> room?
>
> My TV remote control seems to do very well in detecting pulses from
an
> IR diode, even in bright sunlight - is there more to it than just
the
> shift to the IR spectrum? Or is the modulation a key factor in the
> detector being able to "see" the remote?
>
> Dave

The modulation is a big part of it. The remotes I've worked with
(Samsung and Sony) both send 32 bits total and the last 8 bits are
sent twice, the second time inverted which helps data verification.
Both remotes continously repeat the 32 bit sequence as long as a
button is held so there's a good ghance some af the commands will get
through.

GG

"Kasterborus" <kasterborus@yahoo.com> wrote in message
news:b40b4a67-f81b-4571-bf15-986db016459e@d70g2000hsb.googlegroups.com...
> I've been experimenting with detecting reflected laser pulses in the
> 532nm (visible green) wavelength. By modulating the pulses and tuning
> a receiving circuit I've been able to get the detector to work over a
> distance of several feet in a darkened room.
>
> I'm thinking that mixing infrared laser light with the 532nm and using
> IR photodetectors. Would this allow for more ambient light in the
> room?

I guess it depends on the detectors. Some may filter out other frequencies.

For example, the TSOP11xx set of photo modules are very good at filtering
out light at other wavelengths. That is how IR works so well for TV, for
example; they filter everything except the 950nm IR between 900nm and 1um
down to -6db, and then only respond to modulation frequencies between 0.95
and 1.05 percent of the target modulation (ie, 40k).

See the figures in this data sheet:

http://www.tranzistoare.ro/datasheets/r ... 097_DS.pdf

>
> My TV remote control seems to do very well in detecting pulses from an
> IR diode, even in bright sunlight - is there more to it than just the
> shift to the IR spectrum? Or is the modulation a key factor in the
> detector being able to "see" the remote?
>
> Dave

Again, the detector is tuned to both the frequency of light, and also to the
modulation frequency of the signal.

Kasterborus wrote:
> I've been experimenting with detecting reflected laser pulses in the
> 532nm (visible green) wavelength. By modulating the pulses and tuning
> a receiving circuit I've been able to get the detector to work over a
> distance of several feet in a darkened room.
>
> I'm thinking that mixing infrared laser light with the 532nm and using
> IR photodetectors. Would this allow for more ambient light in the
> room?
>
> My TV remote control seems to do very well in detecting pulses from an
> IR diode, even in bright sunlight - is there more to it than just the
> shift to the IR spectrum? Or is the modulation a key factor in the
> detector being able to "see" the remote?
>
> Dave
They have a IR passive filter that helps reduce non IR light .
also, the modulation scheme has a lot to do with it.

Normally common mode input receivers are used with capacitor
offsets on one input so that the DC component can be nulled out
while the AC component will be visible with high gain..
they may even have a band pass filter after that stage..

This means, your modulation scheme must use a steady stream
of pulses for 1's or 0's.




http://webpages.charter.net/jamie_5"

On Mon, 21 Jan 2008 19:26:40 -0500, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:


>They have a IR passive filter that helps reduce non IR light .
>also, the modulation scheme has a lot to do with it.
>
> Normally common mode input receivers are used with capacitor
>offsets on one input so that the DC component can be nulled out
>while the AC component will be visible with high gain..

---
There are only three pins on the ones I've used: Vcc, GND, and OUT.
---

> they may even have a band pass filter after that stage..

---
Usually, all the filtering and decoding is done internally.
---

> This means, your modulation scheme must use a steady stream
>of pulses for 1's or 0's.

---
Usually, the OUT pin is pulled up to Vcc through something like 10k
and when a sufficient number of IR pulses are decoded the output goes
low and stays low for as long as the pulse train exists then, when the
pulses stop, OUT goes high after a fixed delay