Inside a Vintage “Electric Eye” Receiver

One transistor and a clever relay circuit is all it takes to switch or latch devices when a light beam is interrupted. This is the first time I’ve seen a television set used as an indicator light. Knight was the brand of Allied Electronics, used both for gadgets like this and Knight Kits, which were a down-market competitor of Heathkit back in the day.

Allied Electronics sold its consumer electronics business to Radio Shack in 1970, which ran it into the ground. Allied is now a mainstream electronics distributor specialising in industrial automation components. Allied continues its tradition of selling in small quantities to individual designers and hobbyists as well as large-volume industrial customers.