When designing an add-on for an existing system:

1. Make a thorough list of what you wish to achieve.
2. Make a thorough list of resources, such as memory size, physical size, of all relevant components.
3. Gather relevant software libraries or equivalents, and make sure minimum size requirements are met.
4. If size requirements are not met, see if you are able to work around the problem through working “closer to the metal”.
5. When size requirements are met, begin design of schematics / preliminary physical model.
6. Iterate 3-5.