This filter is from the Linear Applications Handbook of the National Semiconductor of 1994. However, it can be used with other operational and modified to operate with other frequencies.
We found this circuit in an old American documentation. SCRs can be modern equivalent types. The...
We found this circuit in a 1990 documentation. The operational amplifiers are type 741 and the LED is...
This fast-acting circuit uses a 555. We found it in the November 1992 Radio Electronics magazine. The...