Abstract: Where several telephone sets are connected to a single telephone line, it would be convenient to have a visual indication that the line is in use, to avoid lifting a handset to see if there is a conversation, for example. A circuit is installed across the telephone line, the circuit having a voltage divider connected between Tip and Ring, a first transistor with its base connected to the center of the voltage divider, a second transistor with its base connected to the collector of the first transistor and a third transistor having its base connected to the emitter of the second transistor, with a light emitting device connected between either Tip or Ring conductor and the collectors of the second and third transistors. The light emitting device can be a light emitting diode. An optical coupler cooperative with the light emitting device can be used to turn on power to light emitting devices in all the telephones, from a separate power source.

Abstract: An electronic hold and hold-release circuit for a telephone set in a multiple extension single line telephone system has an indicator in either the tip or ring line, an electronic switch, such as a SCR, across the lines and a manually operated momentary hold button which, when operated after picking up the handset of the telephone, switches the electronic switch device to a conducting state and provides a hold current on the lines, the hold current maintained after replacing the handset. The hold condition is indicated by the indicator. An electronic device in one of the lines prevents current flow when the line voltage drops to about 10 volts, when another telephone handset is picked up, switching the electronic switch to a non-conducting state and releasing the hold. A bridge diode arrangement enables operation on either line polarity. Conveniently the indicator is an LED. Lightning and other voltage surges can be restricted by a resistor.