Another of the many tachometer circuits we have on our site. This one is from the September 1976 Radio Elecronics magazine. The circuit is connected to the platinum contacts of a car or to a sensor.
This circuit is from 1977 documentation, but can be assembled with BC548 for Q1, Q2 and Q4, BC558...
Found in American documentation from the 90s, this circuit uses components that are still common...
This high impedance input amplifier is suitable for the use with piezoelectric sources such as...