Portable through-door intercom

Details Portable through-door intercom Portable through-door intercom

1989-05-26

1990-01-16

Schreyer, Stafford D.

Telephonic communications

Private or single line system

Doorbell system

379110, 379435, 379454, H04M 104, H04M 904

Patent

active

048948586

ABSTRACT:
A through-door security intercom that clamps on the free edge of a door of any conventional thickness. Clamping is effected by constant-force flat springs, which springs also provide current paths. The springs are pre-bent at acute angles at predetermined points, to aid in mounting of the outside unit on the door. The inside unit is mounted on the door due to the force created by the constant-force springs which are coiled on spools. Brushes in the inside unit engage the springs and complete the electric circuit.

REFERENCES:
patent: 4130728 (1978-12-01), Grauel
patent: 4584436 (1986-04-01), Boenning et al.
patent: 4631365 (1986-12-01), Potter et al.
patent: 4809320 (1989-02-01), Hawkins et al.

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