Silver,
Apologises for the pause in service, was off in Paris for the week...
Burglar alarm systems normally work using a one or more simple serial wire circuits that operate in a daisy-chain though each sensor and around the target area. This area may be broken down into zones typically a 24 hour always on tamper zone, an entry route/zone, an exit route/zone and one or more everywhere else zone(s).
The sensors used on doors and widows (usually) have four connections but basically just two wires routed through them. One wire, a simple loop though is the tamper circuit the second wire is through the sensor's reed switch or relay contacts. When positioned with the door or window closed the matching magnet will be holding the reed switch contacts closed. You will have two continuous current paths, energised by (say) 12 volts (5 or 3.3volts) and including a current limiting resistor that can be used to keep the opto-LED illuminated (and not stressing it) thereby confirming all reed switches are being held closed by their adjacent magnets and the tamper circuit is complete, both passing current around the zone loop.
The PIRs are in essence the same as the simple reed switch/magnet door and widow sensors except they use a relay whose contacts open when the PIR sensor spots something. The PIR relay contact can be wired in series with any other PIR or simple reed sensor and should also honour the tamper circuit loop-though. Note that the sensing circuit is passive, there's no voltages to measure just either zero ohms, its connected or open circuit - infinity.
The PIRs also need power, typically 12volts so that'll be one more pair of wires within the standard cabling you will be using.
Your burglar alarm will likely be mains powered but should include options to continue operation during a mains power failure. Generally the power backup is 12volt lead acid battery, most likely a gel or sealed type. It will need a charging system, usually a trickle charge, of some type.
Twelve volt lead acid batteries, under charge, run nearer 13.5volts meaning anything running off the backup system must tolerate whatever higher voltage exists. For simplicity, most burglar alarms run directly off the ~13.5 volt lead acid battery. Typically, PIR sensors need somewhere around 12volts to work but will tolerate a bit less or a bit more, i.e. your 13.7volts.
Would suggest a Pico or better still a Pico-W would be a better, cheaper controller and more tolerant of being turned on and off. It doesn't need to boot up or an ordered shutdown. Using the Pico-W brings with it the option of a simple browser interface accessible via a smart phone from anywhere in range. However, the Pi being a fully functional computer also brings you a WiFi control interface plus email alerts via any number of command line email clients available.
The sky isn't the limit on this.
Apologises for the pause in service, was off in Paris for the week...
Burglar alarm systems normally work using a one or more simple serial wire circuits that operate in a daisy-chain though each sensor and around the target area. This area may be broken down into zones typically a 24 hour always on tamper zone, an entry route/zone, an exit route/zone and one or more everywhere else zone(s).
The sensors used on doors and widows (usually) have four connections but basically just two wires routed through them. One wire, a simple loop though is the tamper circuit the second wire is through the sensor's reed switch or relay contacts. When positioned with the door or window closed the matching magnet will be holding the reed switch contacts closed. You will have two continuous current paths, energised by (say) 12 volts (5 or 3.3volts) and including a current limiting resistor that can be used to keep the opto-LED illuminated (and not stressing it) thereby confirming all reed switches are being held closed by their adjacent magnets and the tamper circuit is complete, both passing current around the zone loop.
The PIRs are in essence the same as the simple reed switch/magnet door and widow sensors except they use a relay whose contacts open when the PIR sensor spots something. The PIR relay contact can be wired in series with any other PIR or simple reed sensor and should also honour the tamper circuit loop-though. Note that the sensing circuit is passive, there's no voltages to measure just either zero ohms, its connected or open circuit - infinity.
The PIRs also need power, typically 12volts so that'll be one more pair of wires within the standard cabling you will be using.
Your burglar alarm will likely be mains powered but should include options to continue operation during a mains power failure. Generally the power backup is 12volt lead acid battery, most likely a gel or sealed type. It will need a charging system, usually a trickle charge, of some type.
Twelve volt lead acid batteries, under charge, run nearer 13.5volts meaning anything running off the backup system must tolerate whatever higher voltage exists. For simplicity, most burglar alarms run directly off the ~13.5 volt lead acid battery. Typically, PIR sensors need somewhere around 12volts to work but will tolerate a bit less or a bit more, i.e. your 13.7volts.
Would suggest a Pico or better still a Pico-W would be a better, cheaper controller and more tolerant of being turned on and off. It doesn't need to boot up or an ordered shutdown. Using the Pico-W brings with it the option of a simple browser interface accessible via a smart phone from anywhere in range. However, the Pi being a fully functional computer also brings you a WiFi control interface plus email alerts via any number of command line email clients available.
The sky isn't the limit on this.
Statistics: Posted by RaspISteve — Sat Jul 06, 2024 2:54 pm