The Quest for (always-on) Power
A part of the challenge when planning the Android head unit build was finding the best way to power the development board in the car. One area that tablets and smart phones have an advantage over a development board like the ODROID-X2 is that they come with a battery. This means that not only can the be powered by something as simple as a 12v car plug, but also that there's some level of power remaining after the vehicle ignition stops.
As mentioned in previous posts, my choice to provide a stable power output to the 5 volt 2 amp ODROID-X2 is the Minibox intelligent DC/DC converter. The Minibox device can be configured to provide the 5 volts the X2 needs, as well as the 12v a standard Lilliput touchscreen requires. While this device can provide the power the development board demands during a drive, there's no easy way to notify the ODROID-X2 that the ignition signal is off and the board needs to shut down gracefully. A quick search on Amazon presented me an opportunity to potentially never have to shutdown, effectively creating an always-on solution for the ODROID-X2.
The Anker Astro E4 is an external power source specifically designed to recharge tablets and smart phones. It provides a mammoth 13000mAh, enough juice to completely recharge a Samsung Galaxy S3 twice over and then some. The new plan given the E4's specs is simple. Instead of the Minibox DC/DC powering the ODROID-X2 directly, it will instead charge the external battery pack. The battery back will then serve a constant dose of 5 volt power to the ODROID-X2. Using the all too valuable android app Tasker, I can set the development board into a low power state, stopping all non-critical processes and turning the WIFI and GPS devices off. Tasker can automate this task based on my phone disconnecting from the Bluetooth connection the ODROID-X2 creates upon startup, then automatically restore the power state upon Bluetooth reconnection.
The key to the planned implementation of the battery is the real-world battery life available, a factor that I've only begun to start testing. Nevertheless, the preliminary results are very promising. With the ODROID-X2 in full power mode (no services/devices disabled), the Anker battery has been running 6 hours without 1 of the 4 charge light indicators showing a partial discharged state. If I can effectively achieve 2-3 days out of a battery charge, the always-on portion of the Android head unit build will be considered a success!
More test results soon to come, along with a video breakdown of how Tasker automates my Android install.