Pledging mechanism using Bitcoin Is there an obvious way that I can achive the following with Bitcoin?


An organizer sets a goal: an amount of bitcoins must be gathered within a specific amount of time
Random pledgers send an amount within specified boundaries (min/max amounts).
If the goal is reached within the specified amount of time, the organizer collects the pledges
If the goal is not reached within the specified amount of time, the pledges are returned to the pledgers


AFAIU the above model is similar to Mike Hearn's LightHouse project, however I cannot use this great platform for my project and on top of that I would like to be sure that I'm headed in the right direction, so any ideas and alternatives on how to achieve the above are more than welcome.
Have a look to https://bitcoin.org/en/developer-guide#term-sighash-anyonecanpay
SIGHASH_ALL|SIGHASH_ANYONECANPAY

Organizer creates transaction with one output and none inputs. Any person can add his funds to this transaction. Once the needed amount is collected the transaction can be sent to a network.


  An organizer sets a goal: an amount of bitcoins must be gathered
  within a specific amount of time


Seems to me that specifying amount of time is not possible


  Random pledgers send an amount within specified boundaries (min/max
  amounts).


Fixed amount.


  If the goal is reached within the specified amount of time, the
  organizer collects the pledges


Let us say "if the goal is reached one time the organizer sends this transaction to a network".


  If the goal is not reached within the specified amount of time, the
  pledges are returned to the pledgers


Any pledger can re-spend his funds at any time before organizer creates valid transaction