Fire Dept Access Key Switch
T Chap
Posts: 4,223
A fire department wants to have a key to access a suite at the top of an elevator to have be able to get into a private residence in case of fire. The door is electronic, and has a keypad/fingerprint panel for the client. The fire dept wants the key access to be easy to find, not disguised or hidden. Access to the penthouse from the elevator is restricted to the guest via FOB. Putting a key switch is easy, using a simple pulldown on a Prop pin, the keyswitch will set the input high when used. As long as the pin is high, the door will stay open, when it goes back low, the door returns to normal operation.
The problem is though, the very remote and unlikely chance of someone seeing the switch and assuming that it could be a simple matter of cutting the drywall, and shorting the wires together to fire the door. One possible solution is to use a multi conductor cable versus a 2 conductor, and require that the ends of the cable be wired in such a manner so that if someone got into the wires, they would not easily figure out what the combination of wires to short together would be. For example, on an 8 conductor CAT5, several pairs would require to be shorted at all times, several would require to be open, and one pair would go to the N.O. switch. Any alternate combination on the dummy wires would disallow the keyswitch logic in the Prop. Tracing out the wires to the switch would rather quickly make sense of the scheme unless the guts were potted.
Since the access is already quite restricted, this is not critical, but it got me thinking of how best to create a secure entry with a simple switch and key. A keyswitch potted into a box with a serial output would be closer to the ideal. Any suggestions?
The problem is though, the very remote and unlikely chance of someone seeing the switch and assuming that it could be a simple matter of cutting the drywall, and shorting the wires together to fire the door. One possible solution is to use a multi conductor cable versus a 2 conductor, and require that the ends of the cable be wired in such a manner so that if someone got into the wires, they would not easily figure out what the combination of wires to short together would be. For example, on an 8 conductor CAT5, several pairs would require to be shorted at all times, several would require to be open, and one pair would go to the N.O. switch. Any alternate combination on the dummy wires would disallow the keyswitch logic in the Prop. Tracing out the wires to the switch would rather quickly make sense of the scheme unless the guts were potted.
Since the access is already quite restricted, this is not critical, but it got me thinking of how best to create a secure entry with a simple switch and key. A keyswitch potted into a box with a serial output would be closer to the ideal. Any suggestions?
Comments
One option is to use CANbus and to have two nodes - one at the elevator control and the other being the user port in the wall board. A multi-wire cable can provide a pair for CANbus communication and other wires can provide power to the unit installed in the wall. LAN cable is a good solution. Communications is RS-485
Why so?
1. Anyone breaking into the node would have to know quite a bit about CANbus to get the other end to activate and would have to come prepared to deal with CANbus.
2. By using non-standard crystals for the bit rate, the CANbus protocol would be unknown to the burglar.
3. CANbus has millions of permutations for code, so just splicing into the wire and using an oscilloscope to get the bit rate is not going to be enough.
4. CANbus is reliable.
5. Codes can be reprogrammed at times on chip sets that can be easily swapped out if the need arises to change code (the chips are DIP packages).
6. CANbus can identify errors, including someone trying to ping the network. This can set off an alarm, used to email a warning, or just retained in a counter that can be monitored by the savy installer.
The thing about the Propeller is that the firmware is on EEPROM and not in any way disguised, but CANbus CPUs have the ability to make decoding firmware very difficult without actually taking the chip apart and looking at how the firmware burned into logic.
I like the Propeller for a lot of applications, but security is not really a strong feature.
Sadly there are always ways to work around security. I suppose a video camera on the unit would assure that any hacker is on record. But one still has to identify and catch the culprit.
Something that needs to be considered... because the situation would be dealing with life or death, it needs to be robust. Any failure in communication protocol could mean death.
Beau's comment is why most would suggest having a device provided by a big corporation rather than a one off DIY device. After all, if something did go wrong and you were sued, could you afford to go through litigation. Law suits in the USA don't have to prove merit to get filed and to go to court.
M0st people would turn to the elevator service company to provide a solution (and probably pay quite a bit).
that way id there IS no fire ect then the tamper will call the police and set off major alarms .
I am of the premis that If you so choose to use more locks then a jail then its your risk that in a Fire you may Die or what not ..
non of this for a residence should be ""required "".
( not a Huge fan of the NEC or how it is put in to effect )