lairdkb@mentor.cc.purdue.edu (Kyler Laird) (10/10/90)
1) I appreciate the response for the DTMF decoder request - especially the ring signal suppressor! 2) Any ideas on _creating_ a ring signal? I'm trying to route an incoming call to a device. I've found out that a 'standard' ring is 48vdc @ 20Hz. How close to this must I get? It would be great if I could use 60Hz, but I doubt that's a good option. (I have little knowledge of analog electronics. Alas, another CS major trying to do EE...) Thanks! --kyler
whinery@hale.ifa.hawaii.edu (Alan Whinery) (10/10/90)
In article <14913@mentor.cc.purdue.edu> lairdkb@mentor.cc.purdue.edu (Kyler Laird) writes: >2) Any ideas on _creating_ a ring signal? I'm trying to route an incoming >call to a device. I've found out that a 'standard' ring is 48vdc @ 20Hz. >--kyler ccording to "Understanding Telephone Electronics" which I bought at Radio Shack in Tippecanoe Mall some years back, the correct ringing signal on a spec FCC telephone set (ha ha ha, find one) is 90 VRMS @ 20 hz. I think the 48 volts you mentioned is probably the "battery" DC line voltage that appears when the line is at high impedance (off-hook). The ring signal in West Lafayette is a pulsed one, meaning that it contains little bursts of the 20 hz during a ring, rather than a constant 20 hz. To emulate this? Your ringer would probably eat 60 hz, but you'd have to knock down the voltage a little, and it would sound funny. The likelihood that there is a high Q 20 hz filter in a phone is relatively slim. It would be cool if you had an autotransformer, with which you could vary the AC voltage from a line socket to experiment. Alan Whinery whinery@hale.ifa.hawaii.edu BSET Purdue 1984
wb8foz@mthvax.cs.miami.edu (David Lesher) (10/10/90)
I'm not clear if the original poster wanted to trip the ring detect in his key system, or generate ring signal to run the phones themselves. In the first case, 60 hz will trip a 1A2 KTU 400 card with no problem. I do recommend an isolation transformer -- about 70 volts RMS should do the job. BUT, 60hz will not run any mechanical ringer I have seen. The normal untuned ones will function on 30hz, however, and most of the simpler KTU supplies actually make that. You have several choices: Try phones with tweedle-deedle ringers. Note that some of those ringer chips are designed with 60hz rejection to avoid false ringing.... Use DC buzzers in the phones, and forget the ringers. Make some 20/30 hz. You may be able to find a supply with this feature at a hamfest. The WECO 113A, 117A&B, and the 20 and 30 series supplies all have ringer voltage supplies. Lorain Products Corp. made thousands of "Sub-Cycle" supplies of various styles and sizes. Making your own supply is not impossible, but is likely non-cost_effective. Exotic magnetics are needed to copy LPC's methods. You could likely build a 30hz oscillator, and follow it with power amps, but again that would be $$$. -- A host is a host from coast to coast.....wb8foz@mthvax.cs.miami.edu & no one will talk to a host that's close............(305) 255-RTFM Unless the host (that isn't close)......................pob 570-335 is busy, hung or dead....................................33257-0335
tomb@hplsla.HP.COM (Tom Bruhns) (10/10/90)
>2) Any ideas on _creating_ a ring signal? I'm trying to route an incoming
Look in the latest (Oct? Nov?) Radio-Electronics magazine. It has an
article on a phone call screening device that among other things generates
a ring signal, and does it fairly cheaply.henry@zoo.toronto.edu (Henry Spencer) (10/10/90)
In article <9770@uhccux.uhcc.Hawaii.Edu> whinery@hale.ifa.hawaii.edu (Alan Whinery) writes: >To emulate this? Your ringer would probably eat 60 hz, but you'd have to >knock down the voltage a little, and it would sound funny. The likelihood >that there is a high Q 20 hz filter in a phone is relatively slim. .. Unfortunately, there is: "classic" phones have mechanically-resonant ringers that really do want something fairly close to specs. (What, you were expecting an *electronic* filter? Don't be silly. :-)) What the cheap electronic phones will take is another question. -- Imagine life with OS/360 the standard | Henry Spencer at U of Toronto Zoology operating system. Now think about X. | henry@zoo.toronto.edu utzoo!henry
roy@phri.nyu.edu (Roy Smith) (10/11/90)
> the correct ringing signal on a spec FCC telephone set (ha ha ha, find > one) is 90 VRMS @ 20 hz. How about the following to generate a fairly ugly 90 VRMS @ 20 Hz signal? First, step 115 VRMS @ 60 Hz (i.e. mains power) down to 90V, and full wave rectify it. Generate a 60 Hz TTL square wave train by any one of a number of methods involving some combination of zener diodes, and schmidt trigger comparators. Run this into a divide-by-3 (2 flip-flops, plus a couple of gates). Use the 20 Hz TTL output of the divide-by-3 to drive a solid-state DPDT relay (basically 4 big CMOS analog switches), cross connected to reverse the polarity of the 90 VRMS, 60 Hz full wave rectified waveform generated in step 1. The output should look like: * * * * * * * * * * * * * * * * * * * * * * * * * * ---*-----*-----*-----*-----*-----*-----*-----*-----*-----*-----*-----*----*--- * * * * * * * * * * * * * * * * * * * * * * * * * * As an alternative, you could use the 1940's technology, brute-force, electro-mechanical way. Use the 115V 60 Hz mains to drive an N-pole synchronous motor. Couple the shaft to a 3N-pole 90V synchronous generator (maybe even on the same shaft in the same case) and out comes your 90 VRMS 20 Hz ringing signal, probably with an efficiency approaching 90%. Why do I have the feeling that if I go down to the centrex room in our building, I might actually find something like this? -- Roy Smith, Public Health Research Institute 455 First Avenue, New York, NY 10016 roy@alanine.phri.nyu.edu -OR- {att,cmcl2,rutgers,hombre}!phri!roy "Arcane? Did you say arcane? It wouldn't be Unix if it wasn't arcane!"
