Linear Ohmmeter LM11 and TL431 (CB14548E)

We found this circuit in Motorola's Linear Databook in 1990. Integrated circuits are somewhat difficult to obtain today.

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...