What I want:
a laser beam pulsing at some frequency by a 555 to be detected with a photo-resistor detecting that frequency set by the 555.
The majority of the time the laser will not hit the sensor


What can I use as a frequency detector? can a 555 be used

What can I use to diffuse the laser beam to get a bigger sensor area?

or Is there a better way to make a laser beam sensor [bigger sensor better detecting]?

 

You can use the 555 and a gate to make a missing pulse detector, but you would probably be better off if you used something like an NE567 tone decoder.

The is probably no reason to make the beam bigger -the amount of power will remain the same no matter what you do to the beam cross section (ignoring for the moment that the optics will have losses), unless you are concerned about damaging the photo detector.

By the way, many aspects of your project are addressed at the URL below.
http://circuitschematic.blogspot.com/2011/06/ne-555-lm-567-remote-control-circuit.html

 

Thanks Dick Cappels for the reply
The tone detector was the IC I was trying to remember. I will have to research them more.

The sensor area I need is about the size of a computer sceen.
The beam laser beam will come from a 1mw laser.
I'm trying to figure out also How to have an area the size of a computer screen sense the laser beam with the least amount of photo cells as possible. By diffusing or fiber optics etc. whatever is cheapest

 

Two ideas..I remember photo resistors as being rather slow, and Fresnel lens.

 

whats the max frequency photo resistors would work? -compared to photo transistor

the only photo transistors I have are 900nm would red laser light work?

 

What are you trying to detect - obstruction of the beam by an object or reflection from it? How big is the thing you are trying to detect?

If you expand the beam, then a small object would only obstruct part of the beam, You might need multiple detectors to cope with that. Similarly, a small object can only reflect a small amount of power from an expanded beam, in which case high sensitivity will be necessary.

 

I want to detect when the beam hits the sensor.
I want to shoot a laser beam at a sensor. regular weak laser beam. Most of the time the laser will not hit the sensor. When it does I want an output.
On top of that I would like the sensor area pretty big (1ft x 1ft or bigger). So maybe if I wire up a bunch of photo resistors or transistors together the sensor will be bigger and maybe diffuse the light from an area between a photocell to the photosensor.

I suppose I could expand the beam however I need it to work at different distance(1-20 meters) so I was thinking a regular laser beam would not disperse over that distance.
but then again the sensor it hits 1x1 needs to be sensitive enough to give an output no matter where the beam hits on the sensor