Abstract: A photoelectric sensing system, the adjustment of which is facilitated by the incorporation therein of a contrast indicator with a display in the form of an array of light emitting diodes (LEDs) controlled by a driver circuit which is arranged for successive illumination of the LEDs, preferably on a one-to-one basis. This bargraph type instrument is also effective in photoelectric sensing tasks involving variations of the detected light between "light" and "dark" at a rapid rate, in which case the range of LEDs between these two extremes appears dimly lit at a steady glow.

Abstract: A start/stop control arrangement for material handling systems, particularly automated checkout systems in retail stores. From a beam sensing device at the delivery end of the incoming conveyor a control is derived not only for stopping the conveyor in response to the detection of the arrival at that end of a product but also a time control for automatically stopping the conveyor in response to no such product being detected by that device for a predetermined time. The arrangement may be incorporated in the amplifier unit which serves to amplify the output of the beam of the beam sensing device. Alternatively, and as shown herein, the arrangement may be implemented by a plug-in accessory module designed to be interposed between two cooperating plug-in modules--one of them mounting the above sensor amplifier--which provide for the first of these two controls only. Provisions are also made for double-using the arrangement for the start/stop control of the conveyor outgoing from the checkout stand.