This is a DIY chronograph for paintball, nerf, or other pneumatic guns (only) of sufficient caliber. Not for use with realsteal firearms, not accurate enough timing and especially not thermally-resistant enough bullet gates. Source code and accompanying libraries included in "OpenChrony.zip"
Full write-up hosted on NerfHaven: http://nerfhaven.com/forums/topic/28105-openchrony-open-source-diy-chronograph/
The new source code is in "OpenChronyV1.5f.zip".
Print "V1-5_Electronics_Box_Top.stl" in place of "Electronics_Box_Top.stl". The other files are the same for both versions.