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making cheap security circuit

Hi

I am an electrical engineering student at the University of Cape Town, South Africa. I just wanted to know how to connect a circuit using 555 timer, beeper etc to the plugs in the wall. I thought of the transfromer of course, but I'm having trouble with drawing the circuit for it. I intend on using a laser with a LDR in a voltage divider to detect motion. Is it possible for someone to maybe sketch something that i can work on?

Reply to
Mack
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Try google. What you ask for is already out there. The problem is sifting through all the chaff to find it.

Look at

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simple circuit to detect a laser or other light source to use in a "break beam" detector circuit. Scroll down to "Laser Surveillance."

Likewise . . . you mention 555 you want the thing to alarm for a predetermined time? Those circuits are on the web and in the "data sheet" information for the 555.

Transformer - use a wall wart power supply

Tons of circuit sites to comb through with similar information on them.

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has a few links on it
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robot builders and model train buffs use similar circuits

Plenty of IR detector circuits out there too - substitute a visible light detector element or just incorporate some of the circuit into your design

I've designed several ir circuits that use a modulated light beam - harder to foil by just swamping the detector with white light - it only detects light that is modulated with the right frequency. I haven't used lasers for the light source but all it should take is substituting the laser for the visible LED (and reduce the power supply voltage to something the laser could live with - I pulse the diodes from a +22 volt source with peak of a half amp and average power of only 60 milliwatts)

I can email a jpg of the circuit - three integrated circuits and more complicated than the basic circuit on sam's repair web site. Just the transmitter and receiver and frequency modulation circuit - no timer or other stuff an alarm would require.

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