Simple mechanical door closer?

[salex]

Greetings! We built quite the shed, with about a third coop, third garden shed, and a third sauna! Off of the coop is a hardware cloth run of 4' x 8'. The ladies still like to run around the back yard, and we sometimes forget to close the storm door that accesses the run. The storm door shuts by spring, and I'm looking for ideas for a simple, timer controlled wedge or some such that we can prop open the storm door that would shut after sundown or a set time. I've seen all the really cool DIY and commercial door systems, but all we want is to close this door at sundown.
Thanks! Alex

 

[aart]

Have never seen of such a thing.
Could put a pop door in the run wall and a typical chicken autodoor.