Found in Popular Electronics from the 90's, this circuit uses 555 integrated and common transistors to generate two tones determined by push buttons S1 and S2.
This excellent circuit came out in a Japanese publication from 1971. It uses Japanese transistors of the...
This circuit is from the owner's manual of the integrated circuits used. The manual is old, which...
We found this circuit in an English documentation from 1995. The Hall sensor used is from the time...