Telephone Busy Indicator (CB24430E)

This circuit for analog telephones from the 90s was found in documentation from the time. It lights up a remote LED when the extension is in use.

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Two Stereo Light Effects (CB17150E)
This circuit was found in a 1999 publication. Its purpose is to flash two LEDs according to the...
Digital Multimeter (CB18680E)
This circuit is based on the well-known digital module ICL7107 feeding 4 displays with...
Square Oscillator LM3900 (CB17389E)
This configuration can be found in other articles in this section. This was obtained in a 2000...