There’s an annoying subtlety in the Arduino IDE when using tabs (multiple files in the sketch), that was kindly explained by PaulS on the Arduino forums.
Any Arduino libraries that are needed by the files outside of the sketch (.ino) file must also be listed in the sketch file itself.
You cannot simply do this:
When you attempt to compile, you’ll get an error like,
In file included from test_junk_02.cpp:1: test.h:7: error: 'Servo' does not name a type
You must also include the library in the sketch:
The explanation that PaulS gave was the following:
The sketch is parsed for include files. The sketch, all included header files, and the corresponding source files, are copied to another directory for compiling. From that directory, library-based include files are NOT available unless they are included in the sketch and copied to the build directory.