This circuit was found in the February 1985 issue of Radio Electronics magazine. It is based on an AY-3-1350 melody generator that was common at the time. It is suitable for analog lines only.
The circuit shown in the figure is suggested by Allegro Micro (www.allegromicro.com) and consists of...
This circuit is a variation of the common grid dip meter, having been found in a 1975 publication on FETs....
The time obtained in this circuit, from a 1978 publication, depends on R3 and C. R3 can have...