pam-test-stand.ino: global variables and utilties not placed in ./src/
daq.ino: data acquisition app
src/<Library>: library
The main .ino file is always included. The Arduino CLI concatenates all
.ino files, therefore the applicatiion to be compiled is defined by an APP_<name>
define directive passed into the arduino-cli invocation, and each app will
have a matching #ifdef to include or omit its code.