I didn’t want to download any software or use anyone elses web service. I wanted to use Windows and nothing else.
Git hackups, LAMP stacks or unixesque “wget” solutions are not prerequisites for backing up your Trello boards automagically.

Powershell v3 (Windows 8) solution:

Grab an API key and a user token from https://trello.com/1/authorize?key=APIKEYHERE&name=TrelloBackup&expiration=never&response_type=token

Replace [key], [token], [board] and [filepath] below. Run in Powershell or save as .ps1 and schedule using Task Scheduler.

Invoke-WebRequest “https://api.trello.com/1/boards/[board]?key=[key]&token=[token]&actions=all&actionslimit=1000&cards=all&lists=all&members=all&memberfields=all&checklists=all&fields=all” -OutFile [filepath].$(get-date -f ddMMyyyy).json