Concern

Dear lazyweb, I’d like to know a good way to measure the amount of current a device draws. I’d like to be able to both measure the current draw over time, and get a total usage summary at the end. The goal is to mix and match workloads, sleep strategies, and different hardware components to figure out how much energy the device requires. The idea is to determine, for example, if this device ran off of a battery, how long it would last per charge (given some capacity); or if it were solar powered, how many cells it might need.

The device I’m interested in measuring is a small, embedded system. It is pretty much a stock board from the vendor, which has a single SATA disk drive attached. The power source is an external “brick,” which produces 12V DC, and it plugs into a USAian standard 120V AC source. The system runs Linux out of flash.

Of course, my first question is “will it even matter?” That is, if I throw different workloads at the device, will I even see a difference in the amount of power drawn? I assume yes,

Some of the obvious ideas are:

• Buy a simple current meter, like a “Kill-A-Watt,” that sits between the power supply and the wall outlet. That is, measure it on the 120V/AC side.
• Measure the current passing through the wire, externally. I’ve seen kits that do this (I suppose, by measuring the EM field around the wire, or something), but they cost well over $1000.
• Stick something in between the power supply and the device, similar to a Kill-A-Watt, but on the 12V/DC side.
• Solder something on the board itself (I have easy access to the board itself; I don’t have the soldering experience to do it without burning something down, though).

Of course, any technique I’d use would need to dump the info to a computer (preferably Linux or Mac), and should, hopefully, produce meaningful results. Partly I’m lost on the terminology to search for, or what kind of stores to look to.

This is for a project that I’m not sure I can talk more openly about right now, but is philanthropic in nature.