NPN PNP Signal Converter, MRI-24TR/INV PLC Sensor Polar IO Level Conversion Module, PNP to NPN Signal Converter Relay: Amazon.com: Industrial & Scientific
uxcell 4mm Inductive Proximity Sensor Switch Detector NPN NO DC 5-30V 200mA 3-Wire SN04-N for 3D Printer Probe Bed Leveling,MCU Board: Amazon.com: Industrial & Scientific