Hi Urs, Thanks for the clarification. I think now I understand your setup. Only a few more questions:
1. Using your example, then the voltage on the mote itself is the remaining from 3v - 0.2v = 2.8v. Is this right? 2. How would you correlate the measurements on the Oscope to the events on the mote? Did you have to instrument any code? 3. I am curious about the model of the Oscope in your test. I know Janos used HP34401A. Is there any model you would recommend for this task? Thanks. David On Thu, May 14, 2009 at 7:33 AM, Urs Hunkeler <[email protected]> wrote: > Hi David, > > I'm not sure I understand your diagram. I would draw the diagram as shown > in the attached image file (if it gets through the filter). > > Let's say that the plus terminal of the power supply is connected to one > terminal of the resistor. The other terminal of the resistor is connected to > the plus terminal of the battery connector of the mote. The minus terminal > of the mote is directly connected to the minus terminal of the power supply. > The ground connector of the oscilloscope is connected to the plus terminal > of the battery connector of the mote (which is also connected to one > terminal of the resistor). The measurement terminal of the oscilloscope is > connected to the plus terminal of the power supply (which is also connected > to the other terminal of the resistor). > > Thus, the oscilloscope is measuring the voltage drop over the resistor. > This voltage drop is proportional to the current being drawn by the mote. In > fact, the voltage over the resistor V_R is: > > V_R = I_M * R = I_M * 10, > > where I_M is the current drawn by the mote. So if the mote draws 20mA of > current (e.g. when the radio is in receive mode), then the voltage drop > measured over the resistance is 200mV = 0.2V. > > So far, I have not used any simulations for power measurements and can't > comment on this. > > Cheers, > Urs > > > David Li wrote: > >> Urs, >> >> Sorry I forgot you used 3v lab power supply. So I revised my diagram as >> following: >> >> >> >> >>> >>> +-----------------------------+-----------------------------------+-------------------+ >>> | >>> | | | >>> mote resistor (1 or 10 Ohm) 3v Power >>> Oscilloscope or multimeter >>> | >>> | | | >>> >>> >>> +-----------------------------+-----------------------------------+-------------------+ >>> >>> >>> >>> >>> >>> David >>> >>
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