A flow sensor includes a substrate, an electrical insulating film, and a flow velocity detection mechanism. The head has curved blades adjustable in at least an extended position and a non-extended position. , user customization of radio channel selections, immediate availability of multiple preprogrammed andor customized channels, the ability to intersperse different types of content including periodically refreshed information content, availability of personal radio functions on devices such as car audio systems, PDAs, smartphones, MP3 players, etc. The multiplexer is used to receive the upper threshold voltage and the lower threshold voltage, and output a multiplexing signal according to the digital signal.