Found in old documentation, this circuit is tuned to pass signals below 245 Hz with a level of 0.044 dB above 500 Hz.
Found in the documentation on PCs, this circuit excites LEDs whose current is determined by R3....
We found this circuit in a 1977 technical documentation. The FET can be the BF245 and the bipolar...
This 1977 circuit only allows the solenoid to energize if the right combination of switch...