This integrating circuit multiplies the time that can be obtained with a 555 timer. We find it in an Electronic Design from the 90s. The circuit uses components that are still common today.
We found this configuration in the Linear Applications Handbook of the National Semiconductor of...
This circuit is an application for an operational amplifier with field effect transistors from...
This circuit was found in an old Radio Electronics, but can still be assembled as the components are...