Tiny Cooling Fan monitor mode

Although DC "Tiny Cooling Fan" has a high reliability, but it is still mechanical devices. When long-term use, the fan speed and cooling efficiency may fall or fail, so the fan continuously monitored. Many "Tiny Cooling Fan" Manufacturers provide different monitoring methods, generally divided into: alarm sensor and speed sensor types. Use alarm sensor in the fan speed is lower than an alarm signal when a certain threshold. And some "dota雷竞技 " Manufacturers are given with the speed sensor output signal proportional to the frequency of fan speed, usually every turn Lou produce two pulses. Alarm sensor and speed sensor can provide a pull-up drain or internal, internal pull can be TTL level or supply voltage.