These are simple devices, with an infra-red emitter and a photo-transistor, both facing upwards, but work at an unusual wavelength. “These contain both emitters and detectors for 940nm wavelength,” ...
Remember pandemic shortages? In your household, it may have been toilet paper, flour or chicken wings. For Maine's about 150 craft breweries, the COVID-19 pandemic engendered scary shortages of CO2, a ...