This circuit was obtained in a Hands-On Electronics from the 90's. The circuit turns on one LED at the end of the timer, erasing the other. The timing can be increased by increasing C1.
I found this circuit in an old Argentine publication from 1973. The components are no longer...
This circuit has an LED indication of the timing progress, having been found in an old...
This simple signal tracer was found in a Popular Electronics from the 90's. The transistor can be a...