This document summarizes the design of a light-controlled comfort umbrella. It describes the project timeline and goals. It outlines the mechanical design including a state diagram to open and close the umbrella flap based on light levels. The electrical design uses a phototransistor to sense light levels, op-amps to convert this to a voltage, a PICAXE microcontroller, and an H-bridge motor circuit to control umbrella rotation based on the light reading. Technical challenges around oscillations are discussed and addressed.

1. Light-controlled Comfort Umbrella
Billy Byun, Marcus Cain, Lee Ferber, Rasesh Joshi

2. Table of content
• Executive Summary and Background
• Project Timeline: Goals and Tasks
• Design: State Diagram, Mechanical, and Electrical
• Light-to-Voltage: Phototransistor Circuit and Op-amps
• The Controller: PICAXE
• Voltage-to-Rotation: Motor Circuit and H-bridge
• Technological Challenges and Learning
• Conclusion, Cost, References, and NGs

3. ExecutiveSummary and Background

4. Project Timeline

5. Design: Mechanical

6. Product: Mechanical

7. Open the flap layer until 50<L<70
Design: State Diagram
• Too cold
• Little
sunlight
If L < 50
• The
'Comfort'
Zone
100< L <150
• Too hot
• Too much
sunlight
If L > 200
Close the flap layer until 50<L<70
- Four critical values in the feedback system.. Wide?
- Sensitivity vs. Oscillation (Noise)
- Hysteresis & Deadband..System with Memory
- L: Intensity of the Light under the Umbrella.. Relative !
sensitivity

8. Design: State Diagram
Phototransistor
(Light-to-
Current)
2 Op-amps
(Current-to-
Voltage & Gain)
PICAXE
H-bridge (Two
–way rotation)
Gear Motor

9. Design: Electrical

10. Light-to-Voltage:PhototransistorCircuitandOp-amps

11. Light-to-Voltage:PhototransistorCircuitandOp-amps
• Phototransistor Circuit Demonstration

12. TheController:PICAXE8M2

13. TheController:PICAXE18M2
Note: if the H-bridge connects +VDC to
R1 and GND to R2 at the same time or
+VDC to R3 and GND to R4 at the same time,
It shortens the battery. Hence..

14. Voltage-to-Rotation:Motor CircuitandH-bridge

15. Voltage-to-Rotation:H-bridge
Resistor 1 Resistor 2 Resistor 3 Resistor 4
Forward VDC VDC GND GND
Reverse GND GND VDC VDC
Halt GND GND GND GND

16. Voltage-to-Rotation:H-bridge
Motor Circuit Demonstration

17. Voltage-to-Rotation:Power-GroundBoard
• Current Divider with two 15 Ohms resistors

18. Components

19. FinalDemonstration
• http://www.youtube.com/watch?v=kHai--hbqNA&feature=g-upl

20. TechnicalChallengesandLearning
• Oscillations (H-Bridge)
Single power supply -> Capacitor and Serial in-
Ground
• Oscillations (Phototransistor Circuit) -> Wider range
• Oscillations (Noise) -> Larger Umbrella and Curtain
• Speed of the rotation: Current Divider
• Photodiode with reverse bias configuration ->
Phototransistor
• Soldering -> Debug!

21. Reference
• http://www.johnloomis.org/ece445/topics/egginc/pt_char.ht
ml
• http://www.robotroom.com/BipolarHBridge.html
• http://en.wikipedia.org/wiki/Hysteresis
• http://en.wikipedia.org/wiki/Phototransistor#Other_modes_o
f_operation

22. Take0–YoutubeNGs
• NG1 : http://youtu.be/2Ko6o740K6k
• NG2: http://youtu.be/_-qF7b6f4oU