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 "Tiny Cooling Fan" 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.