Measuring Power Consumption of Devices
How to determine how much power a board or component is consuming
A problem you'll have to deal with again and again when developing portable devices is how to optimise them to use as little power as possible while still providing an appropriate level of functionality and performance. For example, the faster you run the MCU the quicker it will respond, but it will also consume more power. You'll also have to answer all kinds of questions like "what kind of power source is appropriate in my situation?", with each possible answer likely having it's own tradeoffs and compromises. Should you use batteries? If so, Lithium Polymer, NIMH or NiCAD (and why)? Solar power? How many mA and volts, what physical size for the cell, and how will you ensure an adequate power supply when there isn't enough sunlight?
Unfortunately, there's no magic bullet to designing and building low-power devices, and it's often an iterative process with many little steps and refinements, and a lot of testing and retesting. Before you can begin trying to optimise a product design, though, you'll first need to answer the most basic question: "how much power am I currently using"? If you have a multimeter that is able to measure the flow of current in mA, simply set your meter to the appropriate setting and put your meter 'in-series' (between the power source and the device) as follows:
This should bring up a number (in mA) representing the amount of electrical current being drawn by your device. If you get a negative value, simply switch the position of the + and - probes on your multimeter. It's as simple as that!
Be sure not to try to measure a device that will probably draw more current than your meter is able to measure! For example, many inexpensive meters can measure 200mA, which is more than most small development boards use. If you were to try to measure a large device using 1A, though, you would almost certainly blow a fuse in the meter.