[Android Head-Units] Mervin The Paranoid:
Summary of my experience (with both CarPlay dongle and This Thread) and asking for some advice at the end:

Links

I only read the first and last 10-15 pages of this forum but found many good pieces of information. One very many people are asking for, and not finding (or not going back 10/ 15/ 20 pages--can't blame them) is links. Someone kindly provided this linkto the entire version history of both app and dongle firmware. Bookmark it!

Dongle and app

Recently got the wireless CarlinKit dongle (AliExpress). Latest App (29 July), dongle initially with a different firmware.

Wireless Connection Problem

[Sorted]

Two solutions: 1. External power. Used a USB hub thingy to supply external power to the dongle ( this). Not happy with it but it does supply 5v power to the dongle and connects the dongle to the tablet (I'm not using a head unit), but tablet doesn't get power, or in another configuration, tablet gets power but no data. Still it did the job of improving connection. (solution from this forum)

2. Original app was getting a bit fidgety so googled, found another AutoKit.apk on Carline.com, used that (same app actually) but it was outdated version. App asked to update both itself and the dongle; did both and dongle stopped providing wifi (worked OK with wired connection though). As someone here posted very many pages ago, pls. update firmware with a USB only. On a clean/ formatted (FAT 32) USB, copy-paste the firmware (make sure no other files). Plug dongle into Android device, open the app and plug USB into where your phone cable would normally go. A message on the app will tell you it's updating.

Also my box is plain black with no writing, markings or serial numbers on it, and I understand this is very normal. It does not have a built in mic (and I shan't need one because plan to have the box somewhere in the insides of my car eventually).

Connection

As someone on this forum, not, as I initially thought, jokingly said: allow some time to for things to settle in. I've had resolution problems, screen going blank (but still working where imaginary buttons must be), displaying a message that the "navigation machine does not support current settings", dropouts, etc. BTW for not supporting current settings, I went to "compatibility" mode, connected, played around for 10-15 mintues, then went up to the fastest mode, and it went away (a few times). But after 1 day of playing around/ trouble shooting, things have settled in very well. Note that I'm using an old tablet with Android 6.0 and 2GB RAM (also tested it on two Android phones, and when things were very bad with the tablet, it worked fine with both phones: one running Android 7 on 3GB RAM but the other Android Kitkat on, maybe 2 (but I feel 1 GB) RAM. Difference between tablet and phone was power: USB in phone was supplying more power than the tablet, and my fancy hub is a bit flimsy on the insides (despite fancy flashing LEDs in 4 colours, flat ribbon cables, price tag and all).

Voltage Testing

: I don't have the USB hub so carefully touched a couple of sewing needles on both end connectors of USB and read voltage with multi-meter. can't remember the exact figures but phones were outputting noticeably more voltage than the tab. Also this is how I know my posh Remax Aliens hub is crap (I also used the pin method with data connectors, but I don't know how much voltage to expect, and if it changes with the amount of data. I won't suggest doing this with sewing needles as there's a much greater chance of unintentionally shorting the connectors (power connectors being on the outside edges are easier).

Now I have no serious problem on my Lenovo Tab. Until about 6 hours ago, I'd occasionally get the 'not compatible message' but not any more (almost continuous testing, many connects and disconnects). Speed is a slight issue with wireless connection though. There's a very slight lag between pressing GUI button and the app opening (noticeable only if you're comparing it to how quickly it opens on your phone). But in music, there's a

two second

lag between, say pause and play buttons. Also scrubbing is not possible. I listened to a 2.15 hour long audio book streamed through carplay onto my app without any other problem than an app crash some hour or more into things. The audio (with some music and many background noises) was as clear as my tab's little speakers allow; no hiss, no dropouts, no lag. But keep in mind this is not proper music (didn't test that for more than 3 or 4 songs -- all good -- so can't say for sure). This all on latest (29 July) app and box firmware.

In short, patience seems to be the key. I didn't know electronics, especially computers needed setting-in time, but apparently this one does!

Key Mapping. There are a few questions without much clarity on this. The app clearly says it's "BETA", so don't despair too much if things don't work perfectly. Hopefully with some feedback the developers will improve on it (already quite impressed with the rate of updates and how numerous problems seem to have been solved as apparent from this forum). As I'm not going down the headunit path (BTW, usually wary of contractions, I've figured out HU stands for head unit but what's this AA everyone seems to be talking about?! BTW is slightly more universal though :), I can't speak for steering buttons, but in my one of my Aliexpress spending spree (I try to restrict it around to 1 or 2 dollars usually), got this a while ago. Works somewhat with key-mapping. two keys: up and down are, it seems, already mapped to "answer/ next" and "hang up/ back" keys; others I could map, but no long-presses. I do have to re-map everytime I open the app (or maybe after rebooting the tablet). I can't unmap the two mapped keys, and as my little contraption also automatically does commands on the tablet (e.g. going forward and backwards in the CarPlay menu, I get volume going up and down), it'll take me time to figure the whole thing out and forbid it from bothering my tablet.

As for steering buttons, I understand that in the early days, there was no set standard, but since 2010 or so, most cars follow one or two standards. It might be worth checking out if your car's steering buttons follow any of the popular standards, because if they do, sooner or later you'll be able to map the keys, but if not, look for alternatives--and yes, indeed, they do cost a lot.

My Setup (still incomplete and need advice)

I intend to put a 10 inch tablet in my dad's car, all plugged in and ready to receive his phone when he steps in without him having to interfere (not a tech fan, but loves his iphone, even when driving!) and sort of automatically go into hands-free, still with Apple GUI (which he deems the most user friendly, and knowing his aversion for technology, I have to agree). I intend to:

1. Plug the tablet in his trusty old(-ish) car's CD slot (yes AliExpress still sells those phone/ tablet fixer thingies which plug into CD slots rather than suction-on-winscreen stuff).

