Laser alarm

Cad sulphide cells aren't used much anymore--I'd stick with a photodiode. If you modulate the laser and detect the AC, it'll work well day and night, unlike a CdS cell.

Cheers

Phil Hobbs

Thanks.

I got the lasers in and hooked it up for 5 minutes.

I liked that it's beam is adjustable.

It did not heat up.

Will post when I get the detector parts in. Will show what I have BEFORE I apply power. :-)

Andy

I found this. It uses less parts and does not seem to be missing info that the other project did.

What do you think?

"

Andy

I'd question the use of red tinted glasses if one is using a red laser. (that's the color you want to keep out of your eyes)

I wouldn't use a cadmium sulphide photocell, because they are prone to water damage unless they are hermetically sealed in glass. The type he shows just has a film of varnish or epoxy to protect the element and the performance of those degrades over time and humidity. I'd use an NPN two terminal photo-transistor. (emitter to ground)

You'd want some power supply if you intend to leave it on 24/7

It would be fine for a simple easy project. If the object is to learn it is ideal.

RE I apply power. :-)

at the other project did.

Like this ?

"

Sure, any one of those. The only downside is that your beam aiming has to be more precise (smaller target)

R2 will probably be on the order of 4,700 - 10,000 ohms and NOT the

A professionally designed "break-beam" detector would use a modulated light source and a detector that is able to discriminate the modulation frequency, as a way to exclude false detection.

What he's showing is similar to how it was done since the days of vacuum tubes. The thing will work fine as long as the laser light is significantly brighter than any ambient light.

Do you have a "bench" power supply and a digital multimeter? I'd consider those necessary basic stuff for this project. You can use any "wall-wart" power supply or a battery pack for power but there's some inexpensive half-way decent power supplies on Ebay. \ This one is a good one (I just assembled one for a project of mine)

They claim 2 watts at 15 volts but I wouldn't trust that, the transformer seems too small to me. It is a kit too... Easy to solder, the board is "masked." The component placement is silk-screened onto the board. The board is marked for a 100 ohm resistor and the schematic says 240 and 240 is what is supplied, but other than that, there's not much to go wrong.

digital multimeters go on sale at Harbor Freight for ~$3.00

Only caveat, don't switch through the current settings while connected across a power supply - that burns out the meter's fuse. (I had a smart high school grad working for me who went through several before he caught on - he had zero experience or training but was able to build stuff and read schematics, so I gave him projects he could handle)

I will mount it in a piece of pvc. Will adjust depth and check the resistance.

With the detector in a tube, the laser will be quite a bit brighter.

The beam is adjustable from a fine point to a wide beam.

I have both.

My buck converter is adjustable.

Andy