Frustration

While I have not given up on the laser alarm,

I would like to explore other options.

Does anyone know of an alarm project that they know works pretty consistently?

Like was said, nothing works right out of the box.

It does not necessarily have to use a laser.

It can be a motion detector

or use an PIR senser.

Thanks.

We do big, complex circuit boards that work first time, and can be sold, without prototypes. Spice helps a lot, as do design reviews.

Civil engineers get things right first time, programmers never. We can if we try.

I know you can buy what you want ready-made on ebay with a claimed range of ~100 meters for about $10 and up.

And you might consider a "retro reflective" type beam. (one box has the transmitter and receiver and it is aimed at a reflector, like you see on automobiles) - that way one power supply and no wires to two boxes.

I'd advise sticking to one method/schematic and seeing it through until you have it working.

John Larkin has the right idea, get a flashlight, LDR and your meter and play with it. From there it would be relatively easy to add a transistor and relay or buzzer.

With a sensitive enough relay and hefty enough LDR (high current capacity) the LDR could work the relay directly. (they use that technique on some dawn-to-dusk street lighting)

BTW with a transistor and relay you could even make the relay self-latching if you want the alarm to stay on once tripped.

You have to learn- it seldom works the first time. Once you know what you are doing, a non-working project is no big deal because you will have the knowledge and confidence to make it work. That can actually be fun and very satisfying.

I was working prototyping power supplies at this one place. Hit the switch and things got really exciting. Smoke, fire, noise... and when we put the fire out and the smoke cleared, my boss who was standing right behind me says in a calm voice, "Well, what have we learned from this?" like it was nothing.

I should hope so, too. That's your profession! I'm only speaking as a long-time hobbyist.

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I really wouldn't. The concept you are currently working on is about as simple as it gets. Don't give up on it. Stick with it, get it working with or without help and you'll be very glad you did. IF you're serious about learning, that is.

With computer aided design the electronics, mechanical layout, everything, can be predicted with enough confidence to do that.

Good thing too, because surface mount components are best left to machines.

Can you post a picture of the assembly so that someone can check that you have understood how to put the circuit together?

The ne555p chip got fried. I got 0 volts at pins 3 and 6.

I have one left.

If someone can step me thru this, I will risk my last chip.

Andy

Those 555s are cheaper than french fries. Don't sweat it. If you're not blowing stuff up, you're not learning anything (in the early stages anyway).

LT Spice is free and (usually) makes a pretty good prediction of what most circuits will do.

It also helps train your instincts, about what affects what, which is helpful on the real thing.

I am running Linux Ubuntu.

Will see if I can find it.

Andy

From the nonsense that you post, I can see why you believe that. If it were true we would still be trying to develop the first tubes, and using Alexan derson Alternators to transmit Morse Code.

It's a free download from Analog Devices (Nee Linear technology) It runs fairly well in wine. it has the advantage that most everone here has convenient access to it, and that its save format is ascii so can easily be posted on usenet.

gEDA and Kicad may also be worth a look.

LTspice works very well on Linux using Wine.

Cheers

Phil Hobbs

Are you on a desert island? 555s in DIP packages cost pennies, and you can have them in a day.

Cheers

Phil Hobbs

Hmm, I'm too lazy to check the wires... (and don't know the 555) How about some capacitance (0.1uF) across the supply rail. Maybe put some resistance in the power input to limit current.. ~ 100 ohms?

How much current does the beeper draw when it's on?

Here's something done with a comparator or opamp.

(the lower circuit scribble) Comparator could be LM339 or similar.. but then needs a pull up resistor on the open collector output.

George H.

I believe I have the circuit working. I had to replace the piezo buzzer with a led.

It now lights up in ambient light and turns off when I shine a laser on it.

I read that I need a field effect transistor in order to drive a buzzer.

Is that true?

Andy

First think, then act.

Well it depends on the buzzer and the 555 (or other IC) output current. (you have to read all the spec sheets) But if there is not enough current.. then you can add some current gain with a transistor (or a tube, or a relay, or...) it doesn't 'have' to be an FET.

George H.