For the interactive drum robot installation “MR-808 Interactive” we need interfaces that control this art installation. We choose Nexus 7 2013 (second version) Tablets as they are cheap (ca. 120€ at Ebay) and easy to use. On them we open a web-based drum sequencer that controls the physical moves of the robot in realtime.
KIOSK / TERMINAL MODE
There is no native “kiosk mode” for (nexus) android tablets, and thus it is hard to limit the access to the tablet when the tablets are exposed to the public. When presenting the installation, several hundred people per day are playing with the installation and are touching the interfaces. And we want the interface to show only one website (or app). Its not evil behavior that crashes the installation, but pure “I can press all the buttons at once”: Exposed WIFI settings, open camera app, and random web pages are what is exposeed if we don’t close most of the actions the tablet is capable of.
Our interface is a website running a CSS drum sequencer, which is via MIDI connected to the drum installation. You can find the github code here
The interfaces are Nexus 7 2013 tablets, which are reasonably cheap (120€ ebay price). During the development we run into several problems, which we want to describe here.
Powering a tablet which is constantly powered on
You want the tablet to be constantly on. So you plug in the power supply and you realizes: with an app constantly using WIFI, and a bright screen the tablet draws more power than the power supply can provide, so its empty after several hours.
What we found out:
- Use a strong 2A USB wall socket.
- Dim the screen to the lowest acceptable level.
- Shut down bluetooth andthelike.
We managed to keep the power consumption and input equal. Forthermore we used an app like “power manager wake look” to tell the tablet not to shut or dim down – ever. Like this the installation runs “forever”.
Here are several other things we found out:
- The Nexus 7 2012 (first edition) has a worse power management compared to the 2013 edition. They cannot be constantly powered on and cahrged at the same time without loosing power after several hours, when the tablet then shuts down.
- The tablets get a little warm but thats ok.
- We wondered if the tablet’s screen get a burn-in, when they display the same
website for a long time. This actually should not happen because Nexus Tablets have an IPS LCD Screen. But in reality they get a burn in after some time.
The tablet in kiosk mode
We had to make sure, that the users are not accessing parts of the tablet that they should not see. Its a no-brainer to wipe the tablet off all personal data before exposing it to the public.
But its hard to suppress the “home”, “back” and “app” button of the tablet.
We used a laser cut and 3D-printed frame to cover the buttons in hardware, so they can not be touched. Works perfect and holds the tablet in place as well.
When it comes to the web browser, we had the issue, that you can click on an image very long, enabling a dialog which is asking for download, which finally enables the user to break out of the browsers. We suppressed this “feature” by disabling it in CSS, please see our github code for that.
With all the modifications mentioned above, we were able to uses the nexus tablets over two years on changing exhibitions around the world.