atcomsystems.ca/forum Forums General General Telephone & Systems Information POTS: What placed between tip/ring will simulate "off hook" condition?

TAPS and TOPS were Bell System practices, one for installation and one for trouble shooting.

Jeff - sent you a PM regarding TAP

Captain - even a ring trip caused by a faulty or incorrect protector will squelch the ring cycle. You can simulate this with a 56V/5W Zener diode placed across the line. One direction will short the line totally, the other will do nothing until the ring comes in. 90V will overcome the 56V threshold and it will conduct to stop the ring in its tracks.

The elements in solid state protectors are basically two zeners back-to-back so as to give non-polarized (AC) clamping. So a single zener is going to do the same but will be polarity sensitive as you point out.

In many cases the caller will hear maybe a half ring although you may not hear anything.

If you wanted to allow a full ring (or more) then pick up the line you would have to get a little more complex. A delayed relay powered by the ring voltage that would put a short on the line comes to mind.

-Hal

I'm using an ELK-930 to detect ring, which pulls to ground when the ringing voltage is approx 50 volts. It then triggers a relay (ELK-960) which performs the task that I need (shorts two wires for one full second).

This works great with one exception.

The problem is that the ELK-930 follows the ring pattern. I need one-shot and done (at least for a few minutes) for my task.

Yes, I can hang-up after one ring -- that's what I do now and it works just fine. The ELK-930 triggers immediately, so there is a lot of time to hang-up, but I'd really like a more elegant solution.

I could put second relay in the middle with a delay which would ignore further input from the ring detector for a few minutes, but it sounds like the zener diode might avoid that complexity.

I think I understand what you are saying about how a zener diode works: A zener diode placed between the ring/tip just sits there and does nothing until it gets ringing voltage, higher then its zener rating. It then connects the ring/tip, causing a short which "answers" the phone. With the phone answered, the ringing voltage stops, so the zener stops shorting, thus the phone is "hung-up." Do I have that about right?

So that brings up several questions:

Will the zener diode prevent the ELK-930 from detecting ring?

Is it sound practice to just short the lines, rather than simulate a phone (like with a 1200 ohm resistor which was suggested)?

Any other reason this wouldn't work for my application?

Finally, is there an economical source for a 56V/5W zener diodes? I checked Radio Shack, but nothing close to those specs. Found a 56V/5W online for cheap, but the minimum order and shipping/handling was outrageous.

Really appreciate all the help -- I don't know that much about electronics, just enough to be dangerous and have some fun!

Try DIGI-KEY for the Zener Diode. Trouble is, again, you won't hear much, if any, of the ring.
What will work, and no I don't have a schematic, would be a Full wave bridge, rated at 1 amp and 400 volts or more, with the AC leads across T and R, with a, .47 ufd 200v or more rating, capacitor in series with either T or R. Use the dc output of the bridge to charge a capacitor. Use the charged cap to operate a low current, low voltage relay, with a resistor in series with the relay coil to slow the capacitor discharge, to apply a 600 to 1.2K ohm resistance across T and R. I'm guessing you'd spend about 10-15 bucks max on the parts. Trouble is, without specs for the capacitor, resistor' and relay, you'll spend 3 times that much buying assorted parts to try and get the line short timing where you want it. John C.

Thanks for all the help. I really appreciate it. I believe in closing threads (for future searchers) so here's the outcome.

Never did find a cheap source for a Zener Diode. Individual diodes were dirt cheap, but most places had minimum charges, minimum quantities, etc. I would have liked to try that configuration as it seems the most elegant solution.

Instead, I put a second relay in the circuit so now there are two relays which trigger simultaneously from the ring detection circuit. One does the work I need. The second momentarily shorts across tip/ring with a 1200 ohm resistor, 5 watts, thereby causing the answer/hang up condition I was looking for.

Thanks again for the advice on the 1.2K ohm resistor. Not sure whether the 5 watts was overkill or underkill, but it was what I was able to get through serendipity.