I'd like to create a simple circuit for keeping a line "high" for a few seconds after being triggered high, without any external power.
To specify it in more detail: given three inputs, 3.3V, GND and a processor output line that can be driven high, create a circuit that drives an output line high for 5 seconds after being triggered by the processor output line, even when the 3.3V line goes dead. The timing doesn't need to be exact.
Theoretically, I guess this would be easy by just hooking up a capacitor and a thyristor together. However, suitable thyristors do not seem to be easy to find, and fitting together all the component values seems tricky.
This is also similar to all the power-on / power-off delay circuits, but a little different.
So, I am looking for better ways to do this.