MSP430 Based Chronulator (using Launchpad chip)

Step 2 The Circuit

Below is the schematic for the Chronulator. It has 3 push buttons, two of which allow you to adjust the minutes and hours. Pushing the minute or hour buttons will increment the minute or hour values by one. The third button is a reset button. The circuit diagram shows the meter current limiting resistors that I used for my particular meters. I have a 50 uA full scale meter for my minute meter, and a 100 uA full scale meter for my hour meter. The value of the resistor installed between the meter plus terminal and the microcomputer pin depends on the full scale of the meter used.

Here is a table of what resistor you should use based on the meter FS value.
It assumes you are using the 2.5V Vcc that the author originally used.
          
                Resistor           mAh used by                   mAh used by
    FS         value         Hour meter per 12 hrs     Minute meter per 12 hrs
--------------------------------------------------------------------------------------------------
  50 uA        33k                 0.025                                    0.3                                 
100 uA        18k                 0.050                                    0.6
   1 mA       2.2k                 0.5                                        6.0

More sensitive meters are definitely better. If you have to use a FS=1mA meter
use it for your hour meter.

With the 2.5V voltage regulator you should be able to take the batteries down to about 1V and get at least 80% of the batteries' energy (~2000 mAh) without any calibration shifts.
Note: If you are using 4 AA batteries and a 3.3V voltage regulator the results are the same.

If you are using a 3.3V Vcc use these resistor values:

                   Resistor
   FS             value
-------------------------------
  50 uA            47k
100 uA            22k 
   1 mA           2.7k 



If for some reason later when we calibrate m_cal and h_cal, the sum of the elements of your m_cal array or your h_cal array are not between 8000 and 9500 adjust your resistor value. If the sum of the array is above 9500 reduce the resistor value. If is below 8000, increase the resistor value.  


 Note: The capacitor that is wired parallel to the Reset button has been changed from 0.1uF to 1nF. This change was made to make "spy-by-wire" work.    dp-09/10/10