When Pistons first came out I tried to make a complete wall of them, but it didn't work, purely because I was wiring it wrong. But I went back to it today and made this.

It works how I would like it, and better still I made a schematic and a world file for it.

Additional Notes

The schematic will may break the pistons, they'll point down, so you'll need to manually replace them to get it working. World file should be working.