Subaru Legacy in-Car Screen: What Hardware?


In my last car-related post I skimmed over my DIY touchscreen replacement to the all-in-Japanese AEM/stock system that I’d ripped out. As with all things I seem to take on, what I have ended up with hasn’t been as straightforward as I thought to start with. I thought I’d stick down here a couple of the hardware options/ configurations I thought about.

Hardware

7″ Android Tablet

PRO

  • Going to be slick and fast since designed to run android
  • Touchscreen, BT, wifi, (4G ), jack for mic/sound: all that is there and ready

CONS

  • There are not actually that many decent 7″ tablets around. The Nexus 7 from a couple of years back is a good contender but second-hand ones are pretty pricey. I was not going to bring it up but I only started looking for a Nexus 7 when I broke the 7″ tablet I had…idiot.
  • I actually think any 7″ tablet is going to be too wide anyway. As you can see above, the space available for the thing is confined to the gap the two air ducts. People online using Nexus 7s have modified the ducts – I did not really want to do that. The other option is to start moving bits around in the device. I did try, see photo below, but made a complete hash of it – everything was way too delicate and my being a heavy-handed ape with the soldering skills to match meant failure was always going to be the outcome. Anyway – it was a tragedy.

What’s this? The inside of a Google Tango Tablet Development Kit that I managed to needlessly break. Would have been (nearly) perfect. Was too wide though – hence my attempt at surgery.

  • These tablets – the Nexus 7 anyway – share their USB host port with their charging port. Not an issue in itself really I don’t think – but the jacks (earphone too) are on the short side of the devices most of the time. So too big again for the gap between the ducts…so moving bits again with the same end result.

SAD NOTE: Au Revoir Tango

The tablet that died was a Google Tango Tablet Development Kit. It was a nice machine on paper but shaky software-wise. Unfortunately, Google announced the Tango project was defunct a couple of months ago and with it support for the kit. Consequently, the Android version was ‘frozen’ at a slightly unstable fork of KitKat: unstable I believe since the Tango device used an atypical NVidia Tegra processor.  Google Play Services was stuck on an old version and so updates to apps like Maps crashed non-stop. Weirdly, given it was (a) a dev device and (b) a Google device, the back door that meant you could root it (and maybe stick on a newer OS – maybe something used by the NVidia Shield) used or update Play services at least) was slammed shut in the penultimate system update, prior to support being dropped. This system update also broke the Tango Explorer 3D scanning tool app and measuring ruler app (the coolest apps there were for Tango) and Google removed them from the Google Play store. Anyway. In effect, and my justification for opening the thing up and (trying to) operate, was the device was rendered irrevocably useless anyway, by progress…Google has taken what they learnt from Tango and repackaged it as ARCore…which (of course) does not play with the Tango tablet ;( but does work on my Pixel XL 🙂

ARCore in action on any-old-Android-phone. Google is showcasing the technology in the Google Camera app.

To be honest, given its propensity to crash and it’s being stuck in 2015 software-wise, using the Tango tablet in the car would not have been ideal (and it was too wide anyway). One nice thing was is that the Tango came with a docking station which had a proper USB3.0 port on it, and the interface for this port was on the long edge of the device. Anyway, water under the bridge.

Raspberry PI 3  with Official 7″ touchscreen.

PROS

  • I had the touchscreen lying around
  • RPi has wifi and Bluetooth and 4 proper USB ports (this a big ‘for’ for using the RPi over the Android Tablet)
  • As OS is on SD card, can fiddle around with (software) system on another RPi in the house and just swap out with the one in the car when done fiddling.

CONS

  • Official 7″ screen to flippin’ big. Its got this dirty great black glass bevel around its edge that seems to serve no purpose – its just back-painted glass with no capacitance bits, or circuitry. I have since other screens that probably would have worked – but as I said, I had the official RPi one handy.
  • Raspberry Pi 3 is slow and bit shit RAM wise. Will probably need to overclock and so will need cooling fan & heatsink. RPi slow to boot-up as well.
  • The official RPi screen is only 800 x 480, not HD or HD-Ready (remember HD-Ready? That was weird right? It’s not that great a deal though since am not needing the resolution and I suspect ‘proper HD’ would put more of a toll on the RPi processor and RAM -wise.
  • Risk of corruption of file system or some other file on SD card when from turning off the car (and so power to RPi) in the middle of a write process on SD card. Would have to add some sort of shutdown-with-ignition-off system…more work. It has already happened a couple of times in the past with Raspberry Pis so I think its a ‘thing’, not something I am imagining.
  • OS: I’ll cover the pros and cons of the different OSs I looked at but it wasn’t until I discovered Emteria OS that I’d able to get Android to run nicely on a RPi, and some distro of Linux-for-RPi was going to be a bit shitty UI wise for a touchscreen application in a car.

HardKernel ODroid XU-4 with ODroid VU-7 Plus Touchscreen

ODroid XU-4 with cooling fan

This is just a bit of a placeholder for now. An enhanced Raspberry Pi model (RPi4 presumably) isn’t scheduled for 2018, and as a said above, the RPi 3 is a little slow and RAM light (for running Android). The XU-4 is another single-board computer RPi-a-like with more grunt: faster 8-core processor and more RAM, it ‘comes’ with a supported Android build, and can use eMMC as well as SD card – so faster read-write speeds, faster boots.

Perhaps an upgrade option in the future.

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