The circuit shown was found in the 1994 National Semiconductor's Linear Application Handbook. The op amp admits equivalents and the power supply must be symmetrical.
This bench photometer, suitable for professional photographers, was published in Radio Electronics...
This low-pass filter with 741 op and symmetrical source was found in the August 1993 issue of...
In the original publication of the 90s a 556 consisting of a double 555 is suggested. The circuit...