Phone Line Simulator
projects that connect to the phone line can be a real chore without some
device like this. It generates the 48 volts DC for the on-hook condition,
the 100 volts AC for the ring signal, and the 20 milliamperes DC for the
To use the device, a phone is connected to the left jack. When it is picked up (off-hook), a ring signal is generated at the right jack. When the device on that jack goes off-hook, the ring is terminated, 20 ma is provided thru 600 ohms, and the 2 lines are connected for audio. When the phone is hung up, a 250 ms line break is created on the other jack to indicate the end of the phone connection.
This allows testing of incomming phone devices only (i.e. answering devices).