The circuit presented was suggested by Texas Instruments in an opto-electronics manual. The transistor can be the BC548 and the supply voltage depends on the application.
This circuit was suggested by Popular Elecronics from the 90's. The circuit has high input...
Figure 1 shows a circuit than can be used as time stage in timers, and other applications....
This circuit is from a Popular Electronics from 1993. The magazine is no longer printed, but the...