philb@orca.UUCP (Phil Biehl) (03/18/86)
I'm in the process of adding telephone capabilities (autopatch) to the UHF ham repeater I am working on. I would like to be able to detect the ringing current produced by an incoming call. What I need is a CMOS compatible signal indicating that ringing current is present on the drop. That is, a pulse for every ring burst. I would like to have as much isolation from the drop as possible and have been considering optoisolators to connect the logic to the line. I would like to get a consensus on your favortie ring current detector. Please mail or post responses. Thanks much. Phil Biehl (503) 685-2122 Tektronix Inc., Wilsonville OR tektronix!orca!philb
kludge@gitpyr.UUCP (Scott Dorsey) (03/21/86)
In article <2032@orca.UUCP> philb@orca.UUCP (Phil Biehl) writes: > > I'm in the process of adding telephone capabilities (autopatch) > to the UHF ham repeater I am working on. I would like to be > able to detect the ringing current produced by an incoming > call. What I need is a CMOS compatible signal indicating that > ringing current is present on the drop. That is, a pulse for > every ring burst. My suggestion is one of the neon optoisolators on the market. Just hook one end to the phone line and the other one to a 741 op amp. Or, taping an NE-2 bulb to a CDS cell will probably work, although I wouldn't bet on reliability. I know that HP makes some neon optoisolators, but you can probably get them cheaper... -- ------- Disclaimer: Everything I say is probably a trademark of someone. But don't worry, I probably don't know what I'm talking about. Scott Dorsey " If value corrupts kaptain_kludge then absolute value corrupts absolutely" ICS Programming Lab (Where old terminals go to die), Rich 110, Georgia Institute of Technology, Box 36681, Atlanta, Georgia 30332 ...!{akgua,allegra,amd,hplabs,ihnp4,seismo,ut-ngp}!gatech!gitpyr!kludge
larry@kitty.UUCP (Larry Lippman) (03/22/86)
In article <2032@orca.UUCP>, philb@orca.UUCP (Phil Biehl) writes: > I'm in the process of adding telephone capabilities (autopatch) > to the UHF ham repeater I am working on. I would like to be > able to detect the ringing current produced by an incoming > call. What I need is a CMOS compatible signal indicating that > ringing current is present on the drop. That is, a pulse for > every ring burst. > I would like to have as much isolation from the drop as possible > and have been considering optoisolators to connect the logic to > the line. A simple ring detector can be made from a GE H11AA1 optoisolator, which is a dual LED device which detects AC. Connect the LED input in series with a 3.9 K resistor and a 0.68 uF capacitor, and then across tip and ring of the telephone line. The optoisolator output is a transistor; overall sensitivity can be varied by using a resistor between the base and emitter. Some integration should also be done to minimize dialing transients from being detected; this can be done with a capacitor across the base and emitter. For CMOS use, the emitter can be at Vss to sink a logic input using the collector. ==> Larry Lippman @ Recognition Research Corp., Clarence, New York <== ==> UUCP {decvax|dual|rocksanne|rocksvax|watmath}!sunybcs!kitty!larry <== ==> VOICE 716/688-1231 {rice|shell}!baylor!/ <== ==> FAX 716/741-9635 {G1, G2, G3 modes} duke!ethos!/ <== ==> seismo!/ <== ==> "Have you hugged your cat today?" ihnp4!/ <==