Input circuit for counter of ring.
In this link what would be the output logic of circuit and why output of this circuit fluctuates as input?
066bex408's circuit would be OK isolation wise as long as the ground indicated is an isolated common on the circuit board and doesn't go anywhere else......................
Second, is the circuit you posted supposed to be a phone-line ring detector? If it is, then it would make the US phone companies very unhappy; unhappy enough to disconnect your service. The circuit is referenced to ground. Big n0-n0. Niether side of a phone line must have path to ground. A ring-detector circuit must not put a dc load between the two sides of the phone line. Has to have a DC blocking capacitor,
You can use a microprocessor or other logic circuits to activate a DTMF IC generator.I'm trying to make system to control the home appliance using PSTN. I'm thinking about the feature of security so that system call or send message automatically to the owner. There will need DTMF encoder but without keypad pressing how DTMF signal or tone be generated?