Laser Switch

[dfussell]

Hi All,
I am looking for a circuit that would allow a laser to close a switch. Laser would be just inches from said switch. When beam from Laser is not present the switch opens and sends a wireless signal.
Can someone help with this design?
David

 

[QuietMan]

Is there any other ambient light around? If not it expands your options, such as a LDR (electric eye, aka photocell).

 

[dfussell]

Thanks for your reply.
No other light.

 

[QuietMan]

Are you familiar with a photocell? They can be had many places, including Radio Shack. Basically they vary their resistance from a couple of ohms when exposed to light to a couple of megohms when in the dark. Add a variable resistor (pot) in series and they can be used to sense light, the output is a voltage swing. From there you can use a digital IC, 555, or a transistor to switch.

**broken link removed**

CdS Photoresistors (5-Pack) - RadioShack.com

 

[dfussell]

cool thanks.
I didn't realize that these could work with a laser?
Thank you, QuietMan.

 

[QuietMan]

Here is a possible schematic of how to use them, you can swap R2 and CDS1 to switch the voltage swing...

 

[dfussell]

Thanks again this is useful.
Merry Christmas

 

[Sceadwian]

dfussell what's the output of your laser? CDS photocells have a responce from roughly 515-730nm's

 

[dfussell]

1-2mW
Thanks

 

[Mr RB]

David Cook at RobotRoom.com already wrote up a great system, he used 2 LDRs and a comparator, so when you shine the laser at one LDR it is detected.

This is pure genius because it removes any issues of ambient light level AND it also gives you 2 sensors so it can be used for on/off or up/down remote control etc.

See here;
Robot Room: Laser Pointer Remote Control Circuit

 

[Sceadwian]

I guess I wasn't specific enough, I wasn't talking about power, I was wondering what it's wavelength is, IE what colour is it? I don't think CDS photocells will pick up an IR laser, but I'm not sure. They're very close in spectral responce to the human eye, though I think there is a bit more towards the high end.

 

[QuietMan]

Good point, I assumed we were talking a visible laser.

 

[dfussell]

Thank you Mr. RB

 

[dfussell]

Sceadwian, it's Red however, I could change it.