I hope I am using the proper term "Inductive pickup". I am using the below Contactless Ring Detector Circuit to detect votage present on a phone line. My board is designed after the below circuit but, does not use Q3, S1, or K1 Piezo Buzzer. The trick I found was to wrap an "insulated wire" (5 wraps) around the RED (RING) wire of the phone line and the circuit will detect when a 90VAC (DC Drops to -20VDC) when call happens.
I also found out that by using an uninsulated alligator clip over both Telephone Lines I could pick up the "ON HOOK" -48VDC as well.
So my quest is to use (when present) the -48VDC "ON HOOK" to keep a relay OPEN and to use the 90VAC to cause the relay to Close.
By your schematic it appeared I just needed a capacitor to stop the DC and inductively pickup the 90VAC down stream from the capacitor.
L1 of Q1 is the inductive wire wrap (If I am saying that propertly)
Again, thanks for your help.
(SEE Below image for Notes provided with circuit below)
The contact less telephone ringer circuit can produce a ring as well as a visual indication when a call comes.The main advantage is that since there is no direct contact between the phone line and the circuit there is no chance for a loading or disturbance in the telephone line.
When the telephone rings 60 Hz AC signal is generated which produces a proportional magnetic field around the telephone lines.These magnetic field will be picked up by the coil L1 due to electromagnetic induction.A proportional voltage is developed across L1 and it will bias transistor Q1 to ON.This results in the conduction of transistors Q2,Q3 andQ4.The buzzer will ring and the LED will glow.The switch S1 acts as an ON/OFF switch.