Specifications

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connect our own to them. The MPPT charge controllers will help regulate the power
output and will ensure that it stays within safe levels for the battery. This information will
also be fed into the same microcontroller as the second power input source.
Next, we will need to know the amount of power being drawn between all of our
devices. This would include such things as the laptop, the projector, the LCD display,
and any microcontrollers used. Since MSP430 microcontrollers are known for their low
power usage, their power usage is negligible. The rest of the components, however,
will need to be hooked up to sensors and their power usage fed into the microcontroller.
With all of this information, we will be able to calculate the total power usage of the
system. If the energy coming in from our power sources is greater than the power being
used by our components, then we will be storing energy in the battery and the LCD will
reflect this. If, however, we are not drawing in as much energy as we are using, our
system will be draining the battery. This will also need to be displayed on our LCD
screen, as well as an estimation of how much longer the battery can power the
components until it runs out of energy.
The power calculations can all be programmed on one microcontroller. The data can be
taken in, and the microcontroller can do all of the arithmetic operations required in real
time. This information can then be used to determine what action the LCD will take to
output the proper display to the user.
In order to calculate the power being used, the voltage at the load and the current going
to the load must be measured. In order to do this, the battery voltage must be scaled
down to a voltage readable by the microcontroller, which is -0.3V to Vcc+0.3V. This can
be done with a simple voltage divider placed on the PCB. In this case we will be using a
Vcc of 3.5V, so the range will be from -0.3V to 3.8V. This means we need to drop our
maximum voltage of 13.1V to 3.8V, so R1 should be equal to 2KΩ and R2 should be
equal to 723Ω. This circuit can be viewed in the figure below. The circuit below can be
included on the PCB created for the microcontrollers, or may be on a separate PCB,
depending on final board sizing requirements.
Battery Positive
Battery Negative
2KΩ
723Ω
Battery Voltage to Microcontroller
Figure 57 - Voltage Divider to Feed Battery Voltage to Microcontroller
The current going to the load will be calculated using a Hall Effect Sensor. Since there
will need to be multiple of these sensors, they will be placed on their own circuit board.