Solar Powered LED Blinds Group 28: Austin Estes and Kerr Oliva TA: Katherine O’Kane

Introduction The solar powered LED blinds provides a less costly method of allowing a consumer to harvest the sun’s energy. The solar panels on the blinds are directed towards the sun by a microcontroller and electric motor. A battery, which is charged by the solar panels, provides power to the microcontroller, electric motor, and RGB LEDs.

Objectives 1. Allow user to determine color of ten RGB LEDs to add an accent light to a room during the night 2. Automate blind rotation through use of a motor for the best solar power production 3. Power the system through a Li-Ion battery charged by solar panels

System Overview Hardware Solar panel array Charge controller circuit Rechargeable battery Microcontroller Motor driver LED circuit Software Microcontroller programmed to turn the blinds and turn the LEDs on and off at the correct frequency

Block Diagram: Power Solar Panels Charge ControllerLi-ion Battery Motor Driver Microcontroller RGB LEDs Electric Motor Transistor Current Mirror (BJT) Voltage Regulation

Block Diagram: Signals Photoresistor Microcontroller Motor Driver User Inputs Transistor Current Mirror (BJT)

Review of Original Design Solar Panel Array Original 27 panels in series of 3 with 9 parallel lines Rated for 18 V and 0.63 A (11.34 W) Cost: $ (4.95/unit) New 12 panels in series of 3 with 4 parallel lines Rated for 18 V and 0.664A ( W) Cost: $ (3.29/unit)

Review of Original Design RGB LED Circuit Original 30 RGB LEDS 1k Ω potentiometer New 10 RGB LEDS 500 Ω potentiometer

Power Circuitry Solar Panel Array Each solar panel produces 6 V and A The array produces 18 V and A Charge Controller The charge controller decreases the voltage from the solar panel array, increasing the current that is sent into the battery. Outputs 12.3 V and 1.32 A Rechargeable Battery Charging voltage of 12.6 V Rated output of 11.1 V and 5.7 A In ideal conditions, the battery would charge in 6.6 Ah/1.32 A = 5 hours

Solar Panel Array Three Solar Panels in Series Full SunLight OvercastPercent Change Series V15.21 V17.78% Series V16.57 V14.06% Series V16.24 V15.20% Series V15.43V17.71% Average Value18.92 V15.86 V16.17%

Charge Controller Circuit LT 3652 IC Programmed to have a battery float voltage of 12.3 V and charging current of 1.32 A Voltage output of charge controllerCurrent output of charge controller

Motor Driver H-Bridge Takes in select bits that decide the direction to apply current through a DC motor. Allows for the microcontroller to easily control when the motor is active and which direction the motor will turn. Current Limiter The current limiter limits the amount of current that the motor draws. This was done as a precaution in case the motor stalls, that way the motor won’t draw more current than it can handle and possibly start a fire.

SN VCC1: Chip power VCC2: Power that is output to the motor 1_2EN: Enable #A: Select bit for the output #Y #Y: Attached to either terminal of the motor, outputs VCC2 H-Bridge Chip

Current Limiter Circuit

Microcontroller and H-Bridge Testing The microcontroller’s interaction with the H-Bridge was tested first using a simple loop of outputs to make the motor turn back and forth. Next, we tested that the microcontroller would turn the motor different amounts depending on the voltage value it read from the photoresistor. While testing the photoresistor with the microcontroller and motor, we were never able to get the microcontroller to turn the motor different amounts depending on what the voltage across the photoresistor was.

RGB LED Circuit Current mirror biased to draw 0.2 A of current Addition of potentiometer allows for variation of color Powered through initial switch-transistor Enabled by an op-amp Driven by a current mirror Each color given their own current mirror to limit current

RGB LED Circuit Current mirror for red LED Current mirror for green LED Current mirror for blue LED Switch-transistor Op-amp

Transistor Measurements Switch Transistor Transistor Terminal Theoretical Voltage Measured Voltage Percent Error Base9.5 V9.32 V1.89 % Collector9.5 V9.44 V0.63 % Emitter8.8 V7.95 V9.66 % Current Mirror Transistors LEDTheoreticalMeasured Red0.2 A0.172 A Green0.2 A0.172 A Blue0.2 A0.173 A

Microcontroller Programming Switches control what the microcontroller activates Motor The microcontroller takes voltage readings from a photoresistor in order to find where the maximum light intensity is. RGB LEDs The microcontroller applies a square wave through an op-amp to a transistor in order to flash the LEDs at 60 Hz.

Microcontroller Programming Flowchart Automate Motor Signal Turn Blinds Using Motor One Direction -Check if light is increasing or decreasing -Increasing: Continue turning -Decreasing: Stop turning and check other direction LED Signal Flash LEDs Turn Blinds In Other Direction -Check if light is increasing or decreasing -Increasing: Continue turning -Decreasing: Stop turning, local max has been found Wait for 15 minutes while checking if the Automate Motor Signal has changed state High/True Low/False

Microcontroller Output We expected 5 V ± 0.25 V (5 % deviation) Multimeter measurement shows output of 4.8 V at I/O pin for LED and motor enable signals 4 % error

Successes and Challenges Fully functional RGB LED circuit working in conjunction with microcontroller Circuitry components not operating as expected (ex: switches & transistors) Motor driver circuit receiving input from microcontroller Photoresistor sampling not correctly signaling arduino Time management Debugging of subsystems took longer than anticipated Debugging of microcontroller Initial ATmega328P burned Soldering

Conclusion Our solar powered LED blinds had three main modules, the power circuit, the motor driver, and the LED circuit. We recommend using a lower voltage than 11.1 V to power the RGB LED circuit. The microcontroller’s motor programming is not completely functional and still needs debugging. The charging circuit needs to be tested fully in order to determine if it is safe to charge a Li-Ion battery.

Thank You