ELECTRONIC TONE RINGER

摘要

The electronic tone ringer of the present invention comprises a rectifier circuit connected across the tip and ring leads of a telephone loop to provide a d.c. voltage. The d.c. voltage is connected through a timing circuit to the inputs of a sounding device. The timing circuit includes a timing network, which is connected across the d.c. voltage for establishing a predetermined time delay. The timing network controls a first transistor which in turns controls a second transistor. The second transistor is connected across the input of the sounding device so that prior to the expiration of the predetermined time delay, the second transistor shunts the inputs of the sounding device to assure that the sounding device is not erroneously activated by a short duration transient voltage across the tip and ring leads.