Milestone 4.1

4.1: Optimization

The first prototype had many ways it could be optimized. They've been categorized and explained below.

Case (housing) Optimization:

  • Phone buttons didn't work on the original prototype, as there were no cutouts.

  • The case did not provide a tight fit around the corners. It also didn't have any overhang to hold the phone in when turned upside down, as it was made out of a rigid plastic.

  • The case was too thick around the camera, obstructing the 0.5x zoom camera.

Electrical Optimization:

  • The early prototype did not allow for a wide range of input voltages from the solar panel. We noticed the voltage output from the solar panel varied with light intensity, so allowing for lower voltages would allow the solar panel to provide power in lower lighting situations.

  • On/off switch was inaccessible in the case, so charging couldn't be turned off

Display Optimization:

  • The early prototype did not display the battery life or solar power input as expected.

  • Display also did not have an external on/off button

We did the following to optimize these weak areas of the early prototype.

Case (housing) Optimization:

  • Cutouts and soft plastic buttons were added where necessary.

  • Adjusted the radius of the corners. Changed material to a soft plastic to allow for a tight fit around the phone and an overhang over the front of the phone so it doesn't unexpectedly come out of the case.

  • Design was modified so both rear cameras are unobstructed, which also required a thinner display.

Electrical Optimization:

  • Various buck-boost controllers were tested to lower the minimum output voltage from the solar panel and still have it supply 5 V to the usb port. Testing showed under fair indoor lighting conditions, the output voltage averaged around 2 V.

  • The desired buck-boost converter with an input range of 1.5 V to 6.5 V did not work as expected, as it would not work with a load connected.

  • The next best buck-boost converter with an input range of 3 V to 16 V did work, allowing for a wider input range of voltages from the solar panel than the previous voltage regulator with a range of 5 V to 8 V.

  • External on/off toggle button was added to control output (charging) power

  • An additional charge controller was added and modified to limit max current draw, preventing the power supply (solar panel) from being overloaded.

Display Optimization:

  • The battery life and solar power output are now displayed as expected

  • Display and charging power was also given an external on/off toggle button

GREEN CASE