Low battery indicator 555 (CB9551E)

This circuit can operate with different voltages, depending on the zener used. We found it in a 90s American documentation.

100 000 Mohm Step for Multimeter (CB12282E)
With this circuit it is possible to obtain an input resistance of 100Gohms for a multimeter, with...
Medical Amplifier (CB1464E)
This amplifier, to detect biological signals in implanted transmitters, uses transistors such as...
Parallel Port Interface for PC (NI021E)
This application is not modern since few computers have parallel ports. But you can use this...