deanr@sco.COM (Dean Reece) (02/20/90)
In article <1629@ariel.unm.edu> ee5391aa@hydra.unm.edu.UUCP (Duke McMullan n5gax) writes: >A real, live, appropriately technocratic solution to this did occur to me.... > >Build a little black box which detects the ringing voltage (the phone may ring >... Well, it sounds like the original poster wanted an undetectable box (small, un-obtrusive, and low/no power consuming - cheap would be nice too!). So my idea is simply build a passive notch filter and place it in series with the red/green (tip/ring) wires at the tele main connection. The ringing is (as another poster mentioned) about 30 hz and around 100 Volts. Well, dropping this to around 10-30 volts might just keep the ringer from going. That depends largly on the ringer equivalences of all the phones on the line, the condition of the wires in the house, the temperature/humidity outside (yes phone voltages vary with the weather). You MUST pass the DC component, otherwise the phones will not be able to dial out; and you MUST pass everything over about 100 hz to get the voice and in-band signaling to go through. A notch filter set between 10 and 100 hz with about 12 db loss at 30 hz would be ideal. I'm not an EE, so the design is left as an excercise to the reader. One other option would be to fake a PBX. I'll try to keep my ramblings coherent here. 1st, have a relay that disconnects the in-house phone lines from the telco lines and connect them (the in-house lines) to a voltage source run through about a 600 ohm resister. Moniter the voltage on the in house lines. While the phones are on-hook, the voltage will be about what the voltage in the DC supply is. When sombody takes a phone off-hook, the voltage will drop to about 1/2 the DC voltage (if more the 1 phone go off-hook together, the voltage will be even lower). So set up a comparator with one input connected to a 75% volage divider off the DC supply, and the other input directly off the in house lines. When the in house lines drop below the 75% threshold, the comparater will fire, and you flip the relay. Now the phone is connected to the telco lines, they will detect the off-hook condition and produce a dial-tone. You continue to moniter the voltages. When they return to normal for on-hook telco lines (about 60vdc - or anything over about 12vdc) you flip the relay back to the fake PBX, looking for another off hook condition. When an outside caller tries to ring the number, the signal never makes it to the phones, since the relay has the telco lines isolated from the in-house lines. If sombody takes a phone off-hook at the same time as sombody is calling in, it will look to all teh equipment as if a normal answer had happened. The net effect is the same as removing the ringer from all the phones, except that no modification of equipment in needed. Hope it helps ______________________________________________________________________ | Dean Reece Member Technical Staff |"The flames are all long gone | | The Santa Cruz Operation 408/458-1422 | but the pain lingers on" | |___________deanr@sco.com_______________|___________________Pink_Floyd_|
heath@shumv1.uucp (Heath Roberts) (02/22/90)
>> My understanding is that the ringing signal the called party gets and the >> ringback (calling party hearing the ringing) are unsynchronized. Now, I >> _believe_ this might happen : your ring generator starts out in the quiet >> portion of its ringing cycle, but the caller hears a full ring before your >> circuit gets its ring, picks up the phone and puts a busy tone on it. > >This is correct. Unless the caller and person called are terminals on the >same exchange, the ring tone generated by the two exchanges (the exchange of >the calling party and the exchange of the called party) are indeed >unsynchonised and hence the above scenario can happen. > Doesn't matter if you're on the same exchange or not. I've been working on a switch , called a phone from another phone on the next _line card_ (they're about an inch apart) and they're not synchronized. There are enough sync problems in a switch without worrying if you get ring and ringback at the same time. It's not necessary and they're totally different signals--why bother? Heath Roberts NCSU Computer and Technologies Theme Program heath@shumv1.ncsu.edu