Amazon.com: Digital Counter, Easy Connection NPN PNP Signal Input Stable Electric Counters Auto Detection for Industrial Control : Industrial & Scientific
Amazon.com: Water Level Sensor, XKC-Y26-NPN/PNP Non Contact Liquid Level Sensor Switch/Water Level Controller/Water Level Gauge(XKC-Y26-NPN 24V) : Industrial & Scientific
Transistor Assortment, Npn Transistor Transistors Assortment Kit for Industry for Plug Transistor for PNP Transistor for 2n3904 Npn Transistor: Amazon.com: Industrial & Scientific