741 Filter (CB24265E)

The 1 kHz tuned filter shown uses a 741 op-amp. The components can be re-scaled to suit the desired frequency.

Oscillator using a Comparator (CB13145E)
Frequencies up to just over 100 kHz can be obtained with an oscillator based on one of the four...
Metal Detector (CB22460E)
This circuit, found in a Popular Electronics from 1992, is based on an oscillator and a crystal...
Open Collector TTL Gate (CB24884E)
This is a discrete equivalent version of an open collector TTL gate. What we have is an inverter...