YF-S201 Water Flow Sensor

The YF-S201 is a Hall-effect water flow sensor designed to measure liquid flow rate in pipes for Arduino, Raspberry Pi, and other microcontroller-based projects. It consists of a plastic valve body, a magnetic rotor, and a Hall-effect sensor. As water flows through the sensor, the rotor spins at a rate proportional to the flow, and the Hall sensor converts this rotation into a train of digital pulses. Each liter of water passing through the sensor generates approximately 450 pulses, allowing the host controller to calculate both instantaneous flow rate and cumulative volume.

The sensor operates from a DC supply of 5V to 18V (minimum tested working voltage 4.5V), draws approximately 15mA at 5V, and provides a 5V TTL-compatible pulse output with a duty cycle of 50% ±10%. The measurement range is 1–30 liters per minute, with a stated accuracy of ±10% (or ±5% within the 2–30 L/min band, depending on the source). The pulse frequency relates to flow rate by the formula Frequency (Hz) = 7.5 × Flow rate (L/min), so a 10 L/min flow produces approximately 75 Hz. The sensor withstands water pressure up to 2.0 MPa (approximately 20 bar) and operates in liquid temperatures from -25°C to +80°C.

The body features G1/2 (1/2-inch) nominal pipe connections, with an internal diameter of approximately 11mm and an external diameter of approximately 20mm. The overall dimensions are approximately 62 × 35 × 35mm, and the sensor weighs about 52g. It is supplied with a 15cm three-wire cable (red = VCC, black = GND, yellow = signal). The sensor is intended for vertical installation (tilt no more than 5 degrees) and should be protected from corrosive chemicals and mechanical shock. It is a passive flow-measurement component and does not include a display, controller, or valve; these must be provided by the host system.