Alarm Contact

[Luciano]

Hi,

Darrel's schematic:

The components R1 and S1 are grouped into a dotted-line box,
corresponding to a physical unit. (R1 is inside an enclosure with S1).

* * *

It dosen't matter on which contact of the switch S1 the resistor R1 is soldered.

The system is secure only if the switch S1 and the resistor R1 are
in the same enclosure and coated with resin. (One physical unit).

If you put more than one switch in series on the same line, the system won't be secure.

Not secure system

+5 --R2--┐
         |
AN0 -----┴-----------S1--------S2-------S3---------S4R1--┐ 
                                                         |                                                 
GND -----------------------------------------------------┘ 


Secure system

+5 --R2--┐
         |
AN0 -----┴-----------------------------------------S1R1--┐ 
                                                         |                                                 
GND -----------------------------------------------------┘

(R2 is inside the microcontroller enclosure).

Best regards,

Luciano

[Pesticida]

Thanks to all for the answers,but what command I now need to measure this Voltage I have a PIC16F870 with 20Mhz .
What happend when i have a wire ~ 100-300 Meter long.
I dont know how sensitive is a PIC controller.

Thanks a lot People!!!

Bye Pesti.

[Pesticida]

I think that I can use the Alarm circuit like on my draw !?

I have three States,Cicuit :
Magnetic Contact is closed: No Alarm (5K6 Ohm)
Magnetic Contact is Open: Alarm (6K4 Ohm)
Cable Tamper or Alarm Box Tamper is open : Sabotage
ShortCircuit on the loop : Sabotage


The Contacts are inside a door and on the Security side Zone.
I think so is ok or ?
Bye Pesti.

[Darrel Taylor]

Well, I don't have 30 years experience at anything, except "Beer Processor".   I just pour it in one end, and it comes out the other in about a half an hour.   So, maybe I'm not the guy to listen too....but...


It seems to me that most alarm systems are contained within the same perimeter that it is protecting. While the movies always seem to have a key element of the system located in an unsecured area where it can easily be defeated by cutting a couple wires and using some alligator clips.   That's not very realistic.

If any tampering is going to be done to the system, you would first have to breach the perimeter to get to the wiring in the first place. Which of course would set off the alarm.

So, the time when the tampering occurs, is when then system is dis-armed, and people are walking around everywhere unchecked. If you can by-pass sensors during the day, you can come back at night and clean the place out.

In the case of alarmbox.BMP in post #9, all you need to do is twist the two pairs of wires together, and your done.

And, in Luciano's example, you can just bypass any switch with a short, and you're in.

Not secure system

+5 --R2--+
         |
AN0 -----------------S1--------S2-------S3---------S4R1--+ 
                    |__|      |__|     |__|              |                                                 
GND -----------------------------------------------------+

Personaly, I think you are better off using the original plan.

And, you would use the ADCIN statement to read the input. I think that's what you're prior question was??

[Melanie]

Most alarm systems I've come across have a series Resistor in each Sensor. Attempt to bypass the Sensor (with Darrels aligator clips) and you unbalance the circuit setting the Alarm off. But hey, who am I to comment... I'm not thirty yet!

[Pesticida]

Ok thanks people,now I know what i have to do.
I made a Security Software in Visual Basic,for the moment for 4 Alarm Contact.
I have work two week on this Software,the most lost time was on the PIC
controller.

Thanks !!!
Bye Pesti

[Normnet]

I think this was from Forrest Mims. Intelligent Alarm.

Alarm resisters of different values in series.
Each window/door if opened closes across a resistor?
Total resistance (Pic AD) indicates which resistor is shorted.
Even with combinations of resisters shorted it can be determined which windows are opened.
Tamper is if not one of the combinations.

Norm