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MSP430G2553 Workshop

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Hi,

I have been working through the MSP430G2553 Workshop and have just finished Lab 6.  Running the code from Lab6c.txt in the supporting files does not give me quite the same results as in the video: the green LED does not come on, and the current draw on my Digitor Q1585 DMM shows about 20uA, not the 0.6uA I was expecting.

Does anyone know whether my LaunchPads may be faulty (I have tried the example on 2 with the same results) or whether my DMM does not have a sufficiently low effective resistance?

I am reluctant to continue with the Workshop until I am sure I will be able to achieve the maximum power savings for my project.  My LaunchPad is ver 1.5 with the MSP430G2553 MUC as in the video.

Many thanks,

Mark 

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Mark,

Are you trying to read your current consumption while connected via the USB?  If so, you will not see an accurate reading. 

To get accurate readings of current draw, you will probably want to power via an external source, and read across your input. In the pre-launchpad days the experimenter boards had a power jumper that allowed an easy means of measuring current (and you still had to disconnect the JTAG and reset). I think you can still accomplish the same by removing the Vcc jumper and measuring across the supply, but make sure you're not connected to the debugger, as it will skew your readings.  The value you're seeing is reminiscent of the debug interface being connected and running.

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Hi Rei and NurseBob,

Thanks for your responses.

Rei, yes the green LED jumper is on, and no, the green LED pin is not shared - as per the Workshop video, the LaunchPad is stand-alone, only connected via the USB cable to the computer.

NurseBob, I have tested the project in Release mode and the power consumption drops to about 10-17uA, but the reading fluctuates a fair amount.  Interestingly, if I hover my hand over the top of the LaunchPad the power consumption goes up to 60-80uA but again very variable!?  The vidoeo in the Workshop does not show such fluctuations, and I can't understand why mine is so unsteady.  I have also powered the LaunchPad using a 3V battery through the DMM but this gives me a nonsense reading of about 12mA (stable though).

I'm thinking it must be my DMM unless you can think of any other reason.  I am concerned, though, that my final project may not operate for years on a battery as the calculations suggest if the power consumption is in the 20uA range instead of ~1uA.

Thanks again,

Mark

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Have you made pullup, or pulldown on all unused inputs, or put all unused pins for output.
An input collects noise from the surroundings as you see.

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Hi Frida,

Thanks - those are good thoughts.  The Lab example has the following code which I assumed handles the inputs and outputs:

void ConfigPins(void)
 {
  P1DIR = ~BIT3;                                 // P1.3 input, others output
  P1OUT = 0;                                       // clear output pins
  P2SEL = ~(BIT6 + BIT7);                // P2.6 and 7 GPIO
  P2DIR |= BIT6 + BIT7;                     // P2.6 and 7 outputs
  P2OUT = 0;                                      // clear output pins
 }

Would that code not be sufficient to prevent noise from any un-terminated input pins?

Thanks,

Mark

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Hi All,

I think I have discovered something, but I'm not sure what!  I noticed when I turned my LED desk lamp off the consumption rose, and fell again to it's ~12uA level when I turned it back on.  Also, the LaunchPad was on my desk quite close to my laptop.

I then dangled the LaunchPad over the edge of the desk on the USB cable (ie. in the shadow of the lamp, and below the level of the laptop), and the power consumption went down to a steady 0.6uA as in the Workshop video!  The power consumption still shoots up if I move my hand close to the LaunchPad...

Thanks for all your help,

Mark

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re: battery life and power consumption - if you're not already subscribing, you can find some very, very useful information in Jack Gansssle's news letter. This reference on low power design and why performance may fall short is informative.

Your comments regarding DMM and changes to readings: Yes, you may want to invest in a meter that is more reliable at the uA level.  And, sounds like there might be a capacitative aspect or inductive aspect to your measurements???  Also worth exploring, how you are taking your readings.  Definitely above my pay grade... :)

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Unrelated to your post, but to your location - I had the good luck to spend a couple of days in Sydney last August. (I was going to say "summer" then remembered that the seasons are subject to equatorial influence.)  Also located somewhere near you, and another good reference if you're just getting into electronics, etc., is Dave Jones' video blog. Entertaining and educational.

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Hi NurseBob. Thanks for your latest messages. The reference on low power design is great and will certainly help. You are correct in your assessment that l am "just getting into electronics" : I am 70 and a recently retired engineer and loving getting into hardware after decades of (self-taught) programming. Hence the sometimes naive questions! I have been using Dave Jones' blog which is very informative. Thanks again. 

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