This simple flow sensor is very similar to its big brother, the YF-S201, but has been optimized for lower flow rates and features a higher pulse per liter count. Inside the housing, a small pinwheel with an attached magnet is spun by passing water; as the magnet makes each revolution, a hall effect sensor inside the housing outputs a pulse on the yellow wire.

This sensor is best suited for flow rates between 0.3 and 6 liters per minute and outputs 5880 pulses per liter (approximately 1 pulse per 0.17mL). The sensor has a barbed 7mm hose connection point on each side with an inner diameter of 4mm.