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Need help in building an alarm circuit

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New Member
i need some help in making a circuit diagram for an alarm circuit with a tone generator together with it. my idea here is that if i enter the house and the alarm is triggered if not being switch off in a minute, it will automatically call my mobile and tell me that someone is at the house. i need some assistance in making the proper circuit diagrams.


New Member
Dunno about this one, you'd need a phone dialer, and if you want a voice, you'll need about 20 more parts, a free wall jack with the wiring run through the wall, a counter, a keypad programmed with a memory, an audible alarm, probably a proximity switch, or motion sensor.

After that, start fiddling, because I doubt anyone here has gone to such extremes with home security, a laser usually works better anyway :twisted:


New Member
Hello Danny,

The web is full of good sensor and alarm circuits, look around to see what would work best for you and your home.
It is a bit difficult for me to advise you because I am in England and I do not know the electronic suppliers in your area.

I have a couple of suggestions though
One is to find an old line connected telephone with memory dial buttons and link one of the stored number buttons to the alarm circuit or if you can get hold of a old mobile phone to open up, these often have a option to dial a number from a single key press,if you can find one that uses a pre-paid scheme it wont cost anything to just ring another phone and it is immune to would be thief cutting telephone wires. :)


New Member
I've got parts of my house hooked up to my computer. For the sensors, I used hall-effects (the open collector type that cost less than $2) and put a magnet in the door/window. The digitial signals interface to a PIC microcontroller, which then interfaces to my computer via RS-232. But you can get off-the-shelf digital inputs for you computer (check out http://www.bb-electronics.com/data_acquisition/daq.asp). I use Visual Basic to handle the inputs. The VB app then calls my cell phone through my voice modem (check out Hayes-compatible AT commands).

If you don't want to use your computer, you can build a circuit using a DTMF (dual-tone-multi-frequency) encoder IC to call your cell phone. For the one-minute delay, use a monostable 555 timer. You can use this for 1) setting the alarm and have 1 minute to leave your house, and 2) turning off the alarm before 1 minute when entering your house.

This was a fun project and got me interested in home automation. The next step is to be able to call my computer from my cell phone and have it control things in my house! Hope some of this helps and have fun w/ it!
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