Low battery indicator (CB9133E)

This circuit was found in Maxim's documentation from the 80's. The integrated circuit is from that time, uncommon today.

IR tone remote control (CB20972E)
This circuit is from a Popular Electronics from the 90s. The circuit has a tone frequency...
Door buzzer or alarm (CB20492E)
This solar powered circuit was found in a 1991 documentation. The transistor is a general purpose...
Electronic die (CB21712E)
This circuit is based on a common cathode 7-segment display. The circuit is based on CMOS...