lairdb@crash.cts.com (Laird P. Broadfield) (03/14/91)
Can somebody point me toward a ring-detection IC? I've checked my recent Harris, Dallas, and SS databooks, and I find lots of Call Progress Detectors, but what I want is ring-detection. Preferably for more that one line per package (I'm thinking 10-20 lines into the device, maybe even 25 and hook up directly to a 21X termination.) Thanks! (P.S. Do the ICLID ICs coming out these days have a ring indication line, or do they assume you've got a separate ring-detect circuit?)
mcmahan@netcom.com (Dave Mc Mahan) (03/18/91)
In a previous article, lairdb@crash.cts.com (Laird P. Broadfield) writes: > Can somebody point me toward a ring-detection IC? I've checked my > recent Harris, Dallas, and SS databooks, and I find lots of Call > Progress Detectors, but what I want is ring-detection. Preferably for > more that one line per package (I'm thinking 10-20 lines into the > device, maybe even 25 and hook up directly to a 21X termination.) Most of the ring detectors I have seen implement this function with an opto-isolated circuit. Basically, there is a large resistor in series with the LED side of the optoisolator placed across the phone line. The resistor is chosen to bleed minimal current from the line during normal on-hook operation and while a voice is connected. The value I recall seeing is on the order of 40K or 50K ohms, but check with me and I'll verify that. I also seem to recall a DC blocking capacitor somewhere in there, but it has been a while (actually two days, but it's been a TOUGH weekend!! :-) since I looked at these things. I have a couple of data books that contain example circuits with these shown. The output of the opto-isolator is fed into a CPU that get interrupted on every ring pulse and sets a flag saying that a ring is occuring. When it stops receiving the pulses after it gets them, it clears the flag. You could do the same thing in pure hardware using a retriggerable one- shot. If you want more info on various sources of example circuits, e-mail me and I'll send you names of data books. Dave McMahan mcmahan@netcom.com {apple,amdahl,claris}!netcom!mcmahan