I have a problem. I can read out the tachometer of a PC fan and convert it to frequency with just using a simple microcontroller and labview.
Does anybody here have an idea how to read out the tachometer, without powering the fan? I want to measure the RPM with manually spinning the fan. I want to use the tachometer to measure the frequency of a shaft of a low rpm mini-engine. When I disconnect the power that makes the fan rotate, i do not get a reading anymore from the tacho, even when the blades are still spinning.