Using the LM358 from Texas Instruments, this circuit uses LED indicators and can be powered with voltages of 5V or according to the analyzed logic.
An interesting timer is shown in the figure, using one of the 4 NAND gates of the integrated 4001....
General Electric suggests this circuit in a 1980s documentation. The operational of the time is...
This simple adjustable source uses a PNP transistor that can be the BD136 for even slightly higher...