1 of 13

Technology Implementation and Challenges

2 of 13

The Experiment. Why?

  • Never been done before
  • Only way to learn if it can be done is to do it
    • Would hardware survive?
    • Would kids figure out how to use them?
    • Would they stay engaged?
    • How much solar is needed?

​

3 of 13

Which Tablet?

  • Evaluated several tablets
    • Ease of use and Software (Android)
    • Battery Life
    • Power Draw
    • Charging Time
  • Why the Xoom?
    • Ease of use and Software were essentially equal
    • Run Time / Charging Time
      • Charges in 2.7 hours (33Wh). Runs for 7 hours
      • Others had similar run times and power usage but much longer charge times. 6-7 hours
    • Dedicated charging
      • Xoom uses 12V and custom plug rather than 5V microUSB. Help prevent cell phone charging.

4 of 13

Proposed Solar Charging Station Design

8 Tablets per station

​

​

5 of 13

Actual Solar Charging Implementation

Single Station 20 Tablets

​

​

6 of 13

Solar Performance Monitoring

  • Phocos CX charge controller with 7 days of logging. Stores various operational data. Allows for performance review.
  • Lascar UL-USB-3 Voltage monitor connected to battery sampling every 60 seconds.
  • Data files are collected once a week on the site visit.

7 of 13

8 of 13

9 of 13

10 of 13

11 of 13

Tablet Software

  • Educational videos
  • Educational apps
    • Homegrown apps (Tinkrbooks, Matching, Nell)
  • Funf sensing framework
    • Logs battery voltage & SOC%
    • Logs running applications every minute.
  • Camera snapshots every 10 minutes
  • Application launch tracker
  • Funf log data periodically moved to SD Card
    • Sneakernet over FedEx
  • App locker to keep settings from changing.

​

​

12 of 13

Challenges

  • Date reset bug "Groundhog Day"
    • RTC resets when battery is totally drained
  • Long latency between updates and results
    • Data collection only once per week.
  • Funf bugs
    • Had to disable a lot of probes that kept table awake.
  • App operation while offline
    • Many apps phone home and stop if they can't.
  • Procedural problems
    • Sneakernet over FedEx has lots of manual steps
    • Vowels in Amharic are less important
    • Duplicate data
    • TZ confusion

13 of 13

  • Large amount of pictures black or only partial views.
  • Processing and visualizing large amounts of data. 145 GiB of data.
  • Rainy season
    • 200W input good enough in Wolochete but not enough in Wonchi
  • Children don't do what you expect
    • Customized app screen layouts
    • Bypassed our application launch tracker
    • Enabled options for login screen
    • Figured out how to take pictures outside of our app

​

​