2. Have the tablet AND the dongle powered by concealed cable drawn from behind the headunit (2 DIN but with cassette and CD player--Andriod "HUs" didn't appeal to me, and this is still a better setup (or should be) than a cheap android HU or a very expensive Alpine with CarPlay). This is where I need the suggestions: I'll take a cable form the cigarette lighter plug and bring it from behind the console, solder a step-down board to bring voltage to 5, and then... I was hoping my super fancy 3 USB + OTG hub will do the job, but no. Waiting for a y-cable simpler OTG Hub but afraid I might be let down also, so went through Wikipedia and Google and got a plan to solder some cables together to serve the purpose of 1) supplying power to both tablet and the dongle and 2) connecting the dongle to the tablet.

Advice needed

.

1. The step down board (Aliexpress) seems to be good to also protect from over/ under current, and heat-sinked, I believe it'll not burn itself out. But should I instead dismantle a QC3 cigarette lighter adapter and fuse its innards to my power supply cable instead? Which would be more stable.

Asking because I know in older cars, cigarette lighter plugs receive inordinately high voltage at startup, causing many adaptors to burn out if I don't take them out of the socket before starting the car. Dad used to go through an average of an adapter a month, but the newer, costlier QC 2/ QC 3 adaptor I got him a 6 months ago have held out fine making me believe the circuits can now handle over voltage.

2. Y-cable or OTG hub in link above. Will it? I can't buy it from my local electronic places, so ordered it from China; decided instead of a y-cable to go for one more USB port (possibly audio out), but unsure if I should wait a couple of weeks or make my own? If my own, some advice fusing number 5 pin with +ve power supply; and of those some, a few also recommend having a resistor in line. Is this necessary?

3. Mic/ stereo setup. This is slightly more technical for me than the y-cable bit. I haven't tested it out yet, but I have two possibilities: a) the "y-cable" is actually a W or well... has one male micro, two female regulars and a female micro. I was wondering if a usb-3.5 mm contraption like this will work? The other possibility is y-plug for regular headphone jack.

I'm going to route a Boya lavalier (or lapel) mic above the A-column or up to the sun-visor or behind the steering wheel (whichever seems better after testing). So far so good. I hope this mic performs well; couldn't shell out money for a stereo/ noise cancellation mic, but dad has a keen sense of how well he's being heard and doesn't already trust the best handsfrees we got for testing (including a Parrot which I like, but indeed transmitted sound wasn't as good as from iPhone)

But for speakers, I'd like to keep two options. 1. Car stereo through aux port (straight forward but requires dad switching on the stereo and going to aux--something he might not be happy doing knowing I'm trying to restrict his telephone use during driving) and 2. tablet's speakers. Also if he's alone, he can use car stereo for phone calls but with other people, it's probably nice to use the tablet's speakers. How to do it? As soon as I plug anything (even a slitter) into the tablet's headphone jack, the speakers stop transmitting the sound. It's not intelligent enough to detect that only a mic has been plugged in. In earlier (simpler) androids, after a bit of rooting, one could force the phone to play audio both from its own speakers and from the headphone jack, but I doubt if this would be possible in newer ones. Any advice/ hack/ link?

Tablet specs

. Persistance seems to have paid off on my old Lenovo tab but since I want this to be a seamless, automated experience for my dad, wondering if the hardware's good enough. The Lenovo is a Tab 2 A10-70F with 2GB RAM, originally Android Ice-Cream Sandwich, upgraded to 6.0 (Marshmallow?). Sounds pretty decent but I'm a bit wary with initial hiccups.

I also have an older Motorola Xoom MZ 604 with 1GB RAM which originally came with Android 0 (must have been honeycomb because there's a honeycomb pattern across its back) and now running half-decently on Jelly Bean (4.something). Half-decently because unlike Lenovo it's 32 bit and doesn't support many of the newer apps. CarPlay dongle connects and works. Unlike Lenovo, it doesn't need external power. Problems however are: a) works fine on compatible mode but on fluent and speed modes (great names BTW for slow, medium, fast), it only always shows a blank screen (unlike Lenovo which is only sometimes blank) but imaginary buttons do work; and b) ONLY when Siri is activated (either with long press home button or by opening phone, messages and whatsapp), it disconnects. It doesn't matter if it's powered or not. I had a look at its memory consumption: stays pretty solid between 44 and 46MB when connected, and by activiating Siri, it doesn't shoot up; stays at 46 and says "restarting" (in "running" tab under apps--went there through car button, and activated Siri from phone) . Should I be persistent, and maybe this will work? Keep in mind, I won't be needing the tab for almost anything other than CarPlay; maybe a simple GUI interface with music stored in tab and perhaps a gyroscope/ inclinometer thing (lenovo, I just discovered doesn't have half as many sensors as the Motorola; it relies on accelerometer to interpret movement), and maybe an OBD interface and Torque.

I feel whatever disconnect-due-to-Siri problem on this specific tab (and since it'd been gathering dust for years, I factory-reset it, most of the apps, etc.) might also be cause for others when they have repeated drop outs (not due to Siri though). I did play music for half hour or so without any connection or stutter/ lag problem (except, of course, in compatible/ slow mode, the entire GUI lags 2-3 seconds behind the phone). I also feel somehow these two problems (disconnect on Siri which is specific to this tab only and blank screen which happened on both tabs, and with a few other people in these forums) should be sorted with persistance and updates (although I still find persistence to be illogical in computer context).

Or should I sell both and buy a third with more power (3GB RAM, lets say and perhaps 8") and be sure of a truly seamless experience?

And I'm sure most of you are asking why all this complication when I could simply buy a head unit. But that would be far to simple and no fun at all.