Visual indicating control circuit in key telephone system

Details Visual indicating control circuit in key telephone system Visual indicating control circuit in key telephone system

1975-03-14

1976-07-27

Claffy, Kathleen H.

179 81C, H04M 122

Patent

active

039718980

ABSTRACT:
A visual indicator control circuit for use in key telephone systems is disclosed. The circuit includes a plurality of light emitting diodes connected in series and operated by a plurality of transistors having collector-emitter paths connected in parallel with the light emitting diodes. Circuits are provided for controlling the respective base electrode voltages of the transistors corresponding to the use status of each line to control the light emitting diodes corresponding to the on or off states of the transistors.

REFERENCES:
patent: 3469036 (1969-09-01), Meri
patent: 3566044 (1971-02-01), Cross
patent: 3567868 (1971-03-01), Mukae et al.
patent: 3819871 (1974-06-01), Verdon
patent: 3842216 (1974-10-01), Owen et al.
patent: 3931479 (1976-01-01), Warman et al.

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