This tach will work on the signal from the W terminal on the alternator The Bosch alternator that i used gave 6 pulses on the W terminal and the ratio between the cranck and the alternator is 1:2,38. When you calibrate it do it on the higest RPM possible you get a better reading on lover RPM:s. If you calibrate it on 5000 RPM the input signal is 1190Hz (5000RPM/60)=83,3r/s 83,3*2,38*6=1190
modelled in proteus
The line from pin 7 coupled to groung via C1 is causing me concern...