waters@KARNAC.DEC (Lester Waters PCSG) (12/17/85)
I have a multiline phone with my Bell 212 modem. There is only one 2-wire input to the phone for line 1. After fooling with the phone for a while, I managed to hook up line 2, so now I can select either line 1 or line 2. Unfortunately, this phone is a little different since it hooks into the Bell 212. The phone does not ring when a call comes in on line 2 (but I can answer it if I hear the other phone on that line ring). Also, the red HOLD button does not work for either line. Does anyone know how I might: (a) Get the red HOLD button to work properly (if anyone out there has a real familiarity with multiline Bell phones) - or - (b) build an external circuit which I can use to place one line on 'hold' and direct the other line into the phone. (Radio Shack sells something like this for $50 -- what's inside it?) Lester Waters Waters%VIKING.DEC@DECWRL (ARPA) ...!decvax!decwrl!dec-rhea!dec-viking!waters (UUCP)
telecom@ucbvax.UUCP (12/25/85)
> I have a multiline phone with my Bell 212 modem. There is only > one 2-wire input to the phone for line 1. After fooling with the > phone for a while, I managed to hook up line 2, so now I can select > either line 1 or line 2. Unfortunately, this phone is a little different > since it hooks into the Bell 212. The phone does not ring when a call > comes in on line 2 (but I can answer it if I hear the other phone on that > line ring). Also, the red HOLD button does not work for either line. > Does anyone know how I might: > > (a) Get the red HOLD button to work properly (if anyone out > there has a real familiarity with multiline Bell phones) > > (b) build an external circuit which I can use to place one > line on 'hold' and direct the other line into the phone. > (Radio Shack sells something like this for $50 -- what's > inside it?) A multiline telephone (564 or 565 type) used with an individually mounted data set was never really intended to pick up other than the data line itself. The multiline telephone was simply a convenient and less expensive method for data/voice use on ONE LINE than the original `data auxiliary set' concept. A multiline telephone needs 1A, 1A1, or 1A2 key telephone apparatus to support the line hold, illumination, and common audible ringing functions. I don't believe it is feasible to attempt to mix a multiline telephone set used on a data set WITH key equipment to pick up other lines. I would suggest that you buy an off-the-shelf two-line telephone with hold function. If you are determined to build you own hold function (we won't talk about Part 68 :-) ), you can take two approaches: 1. Use a 300 ohm 2 watt resistor in series with a switch; this goes across tip and ring of the telephone line - the line is "on hold" when the switch is operated. This approach has the disadvantage of not releasing automatically if the distant party goes on hook. 2. Use a circuit with an SCR. This is rather difficult to draw over Usenet, but in general the circuit should have a full wave bridge rectifier of 1A @ 200 WVDC (minimum) connected with the AC leads across tip and ring. The + rectifier lead goes to a 100 ohm 2 watt resistor which in turn goes to the anode of an SCR (1.0 ampere @ 200 PRV min). The cathode of the SCR returns to the - lead of the rectifier. Connect a 1,000 ohm 1/2 watt resistor between the gate of the SCR and the cathode of the SCR; connect a 0.1 uF @ 100 WVDC capacitor across this resistor. Connect a normally-open momentary push switch between the gate of the SCR and the anode of the SCR. Operating the push switch will put the line on hold. Connect a second normally-open momentary push switch directly across tip and ring; operating this second switch will release the hold. This circuit will release the hold upon a momentary central office loop open which should accompany a distant party going on hook. A status indicator can be provided by connecting an LED in series with a 150 ohm ohm 1/2 watt resistor across the above 100 ohm series resistor; the anode of the LED goes toward the + lead of the rectifier. I have not specified a gate current for the SCR since a wide variety of SCR's will function in this simple application; the 1,000 ohm resistor and 0.1 uF capacitor above should serve to prevent a false hold trigger during dial pulsing or ringing. It is possible to have a circuit which will automatically release the hold when the telephone is picked up again - instead of using the second release push switch. This is a little trickier to do; one way is to detect a voltage decrease across the 100 ohm resistor (which corresponds to picking up a telephone) and discharge a capacitor across the SCR, thereby turning it off. I will leave the details to you as a design challenge. One hint: you will probably not find it reliable to assume that the parallel DC resistance of picking up the telephone set will sufficiently reduce the current through the SCR to cause it to cease conduction - a more `active' measure is required. ==> Larry Lippman @ Recognition Research Corp., Clarence, New York <== ==> UUCP {decvax|dual|rocksanne|rocksvax|watmath}!sunybcs!kitty!larry <== ==> VOICE 716/741-9185 {rice|shell}!baylor!/ <== ==> FAX 716/741-9635 {G1, G2, G3 modes} duke!ethos!/ <== ==> burl!gladys!/ <== ==> "Have you hugged your cat today?" ihnp4!/ <==