Use the oscilloscope to visualize the current drawn by a receiver board.
Zoom in onto a wake-up period and use the averaging function on your oscilloscope
(on the TDS2022B press acquire, average) to average over asmany samples as possible.
Freeze the screen once this is done, you should obtain a screen close to the following one:
Energy consumption measured when sampling the channel.
You easily see the different phases when the CC2500 is turned on, the current
drawn during these phases and their length (see Table below).
As shown in the following table, you can calculate the average current consumption of the
board when it is listening, and the expected lifetime.
Phase
duration
av. current
idle
99.6ms
0.788mA
A
microcontroller startup
0.396ms
5.45mA
B
radio frequency calibration
0.772ms
9.55mA
C
reception mode
3.24ms
18.3mA
D
entering sleep mode
0.032ms
5.00mA
Duration and average current consumption of the different phases observed in the figure. Measurements averaged over 128 samples.
One can calculate that the average average current consumption is 1.450mA, hence an expected lifetime of about one month on 1000mAh.
By carefully tuning the value of
CI and
Dcca (which was not done here for simplicity), the energy consumption of a preamble-sampling MAC protocol can be brought down below .1%.
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Source:
OpenStax, Ezwsn: experimenting with wireless sensor networks using the ez430-rf2500. OpenStax CNX. Apr 26, 2009 Download for free at http://cnx.org/content/col10684/1.10
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