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Security Alarm project — Parallax Forums

Security Alarm project

exp1exp1 Posts: 22
edited 2006-09-15 20:34 in BASIC Stamp
Hello people,

I am new to electronics so please be kind turn.gif

I want to make security alarm project for my home and I am thinking of using around 11 PIR sensors (motion control) and some sensors for the doors ( the open-close switch for the doors ).

The idea is that I will connect a GSM module (Noklia N12i) and finally the module will send me an sms message if the alarm is raised. And of course some beels will ring.

My problme that I think that I will have is the following:
I will need several meters of cable in order to place all the sensors. I haven't used wireless because it is more expensive and because I have already purchased the sensors burger.gif

Do you think that the signal will be lost because of the wire's length ?
Will I need something like a repeater to reapet the signal ?

SOme informations would be useful.

Thank you in advance

Comments

  • matthelmmatthelm Posts: 19
    edited 2006-09-14 14:38
    I'm doing something like this, and decided to add a differential driver to the output of each sensor. This adds a bit to cost and power usage, but makes sure that the signal gets where it should be. I was going to use a standard RS-485 driver, and cat5 wire. Both of these are easy to find and use. I was just going to disable the receive on the RS-485 at the sensor.
  • exp1exp1 Posts: 22
    edited 2006-09-14 15:55
    matthelm Thank you for the quick answer.

    But because I am new I would like a bit more help if you want.
    Are u able to give a general diagram of the connections that you have made ?

    From the little that I have read for the rs485 is being used for intranets if I am not wrong.
    Do we know the max length that it can safely send/receive the signal ?

    Is it something like a filter that takes out noise ?

    In addition I am not sure if we have the same name here (europe) for the "cat5" cable.

    Do you use PIR sensors?
  • exp1exp1 Posts: 22
    edited 2006-09-14 16:06
    I think I found an answer to one of my questions

    "With RS485 communication distances of 1200 m are possible."
  • exp1exp1 Posts: 22
    edited 2006-09-14 16:07
    here is the URL:
    http://www.lammertbies.nl/comm/info/RS-485.html
  • exp1exp1 Posts: 22
    edited 2006-09-14 16:32
    Do you think these IC do our job ? How are we going to connect them to the sensor/lines ?
    http://www.national.com/pf/DS/DS3695A.html
  • matthelmmatthelm Posts: 19
    edited 2006-09-14 18:00
    Sorry, I'll be breadborading mine, and know electronics, so don't have a drawing. (Plus I'm not living at home right now, so have no access to hardware/software or even the house!). I will try to talk you thru some of the basics.

    First, that chip looks fine, can't remember which one I'd picked out at Digi-Key. Think it was the cheapest that Digi-Key sells singles of. wink.gif (I did see a free sample if you have a bussiness address!)

    At the sensor end:
    Hook the output of the sensor to pin 4 (DI).
    Tie 3 (DE) and 2 (RE) high (VCC) to enable the transmitter and disable the reciever.
    Hook 6 & 7 (DO and _DO) to the wire.
    Use the spare wires in the cat 5 as power. (I was going to use 7-12 volts and have a regulator on the board too.) Cat 3 might be cheaper, but I have a roll of cat 5 laying around.

    At the stamp end:
    Hook 1 (RO) to the stamp.
    Tie 3 (DE) and 2 (RE) low (GND) to enable the receiver and disable the transmitter.
    Hook 6 & 7 (RI and _RI) to the wire. (I think it's pin 6 to pin 6 and pin 7 to pin 7, see datasheet).

    You also need a RT at the stamp end. The larger the value, the less current you need at the sensor, but the more problems you might have with noise. I was going to play with this, as my wires aren't going to be super long, but can't even guess where to start. (well maybe a 1K to start, long wires would need smaller values, see the datasheet)

    BTW, I was also thinking of expanding my idea to a security system, so once I start, I'll let you know how mine works out. (late this fall at with current plans) Sorry I can't help more, but I can't even program a stamp here. :-(
  • exp1exp1 Posts: 22
    edited 2006-09-15 06:45
    Thank you a lot for your informations.

    I will take one RS485, datasheet, your informations and I will try to see what I will make up with all of them [noparse]:)[/noparse]

    In case you have something new please let me know. I will do the same.

    Regards
    exp1
  • exp1exp1 Posts: 22
    edited 2006-09-15 15:58
    I have found at the Nuts and Volts area at Parallax this column that I think it is relevant

    Column #28: RS-485 Transceiver for Reliable Network Communications
  • matthelmmatthelm Posts: 19
    edited 2006-09-15 20:34
    That should help. Just remember, you are only sending in one direction, not both.
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