On Friday 06 April 2007 13:57, Philip Levis wrote: > On Apr 6, 2007, at 12:27 PM, Kurt Peters wrote: > > If you seek to estimate the power consumption, you can read > > through the > > data sheet for the 128L from Atmel if you're using that group of > > motes. [snip] > > One of the issues here is that the range of currents make it very > difficult to measure with a single set-up; there's four orders of > magnitude difference between the lowest and highest draws. > > The approach that being seem to be settling on in the research > literature so far is to perform microbenchmarks of specific states > using a precision multimeter, correlate those values with the > observed but inaccurate oscilloscope values, use an oscilloscope > trace to determine how long the node spent in each state, and > calculate the energy that way. This mostly matters for sleep currents > -- the oscilloscope readings are go good for things like the radio > being on. > > I'm sure there are better and more complex measurement setups to do > this more accurately, but this approach seems to be pretty effective.
[OT] You mean like this one? ;^) We coupled high-bandwidth precision power supply with a precision resistor in series with its output *before* the voltage feedback path. We power a sensor node with this guy, then use a high-speed DAQ to capture the voltage drop across the precision resistor and the PS output voltage at high speed (>10MHz). We can then graph the voltage, current and power consumption over time. By having the sensor node twiddle a couple of digital outputs sampled concurrently, we also get a time reference for notable events. We didn't build this to create power consumption models but to measure power state transistions. As an example, our board uses a lithium battery, so the design includes a voltage regulator. We initially selected a very efficient, low-Q part. But testing has shown the original VR was woefully inadequate in terms of bandwidth and couldn't maintain desired regulation during many types of power events. The moral for me has been: even though we're talking about small currents in sensor nodes, the relative magnitude of spikes and slopes in power draw can be significant. Steve _______________________________________________ Tinyos-help mailing list [email protected] https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
