Check out this detailed constant current dumy load Instructable by Wingman27. It is a programmable Arduino-based instrument that allows the program a specific current to draw from a source. Wingman27 goes through the theory behind design his device enough that you'll take away a solid understanding.
I'd love to see this with a programmable power curve to simulate the discontinuous use of a power source.
I have been working in the Electrical Engineering field for quite a while now with my studies mainly focused on power. I have always had in interest in electronics but I had never really kicked off until a few years ago when a mate of mine said, "Have you seen an Arduino?". I'm the sort of person that learns by trying stuff, stuffing it up and then fixing it. I tend to be a perfectionist so it takes me a while but I am quite often happy with the result!
Source: Arduino Programmable Constant Current Power Resistance Dummy Load
Here is the EEVblog video that inspired this project.
Learn more at: http://paxinstruments.com/arduino-constant-current-dummy-load/