laser activated switch

[news.verizon.net]

I'm looking for a circuit for a switch that can be activated by a standard laser pointer and nothing else. I know I could probably buy some very expensive filters to only let laser light pass through, but I'd prefer something that uses a phototransistor or photodiode that can adjust sensitivity and tune to the proper frequency and or wavelength. Anyone have any ideas? Thanks.

 

[Sir Charles W. Shults III]

Well, the wavelength thing sort of makes this tough. But, having faced
similar challenges before, I can tell you that using a number of gel type
filters from the Rosco sample book is a good place to start. Keep in mind that
it will be nowhere near as good as a nice narrow band optical filter, it can
still get a lot of the ambient light out of the way.
Start by looking in the sample book at the spectral response curves and pick
about three filters that pass your longer wave red well while blocking most
everything else.
The #19 (Fire) filter is a good, sharp cutoff type to start playing with.
Overlap that on a #93 (Blue-green) and it will cut out a huge portion of the
visible spectrum while letting roughly 50% of the laser pointer light through.
Overlapped once again, this time with a #84 (Zephyr blue) and it will cut nearly
everything out but allow red laser light to get through pretty well.
Of course, this is no substitute for a real laser filter, which can
sometimes be found for a buck or so at good surplus outlets, but if you spend a
little time experimenting with the gel filter books and their passbands, you can
get a pretty fair filter together.
You know, modulating a laser pointer is really very simple and would greatly
enhance the sensitivity of your circuit. Check my web page and you can find a
section about laser pointers there which might be helpful.
Finally, if you go just for light and no modulation, almost any cheap
phototransistor can be used as your sensor and then any low current relay (or
even a solid state relay) driven from it. But I would really rather use a
modulated pointer and a "tone decoder" or PLL to do that.

Cheers!

Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip

 

[Joe]

"Sir Charles W. Shults III" <aichipREM@OVEcfl.THISrr.com> wrote in message
news:4slPa.67318$bK5.1540723@twister.tampabay.rr.com...

You know, modulating a laser pointer is really very simple and would
greatly
enhance the sensitivity of your circuit. Check my web page and you can
find a
section about laser pointers there which might be helpful.

Sir Charles,
I checked your webpage (address below?), and could not find a reference to
laser pointers. I am interested in learning more about this. Would you mind
posting a link to the page you are referring to?

Finally, if you go just for light and no modulation, almost any cheap
phototransistor can be used as your sensor and then any low current relay
(or
even a solid state relay) driven from it. But I would really rather use a
modulated pointer and a "tone decoder" or PLL to do that.

Cheers!

Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip

Thank you,
Joe

 

[Sir Charles W. Shults III]

http://home.cfl.rr.com/aichip/CIR03.htm

There are a few circuits there, although far less than I should have. Time,
sigh.

Cheers!

Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip

 

[Bob Masta]

On Thu, 10 Jul 2003 20:27:28 GMT, "news.verizon.net"
<vze35gs5@verizon.net> wrote:

I'm looking for a circuit for a switch that can be activated by a =
standard laser pointer and nothing else. I know I could probably buy =
some very expensive filters to only let laser light pass through, but =
I'd prefer something that uses a phototransistor or photodiode that can =
adjust sensitivity and tune to the proper frequency and or wavelength. =
Anyone have any ideas? Thanks.

In addition to Chip's comments about filters, I wonder if maybe
you can do something with the output of your phototransistor
to detect laser pointer dynamics. I'm assuming here that the
pointer is hand-held, so that the spot will not be steady on the
sensor. (In fact, you may have a hard time hitting it at all!)
So you might hi-pass or differentiate the output to discriminate
against headlights, flashlights, daylight, etc.

Just a thought...



Bob Masta
tech(AT)daqarta(DOT)com

D A Q A R T A
Data AcQuisition And Real-Time Analysis
Shareware from Interstellar Research
www.daqarta.com

 

[C.M. Hobbs]

news.verizon.net wrote:

I'm looking for a circuit for a switch that can be activated by a standard
laser pointer and nothing else. I know I could probably buy some very
expensive filters to only let laser light pass through, but I'd prefer
something that uses a phototransistor or photodiode that can adjust
sensitivity and tune to the proper frequency and or wavelength. Anyone
have any ideas? Thanks.

i seem to remember a couple of kits that were a game of "laser darts".
basically, a laser sensetive bullseye (using a normal laser pointer, you
could play a game like darts). it seems to me that this would be easily
modified for your purpose, if you can find one.

i'll do some more research, i believe that they were fairly inexpensive.

regards,
chris

--
C.M. Hobbs [KD5RYO]
http://www.destroyallmachines.net

 

[Dr Engelbert Buxbaum]

news.verizon.net wrote:

I'm looking for a circuit for a switch that can be activated by a
standard laser pointer and nothing else. I know I could probably buy
some very expensive filters to only let laser light pass through, but
I'd prefer something that uses a phototransistor or photodiode that can
adjust sensitivity and tune to the proper frequency and or wavelength.

The easiest way would be to amplitude modulate the laser light (change
its intensity a couple of 1000 times a second). The modulation could
then be detected in the receiver with a bandpass filter.