SteveGlover
Programmer
Hi!
Im developing system that comprises a Burglar alarm panel that connects to a standard phone line using a low speed modem. A remote PC (+modem) can phone up the panel for remote diagnostics, programming, etc.
In the UK its common to use the same phone line for both the Burglar alarm panel and fax machine (phone lines are expensive!), so I need a means of defeating the fax machine (stop it answering the call).
The usual way seems to be to put the fax machine on say 5 rings to answer. The PC can dial the phone line and let it ring just once or twice and then hang up. The fax machine won't answer the call (it's on 5 rings), but the Burglar alarm panel recognises the short ring sequence and starts a 60 second timer. The next time that the phone rings within this 60 second window it answers the call immediately and so defeats the fax machine.
In theory this should work, but the problem is that I can't figure out a reliable and robust way ensuring that the PC modem only lets the line ring once or twice before hanging up. I could time it on a typical modem and typical line, but its hardly likely to be reliable across different modems and different phone line providers. The PC could be connected to a mobile phone, which often take a little longer to establish a call.
Has anyone encountered the same problem before? Any ideas on how to determine how many times the "far end" has rung?
Thanks
Im developing system that comprises a Burglar alarm panel that connects to a standard phone line using a low speed modem. A remote PC (+modem) can phone up the panel for remote diagnostics, programming, etc.
In the UK its common to use the same phone line for both the Burglar alarm panel and fax machine (phone lines are expensive!), so I need a means of defeating the fax machine (stop it answering the call).
The usual way seems to be to put the fax machine on say 5 rings to answer. The PC can dial the phone line and let it ring just once or twice and then hang up. The fax machine won't answer the call (it's on 5 rings), but the Burglar alarm panel recognises the short ring sequence and starts a 60 second timer. The next time that the phone rings within this 60 second window it answers the call immediately and so defeats the fax machine.
In theory this should work, but the problem is that I can't figure out a reliable and robust way ensuring that the PC modem only lets the line ring once or twice before hanging up. I could time it on a typical modem and typical line, but its hardly likely to be reliable across different modems and different phone line providers. The PC could be connected to a mobile phone, which often take a little longer to establish a call.
Has anyone encountered the same problem before? Any ideas on how to determine how many times the "far end" has rung?
Thanks