My tachometer design is as in the Figure 20. ”Speed Switch”, Load is Energized when fIN ≥ (1 / ( 2RC)). I set up this circuit on the board but my design dont work. Lm2907's pin8 must change state after input frequency is 1850 hz. But this process was done all frequency range. The only difference is going more slowly at low frequencies.
DESIGN DETAILS ARE ADDITIONAL.