SolarPowerChartingTool

  
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The cell we will use for our solar tracking experiment is made from crystalline silicon and has a maximum voltage rating of. 55V and a maximum current rating of 300 ma. The cell can be picked up in your local Radio Shack for about $5. Although the cell doesn`t produce much power, this experiment can certainly be scaled to handle higher wattages.
SolarPowerChartingTool - schematic

Power is the measure of energy per unit time. It can be calculated by multiplying voltage by current at the output of the solar cell. Because our GP-3 Board can only measure voltage, we`ll need to create what is called a current-to-voltage converter circuit. This circuit takes current from the photovoltaic cell and runs it through a couple of operational amplifiers to produce a corresponding voltage (1V corresponds to about 10 milliamps). Figure 2 shows the circuit constructed for measuring current from the solar cell. The operational amplifier (also known as a differential amplifier) is a great circuit for sensing or measuring just about anything because it keeps the voltage at one input at a reference point determined by the other input. The first opamp is the current-to-voltage converter. It takes the current from the photovoltaic cell and converts it to a voltage determined by the 100 ohm feedback resistor. Unfortunately the voltage produced at the output of the first opamp is negative (which the A/D channel on our GP-3 board can`t measure). We need to flip the polarity of this voltage using a second op amp set up to invert the voltage sign. This positive voltage is then fed into pin 10 of our GP-3 board, which is actually channel #0 of our A/D (Analog to Digital) converter. The charting program consists of a User Control that plots data points on an XY Plotter. (See my previous article, An XY Plotter User Control in...



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