Additional mod to the tach:
1. Added ST L7812 voltage regulator to the circuit. Stabilize the input voltage to 12V
2. Added a 220uF cap on the regulator output.
3. Cleaned and assembled
Test will be carried out on weekend on my VWs.
Semi-finished tachometer
Final Tachometer calibration result, (Based on industrial HP signal generator)
Input frequency, Theoretical Tach reading, Actual reading, Repeatability, remark
50Hz ; 1500 rpm ; 1600 rpm ; good ; Conditional accept
100Hz ; 3000 rpm ; 3000 rpm ; good ; Accept
200Hz ; 6000 rpm ; 6000 rpm ; good ; Accept