This signal injector and tracer (follower) was found in an old American documentation. The transistors can be general use and power is made with one or two common cells.
This circuit is from a 1998 Poptronics. The circuit triggers a buzzer after a certain time, waking...
An integrated circuit 741 (operational amplifier is the basis of this voltage indicator, which can also...
This transistorized voltage converter is one of the oldest that we find in technical publications. It...