This circuit was obtained in an Electronics World of 1968. The operational amplifiers ones are types of the time, no longer used today. The circuit responds from less than 20 Hz.
This circuit is from the 1977 GE semiconductor manual. The components used are uncommon today....
This circuit has 4 operating modes and was found in the 1995 Encyclopedia of Electronic Circuits...
The voltage of 30 V indicated in this project, shown in the figure, depends on the diac used. It...