Door buzzer or alarm (CB20492E)

This solar powered circuit was found in a 1991 documentation. The transistor is a general purpose NPN.

FETs Integrator (CB19375E)
This integrator circuit uses the junction FETs which can also be the BF245 or MPF102. The...
Battery charger (CB1225E)
This 6 V battery charger was found on a 1987 Hands On Electronics. Rc determines the charging...
Constant torque control (CB7936E)
Found in an American publication from 1968, this circuit aims to keep the torque of a DC motor...