公开(公告)号：US20210005078A1

公开(公告)日：2021-01-07

申请号：US15733642

申请日：2019-03-18

Applicant: BRITISH TELECOMMUNICATIONS PUBLIC LIMITED COMPANY

Inventor： Mohammad ZOUALFAGHARI ,  Michael FISHER ,  Ian NEILD ,  Michael WILLIAMSON

IPC: G08B29/10 ,  G08B5/36 ,  H03K17/687

Abstract: A passive sensor for detecting the operation of a light source includes a photosensor which, when illuminated by the light source, delivers a voltage to a field effect transistor (FET) which can switch a circuit to control a device at a remote location. The FET transitions rapidly between very low resistance (short circuit) and very high resistance (open circuit), allowing a binary indication to be given in the circuit. The circuit can be used to charge an electrical storage device to allow later download of recent status of the lamp by detecting the charge stored in the device.