Difference between revisions of "S13: Solar Panel Tracker"

Revision as of 03:39, 22 May 2013

Grading Criteria

Project Title

Abstract

The objective of this project is to create a solar panel that tracks the sun. The project will consist of two stepper motors that control the position of the solar panels by using the photo resistors to detect the sun location.

Objectives & Introduction

Solar Panel Sun tracker uses the inputted voltage from photo resistors in order to adjust the position of the solar panel. The project uses and Analog to digital converter. The servo motors are controlled using a pulse; this controls the position of various angles. The servo uses in this project is a standard servo which can only position between 0 and 180 degrees.

The project required the following objectives to be accomplished:

• Read the voltage from photo resistors
• Control servo to move from 0 to 180 degrees
• Compute the location which has the greatest light intensity
• Determine algorithm to convert digital value into servo position

Team Members & Responsibilities

• Arturo Montoya
  • Light Sensors (PWM driver) , Servo motor(ADC driver) , and Matrix (Spi driver)
• Matthew Balhorn
  • FreeRTOS Software Design

Schedule

Parts List & Cost

Design & Implementation

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Hardware Design

Light Sensor

The Solar Panel Sun Tracker consists of the following hardware:

• Resistors
• Photo resistors

This section is responsible for interpreting the voltage of the photo resistors. The diagram below shows the circuit needed in order to get a voltage division of the two photo resistors. This voltage divider consists of two resistors on each side of the voltage divider output (ADC pin). When the top photo resistor has a greater resistance then the bottom resistor the voltage output will drop. When they both have the same resistance will hold in the middle.

Servo Motor

The servo section consists of the following hardware:

• Servo Motors / Servo Belts
• Solar Panel

This section is responsible for positioning the solar panels perpendicular to the light source. The panel is mounted to a frame that pivots according to the top servo. In order to perform a full scan the top servo motor was mounted on pivoting bases that is controlled by the second motor. The diagram below describes the complete setup in order to properly track the sun from sun rise to sun set.

Hardware Interface

PWM

PWM, or Pulse Width Modulation, was used to control the two 180 degree positional servos. The servos required a 50 Hz (20 ms) duty cycle, and the duration of the high duty cycle (in milliseconds) would control the position to move to. Typically, the valid high duty cycles are between 1.0 and 2.0 milliseconds, with 1.0 representing '0 degrees', 1.5 representing '90 degrees' and 2.0 representing '180 degrees.' However, we found that the valid duty cycle range was larger, ranging from [INSERT FULL RANGE]. Knowing this, we expanded the range of the duty cycle and converted the range into a degree range with the change_direction_with_Degree() function. The servos were connected to a 5V power supply and were controlled by PWM1-4(P1.23)and PWM1-5(P1.24).

ADC

Software Design

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Implementation

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Light sensor Logic

The LightSensors.cpp file contains the functions that the Light-sensing task calls. These functions are getDirection(), which reads the referenced Analog-to-Digital Converter pin (ADC-4 or ADC-5), and returns a value which is the new change in direction for the respective servo motor (Top or Base). The getDirection() function reads the ADC pin value and uses it to decide which direction the servo should move towards, and returns either a positive degreeChange, a negative degreeChange, or a 0 for no change. For this project, we decided to use 5 degrees as the degree change. The getDirection() function can be seen below:

Servo motor Logic

The ServoMotors.cpp file contains the change_direction_withDegree() function, which updates the PWM Match Register for the given PWM signal and the degree. This function takes the degree value, ensures that it is within range, then converts it into milliseconds so it can be written to the respective Match Register, using the PWMUpdateMR() function defined in the PWM driver file. We used the definitions Max_degree, Servo_Width, Servo_Start, and freq_ms, whose values may need to be changed if a different servo motor is used. Max_degree is the farthest degree available to the servo motor (180), freq_ms is the duty cycle (20 ms), and the Servo_Width and Servo_Start are derived from the duty cycle thresholds (in ms) mapped to the degree range (0 - 180) of the servo motor.

Light-sensing Task

The Light-sensing task was very simple. To keep it this way, all of the 'heavy lifting' was completed in lower level code in the LightSensors.cpp file. Therefore, the only function that the Light-sensing task needs to use is the getDirection() function. However, there is a small amount of code to prevent the degree values from going out of range (0-180 degrees). The task reads the getDirection() values for both the top and base servo motors, which have valid values of negative five (-5), zero (0), or positive five (5). These values are added to the current positional value to obtain updated values to pass to the Servo Motor task through the Queue.

Servo Task

The Servo Task is even simpler. It takes the top and base positional values from the Queue, then passes the value to the servo motors using the change_direction_withDegree() function, which is defined in the ServoMotors.cpp file.

Testing & Technical Challenges

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Wifi Connection Issues

Many wifi connection issues were encountered. To solve this problem, a dedicated task was created to re-connect to wifi if the connection was ever lost.

Conclusion

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Project Video

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Project Source Code

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References

Acknowledgement

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References Used

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Appendix

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