Robust Home-Control System Design for Tamper-Resistant Door Sensor Connections

Hi,My googling hasn't led me to anything worthy, hence time to request help from fellow dabblers.I'm planning on designing a resilient home-control system and would like to steal ideas for how to connect (say)door sensors to a digital circuit. I want the system to be robust, being able to withstand accidentalor malicious mains-electricity encounters. Plus deal with any tampering (short-circuit, open circuit) thata bad person might consider.Anyone got links to sites that cover such requirements? Any pointers gratefully received.Thanks in advance.Mungo Henning

I don't have any links to sites off the top of my head but have a few ideas from my experience in designing robust systems.
Any
signals traveling from one box to another MUST be protected from both
over-voltage and over-current.  A TVS diode (or similar) and series
resistor will probably do the trick although you may want to use an
opto-isolator on one end or both.
For open-circuit/short-circuit,
your best protection is to have some sort of signal protocol between
the parts. for instance, periodically send a series of pulses and get
back a series of pulses and if no response then trigger the alarm.
Something similar to this would also work for wireless devices.

[Got an error last time I replied, so trying again]Hi Elizabeth,Many thanks for taking the time and trouble to reply to me. Here's my follow-on to your comments:1. Opto-isolators are a must at the "delicate" end of the system, so I agree with you there.2. For hostile environments and possibly exposed conductors I'm thinking that A.C. signal source ought to be used so that there's no electrolysis of any switch contacts.3. I'd like a "window" system where the return signal (say) is of a known voltage and thus short-circuiting as well as open-circuiting the connecting wire is detectable at the delicate control-panel end. But how to devise this? Something like four voltages: open-circuit, active low, active high, short circuit.4. I'm trying not to be over-fancy, but it would be nice to build in resilience.5. I dislike wireless devices; much prefer wired. My preference.Further feedback appreciated if possible please.Regards
Mungo

Hi Mungo Henning,Your device should be robust to meet any environmental condition. Fo any kind of application and industrial purpose I would suggest you the following wireless sensors. Wireless Temperature Sensors. These temperature sensors can survive any conditions and long life. Wireless Pressure Sensors. These Sensors provide accurately determines Pressure and meet industrial standards. These Wireless Sensors can be extended to the range of 2 miles and the distance can be enhanced using   LongRange Wireless Gateways. These are made as per industrial standards and totally fits into your requirements.ThankYou

Mungo,Sorry for the delayed response. I only just now noticed your request for further feedback.AC signal source for preventing electrolysis is easily implemented by having a square wave generator at one end (look up 422 or 485 driver for some ideas). If you add some resistors as shown, I think this will implement the window system. If you apply a square wave to the two bias signals, the sense voltage should be between the two bias signals and closer to one or the other depending on the state of the door switch and the resistors you choose. If you have open or short the sense will be equal to one of the bias voltages.
This does not show opto-isolator or other protection circuit in the control box.

Indebted once again to you Elizabeth: thanks for replying.Mungo

I guess I shouldn't feed the trolls, but you didn't really read my requirements, just used the opportunity to market some goods, didn't you? That's not nice. If I want to buy stuff I can search for it, not expect you to promote something you probably would earn money from.Regards
Mungo