This filter has the components calculated for the frequency of 1 kHz but can be changed. The input resistor can be 100k and the source symmetrical. Any operational amplifier can be used.
The original frequency of the Pierce Oscillator with bipolar transistor is given by the crystal, which...
This series LED circuit was found in the February 1992 issue of Radio Electronics magazine. The...
I found this circuit in a Popular Electronics from 1992. The circuit can be easily implemented with BC549...