Charger protection relay (CB26312E)

This circuit was obtained from an Elektor magazine from the 90s. The circuit is to protect batteries while charging.

800 Hz tone generator (CB18973E)
This circuit generates a continuous 800 Hz tone on a small speaker of 8 to 16 ohms. An amplifier stage...
Saw tooth (CB8888E)
This circuit has a general-purpose transistor to compensate for the non-linearity of the generated...
High gain audio amplifier (CB8938E)
This high-gain circuit was found in an American publication from the 1990s. The circuit can use...