This circuit was found in a Popular Electronics from the 90s. The transistors are general purpose, and the gain depends on the ratio between R2 and R1.
To obtain a signal with a variable mark / space ratio in a ratio of 1 to 20 to 20 to 1, we have...
Found in an Electronic Engineering from the 80's, this circuit makes use of components of the...
This circuit, which can use a reed sensor, is indicated for doors and windows. The circuit was...