Digital Volt Meter AMP Meter DC 10A 0-100V Screw Terminal It's an optical sensor that

It's an optical sensor that measures the absorbance of pulsating blood through a photodetector after emitting two wavelengths of light from two LEDs - a red and an infrared one

and so forth

indicating that the digital output pin will be 0V

Material Plastic Button Colour  Red Terminal Type  Soldering Mounting Panel Mounting

Digital Volt Meter AMP Meter DC 10A 0-100V Screw Terminal It's an optical sensor thatIts digital voltmeter, Voltmeter is an instrument used for measuring voltage (V), that is the potential difference present between any two points within a circuit. Features: 0. 28 device with 5 wires divided into 2 sets. Black, Red are for the power supply and 3 wires to measure the Voltage and Current. Very small and lightweight voltmeter module. Very handy and easy to use. Specification Voltage supply range 4. 5V to 24V Voltage measurement range 0