Variable oscillator for code practice (CB7317E)

This circuit is from Popular Electronics from the 90s. The integrated circuit is not very common nowadays.

Low Pass Filter (CB5198E)
This circuit uses only passive components calculated for the desired frequency. We found it in an...
100 Hz High Pass Filter (CB6545E)
This fourth-order circuit was found on an 80's Radio Electronics. The power supply must be...
Resistive Sensor LED Control II (CB1299E)
This simple circuit controls the brightness of an LED from LDRs, NTCs, PTCs or other resistive sensors....