On Mon, 12 May 2014 09:13:20 -0700, Jeff Liebermann
wrote:

On Mon, 12 May 2014 07:48:48 +0100, N_Cook wrote:

You used to be able to get neat simple "timer" buttons for stairway
lights, on for the duration of climbing a flight, but should work for
DC. They must have had a piston in a cylinder with a spring return. You
pressed down on the button to expel the air from the cylinder, a flap
valve closed and then air would probably be admittted along a long
capilliary tube , coiled up somewhere inside. Gave timing on of about 1
minute

Good idea. Googling for "pneumatic push button", I find:
http://www.alarmcontrols.com/html/our_product.asp?action=view&ID=28
all of which I think will work. They also have electronic versions,
but I think pneumatic is more cool.

Available on eBay:
http://www.ebay.com/sch/i.html?_nkw=pneumatic+push+to+exit

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558