Band-Pass Filter (CB14921E)

This circuit was found in a Poptronics of the 90's. The components can be changed to the desired frequency. The power supply must be symmetrical.

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Resistive Sensor LED Control II (CB1298E)
This simple circuit controls the brightness of an LED from LDRs, NTCs, PTCs or other resistive sensors....
Audio Controlled Switch (CB21262E)
This sonic relay or vox was found in a Popular Electronics from the 90's. The power MOSFET can be of...
Optical Shield TTL – I (CB1323E)
This circuit has been found in an old documentation, but can be used as input shield for current...