ron@minnow.sp.unisys.com (Ron Burns) (03/25/89)
I have got a small microcomputer board running my home weather station, and I would like to use one of the serial lines to go to a modem so I can periodically dial up my computer here at work and transfer current weather data. This does not present a problem, except that when someone is home, I want to be able to sense whether the phone is off the hook at another extension so as not to slam an earful of phone dialling tones into someone's ear. This in itself is enough, I guess, but it would be great if the circuit was phone line powered, so that I could put a copy of this circuit on the other extension, so an LED would go on, indicating that the computer was on the phone, wait a moment for it to hang up. the requirements seem simple: 1) TTL compatible output indicating phone off hook at extension or local phone jack. 2) No interference with normal phone operation. 3) (optional) Phone line powered to allow use at other extension. Can someone out there help me with this?? Telephone circuits are just a mystery to me, even though this seems fairly simple. Thanks a lot!! -Ron -- Ron Burns Unisys Corporation UUCP: ...!amdahl!ems!minnow!ron Phone:(612)635-6927 CSNET: ron@minnow.SP.Unisys.Com
clements@bbn.com (Bob Clements) (03/28/89)
In article <1315@minnow.sp.unisys.com> ron@minnow.UUCP (Ron Burns) writes: >... I want >to be able to sense whether the phone is off the hook at another extension >so as not to slam an earful of phone dialling tones into someone's ear. > ... >the requirements seem simple: > 1) TTL compatible output indicating phone off hook at extension > or local phone jack. > 2) No interference with normal phone operation. > 3) (optional) Phone line powered to allow use at other extension. > >Can someone out there help me with this?? Telephone circuits are just a >mystery to me, even though this seems fairly simple. I recently bought an amazingly cheap gizmo for this sort of thing. I've never seen it for sale anywhere else. It is in the Fordham-Scope catalog. (I don't have the number/address here at work. NY area, with an 800 number, I think.) It's a model MS-2 "Message Stopper", price $7.95 (I think, maybe 8.95). It looks like a two-for-one modular jack. One nose that goes into the wall socket, two sockets for two cords. There are two LEDs for activity on the two sockets. One socket is just a copy of the input. The other socket gets cut off if anyone else is using the line. So it can be used for answering machines that don't automatically drop off when the line gets picked up elsewhere. Or for the Watson board, which doesn't drop off either. You could do what you want by having the PC try to make the call, but fail, because it isn't connected to the line when someone's on it. No TTL output, sorry. Meets your items 2 and 3, though. Maybe you could rig a sensor on the LEDs if you really need it, but that would need isolation and all that. Maybe a photocell looking at the LED. Note: When I first saw the ad, I assumed it just had a relay in it that sensed current through one jack and cut off the other. Not so! It really does sense voltage, so it cuts off when any other phone on the line is off-hook. So why doesn't anyone else sell this little gem? > >Thanks a lot!! >-Ron >-- >Ron Burns >Unisys Corporation UUCP: ...!amdahl!ems!minnow!ron >Phone:(612)635-6927 CSNET: ron@minnow.SP.Unisys.Com /Rcc clements@bbn.com