The NJL5165K series from Nisshinbo Micro Devices Inc. are reflective optical switches that use phototransistors as their output devices. These switches work by emitting infrared light and detecting its reflection off an object, which then triggers the phototransistor to switch states. They come in various configurations, including surface mount and through-hole types, making them versatile for different PCB layouts.

These switches are commonly found in proximity sensing applications, such as level detection in industrial machinery, presence sensing in security systems, and automated door openers. They also show up in consumer electronics like remote controls, where they help detect the position of buttons or switches. One practical benefit is their ability to operate reliably in harsh environments due to their robust design and low power consumption. Engineers tend to reach for these when they need a simple yet effective way to sense objects without physical contact, especially in confined spaces or where mechanical switches might be prone to wear and tear.