sexta-feira, 15 de julho de 2011

Power consumption

We come back today to talk about the current consumption of the clock, first noting that the following values may still not be definitive, because the project is still not completed, that is, there's still the possibility of changes in both components and on the way to link them. 
As the three buttons don’t consume too much when tight and basically nothing when not being used (just what the capacitor absorb), let's disregard the amount of current that they pull.
Then left over to do the calculations the following components: the LMs, LCD, R1, MSP, pot, and the HT1380.
Querying the datasheets (, you can get details of current drawn by each components (except R1, which should be calculated).

The values are the following: 
LM 7805
Potenciômetro + LCD

    An important detail is in the pot, the LCD pulls itself 45mA for your backlight, and a value much lower for the rest, the pot function is precisely to prevent the LCD pull so much current.

Then when everything is ready the clock will have two modes, one in which the backligth this bound (potentiometer at minimum), and the other in which they can see what this written on the LCD (pot limit).
Then to the current calculations we will consider that the potentiometer and the LCD as a single component that can consume from 0 to 45 mA.
With this we have a consumption ranging from 8281.2 to 53281.2 µA.
For the calculation of the duration of battery let's round consumption as 8.3 – 53.3 µA.
A problem to determine the running time is the fact that the storage capacity of current batteries varies widely, rapidly searched and can find batteries ranging from 170-300 mAh.

Doing the calculations for a stack of 200 mAh battery would have an approximate length of 3.75-12:0 am.
I.e. could last from one day up to a few hours if you forget the LCD turned on. For sure a duration really small for a watch, I believe that nobody is willing to change the battery of the clock once per day.
            The measure to withdraw the LM7805 in would save 8 mA, what would you change the duration time for 151-666 h. what changes of 1 day for almost a month, ok still isn't much, but already greatly improves. But the best solution would even use the recorder's input to plug an external source adapted 5V which would not use the voltage regulator, reducing consumption.


So today that’s it, we are still discussing the best solution to our problem, and come back next week with another post.

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