The binary size (32768) does not look right. It should be a few hundred bytes less than that. Note that if you are downloading 1.8.2.hex firmware as an individual file, you should use the ‘Raw’ file link in GitHub, not ‘Save File As’, or ‘Save Link As’. Here is the direct raw file link of firmware 1.8.2 for OpenSprinkler v1.4:
https://github.com/rayshobby/opensprinkler/raw/master/OpenSprinkler%20Controller/software/compiled/v1.4/firmware1.8.2.hex