This simple circuit to monitor the frequency of the power grid uses an analog indicator. The adjustment trimpot can be 4k7 and the indicator is 100 mA full scale.
The presented circuit is suggested by Texas Instruments (www.ti.com) in its Application Report...
This circuit with an industrial standard 4-20 mA interface uses a KPZ20G pressure sensor but can...
This circuit takes advantage of the inductance of the coil of a high-impedance phone to form the...