gsteckel@vergil.East.Sun.COM (Geoff Steckel - Sun BOS Software) (10/12/90)
It's fairly easy (:-) to generate quasi-sort-of-sine-looking-things at more-or-less 60-80VAC 20HZ by taking a filament transformer (remember them?) and running it backwards, resonating the primary with a large NONpolarized capaicitor, and using robust transistors (2n3055 or power FETs) in a multivibrator configuration. Using feedback from the resonant load eliminates needing to tune a separate oscillator. I'd recommend a 300 mA 12VCT filament transformer driven off 5 volts. Use an L/C/R bridge and 1/2pi sqrt(L * C) to determine the C value (don't be surprised if it's several hundred microfarads or larger!), or just play around with a scope. This can generate a LARGE jolt on its output, and remarkably large reflected voltages on the driver transistors. Be careful & have fun! regards, geoff steckel (gwes@wjh12.harvard.EDU) (...!husc6!wjh12!omnivore!gws) Disclaimer: I am not affiliated with Sun Microsystems, despite the From: line. This posting is entirely the author's responsibility.
roy@phri.nyu.edu (Roy Smith) (10/12/90)
I wrote: > Use the 115V 60 Hz mains to drive an N-pole synchronous motor. Couple the > shaft to a 3N-pole 90V synchronous generator [...] and out comes [...] 20 Hz Aaarrrggghghg! That'll produce 180 Hz. What I meant to say (honest :-)) was use a 3N-pole motor driving an N-pole generator. So, how come nobody flamed me for my error yet? -- Roy Smith, Public Health Research Institute 455 First Avenue, New York, NY 10016 roy@alanine.phri.nyu.edu -OR- {att,cmcl2,rutgers,hombre}!phri!roy "Arcane? Did you say arcane? It wouldn't be Unix if it wasn't arcane!"
grayt@spock (Tom Gray) (10/12/90)
In article <2876@jaytee.East.Sun.COM> gsteckel@east.sun.com (Geoff Steckel - Sun BOS Software) writes: >It's fairly easy (:-) to generate quasi-sort-of-sine-looking-things at >more-or-less 60-80VAC 20HZ by taking a filament transformer (remember them?) In this discussion, one must remeber that the object of the ringing signal is to alert the user. When he is alerted he will take the telephone off hook and the telephone system (in this case the KSU) must detect this transition. The 20Hz ringing signal must be a very clean sine wave for this to happen releiably. Any imperfections in the sine wave will make the task more difficult. If not done correctly the dreadded result of PRE-TRIP will happen. In this case, the system will see transiensts from the ringing signal and falsely decide that the telephone is off hook. Remembet that the ringing generator is driving up to 5 telephones with a variety of ringing devices from electronic to mechanical. The impedance of this configuration can range from 50K to 1.2K or 800 ohms. The ringing detector and ringing generator must operate reliably into all of these loads. Although telephone ringing sounds trivial - it is not a trivial task to make it operate reliably - with all types of telephones into all types of loops.
wb8foz@mthvax.cs.miami.edu (David Lesher) (10/13/90)
In <4838@smithd> grayt@spock (Tom Gray) writes: >In this discussion, one must remeber that the object of the ringing signal >is to alert the user. When he is alerted he will take the telephone off hook >and the telephone system (in this case the KSU) must detect this transition. >The 20Hz ringing signal must be a very clean sine wave for this to happen >releiably. Any imperfections in the sine wave will make the task more >difficult. I'm getting a little confused here. I can think of NO way a 1A2 KTU could be bothered by crummy 20 hz. (We were talking old WECO key systems, weren't we?) 1) The local {2,3}0 hz goes out on the CA (Common Audible) line, switched by the 400 {B,D,G,H} card and the motor-driven interupter. At no point is it across T&R as the CO ringing is. 2) The card trips (stops ringing) on the basis of A_control current, run by a mechanical hookswitch contact in each set. 3) The 400 card on each line also looks at loop current (mostly for the HOLD function) but that too is switched by a mechanical hookswitch. I've rung phones with really crappy stuff. I've also overloaded small Sub-Cycle type supplies with too many ringers so they would 'dink' one each cycle, before stalling. One advantage of the 1A2 is it is too dumb to be confused by anything short of lightning. For more details, see 325-010: Bell System "Key Systems Service Manual, vol 1 and 2." -- A host is a host from coast to coast.....wb8foz@mthvax.cs.miami.edu & no one will talk to a host that's close............(305) 255-RTFM Unless the host (that isn't close)......................pob 570-335 is busy, hung or dead....................................33257-0335
gaarder@batcomputer.tn.cornell.edu (Steve Gaarder) (10/18/90)
Last time I checked, Fair Radio Sales has a ring signal generator in their catalog. It takes a 90 volt DC input and makes 90V 20 Hz. It is basically a vibrator (anyone remember those?) unit. I bought one; it does work, though I haven't built it into anything yet. Steve Gaarder gaarder@bat.tn.cornell.edu