How to invert a pulser and connect a door to it?

Solution 1:

So, first off, here's what a basic pulser with an enabling switch looks like.

The problem with connecting a door – or anything – to this contraption via Redstone is that the relative torch will no longer be part of the pulser. I'm not going to think about why is that – this is a weird contraption anyway – so here's the workaround:

The door needs to replace one of the non-vital torches.

The vital torches are those connected by the middle Redstone cross. Everything else is non vital (= removing it won't break the pulser) and can be replaced by a door in place.

Another important thing to remember is that the switch must not be right next to the door, or the current will simply flow from the switch to the door directly, ignoring the pulser entirely.

In this unpolished proof of concept, I brought the switch forward and replaced one of the side torches with a door. Since the door is directly wired to the pulser, it pulses with it.

It is incidentally a little known fact that you can extend pulsers at will by adding more blocks with Redstone on them and non-vital torches on the sides.