Thread: General Tablet Questions

i'm no expert, but i'm in the same boat so i'll share what i've found so far (i just ditched my car pc and now starting a tablet build)...

i think if you stick with an apple, motorola, or samsung device you'll likely be happier than with the limitations of a Kindle or off-brand device. i explained why i'm going with the XOOM as my platform in my new worklog: http://www.mp3car.com/worklogs/15515...rokee-4x4.html

you've likely got 3 options with sound output: the headphone out (not elegant with regards to wires showing), the dock/charge/usb connector (depending on device), and bluetooth. i've yet to look into what the highest quality bluetooth audio device is, hopefully some people with experience will chime in on this thread. some devices may offer a 4th option, HDMI out. if the devices sends 2 channel audio over the HDMI then you can get a cheap breakout box to pull out the audio, but if it's full surround sound then it's digitally encoded and you need a more expensive "audio extractor" device to pull the sound from the HDMI. i don't see any reason for a head unit except for FM or Sirius/XM.

i think for power, you'll at least want to run the charger off of a switched outlet. you can then use an app like Tasker or a profile manager to tell the device that it should never lock the screen or dim the backlight when charging, but when not charging to go to sleep right away (on Android anyway, not sure on iOS). then most tablets are perfectly capable of running asleep/locked for several days on their own battery power. if it's a long time between uses, you're going to need to leave some way to reach the power button though. there are some Samsung devices that actually run in a weird in-between state whenever they get external power - not quite on all the way, but there was an app or a firmware i saw once that would work with those devices to make them automatically turn on all the way whenever they received power. some Motorola phones automatically turn on when they get power, but i don't think any of their tablets work that way.

Stay clear of apple.android is the way to go .win 8 could be good tho if it came in a 7 or 8"...for all the good mods you need root access and a app ecosystem that that supports this...android checks these boxes..plus its very customizable. Pretty sure you can disable the lock screen, so when power is applied it will it goes back to where you left off.

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theksmith,

What do you mean by "switched outlet" ? ... Are you referring to a DC->AC adapter? And running an aux cable may be a sloppy choice, but I'm sure I could find a way to make it look clean...but does that provide the best sound quality (assuming I don't find a tablet that will work w. HDMI? And if I'm just going through aux, will I need a head unit? Also, how would bluetooth work? I'm assuming that's what I would need the head unit for.

Camo.b,

I'm 99% sure I'll be going Android...at a loss on what tablet to get though. So many choices. What do you mean by "ecosystem app" ? And I'm familiar with how to root, so that part won't be an issue...does Android have any stellar equalizing software that you know of? I'd be looking to run most of my music through Pandora, Spotify, and anything off my SD Card. Also, is there anything that you know of that's about 7" that supports a 64GB SD/microSD card?

Other questions...how will this tie in with my remote start? Will I need an app, or will I need to have the unit powered a certain way?

Originally Posted by lessthandan

theksmith,

What do you mean by "switched outlet" ? ... Are you referring to a DC->AC adapter? And running an aux cable may be a sloppy choice, but I'm sure I could find a way to make it look clean...but does that provide the best sound quality (assuming I don't find a tablet that will work w. HDMI? And if I'm just going through aux, will I need a head unit? Also, how would bluetooth work? I'm assuming that's what I would need the head unit for.

i meant that you should not hook the factory tablet power adapter to an always-on outlet, hook it to an outlet that is only on when the ignition is. that way you aren't running the vehicle battery down and also you can then use profiles that recognize when the tablet does/doesn't have external power to make the tablet's lock-screen behave appropriately.

i don't know what will provide the best sound quality for you. i haven't gotten that far yet myself. i don't think you need a head unit for anything since you already have an amp, you can just hook the tablet output (whether it's the headphone jack, hdmi, or bluetooth adapter) to the amp. you may need an adapter depending on which output you use.. for example if you only have RCA inputs on your amp, then you might need a level converter if you were using the headphone output so that you aren't over-driving the amp inputs.

search the forums for bluetooth adapters, i know other people have already solved the sound output problem and know which adapters work well... but the mp3car forums seem dead for a while now - is there another forum for this scene, or is there just no-one doing this stuff anymore?

Originally Posted by lessthandan

1) How are most people powering them? Am I just going to keep it connected to my DC jack the entire time? If so, is that wrecking my battery?

Should be able to wire it into the ignition so it charges while you're driving. The tablet will stay powered on when the car is stopped, but you put the screen to sleep until you start the car again.

Originally Posted by lessthandan

2) Do I need a separate head unit? If so, what is the purpose of having one?

You don't a seperate head unit, you could run it straight to the amp. I have a bluetooth head unit though, lets me do steering wheel controls. If you're an audiophile bluetooth may not be good enough, might have to go for hdmi?

Originally Posted by lessthandan

4) Is there one tablet that is superior to another? I'm unsure as to whether or not I'd go Android, iPad Mini, or Kindle Fire. I mean, I do know technical and general differences between the three, but...I just wasn't sure if there was a "right" or "wrong" interface to pick. Note: the most important part of all of this is sound quality!

I vote for android but apple can do almost as much as android devices (except widgets), just have to do more hacking with apple. and I've heard apple don't skimp on their sound reproduction, but some of the better android devices may be up to par.

Originally Posted by lessthandan

5) Is there a general tablet FAQ somewhere on these forums that I overlooked? I saw a few in the Projects section, but couldn't seem to find what I was looking for...

Shameless plug for my build in my sig (problly not much of a how-to tho..) there's not much to figure out for the tablet, most of them come with everything built in (wifi, gps, touchscreen, frontend etc.) Pretty much hook it into the power, and then tell it to power on the screen when there's power, sleep when there's none (Tasker for android, jailbreak for apple), then get the audio to a headunit or amp, using the headphone jack, bluetooth or hdmi. Then mount it somewhere.

Originally Posted by theksmith

but the mp3car forums seem dead for a while now

over 2000 people logged in atm, so it looks pretty busy, might just be a lot of lurking/research going on...

Power-wise the tablet will be negligible if the engine is running.

It may also be low enough to last overnight if not charging (ie, engine not running).
And old ROT (rule of thumb) or theory I used to use was that the average car battery should at least last overnight with (say) the dome light left on. That assumes a 10W domelight and many are smaller - ie, 5W. And LED lights take even less - usually well under 1W.


And you can hereby ignore the rest below. I got carried away and assumed you want to run the tablet off the car's battery when the engine is off.
But I'll leave it FWIW. Maybe just find the bold bits and see if that's of interest...


Power is V * A, ie, Volts times Amps. If your tablet's supply is 12V @ 1A, then that's 12V x 1A = 12W, though that 1A might reflect the MAXIMUM your tablet should take and hence won't be indicative of its average power, it may only be 12V @ 0.4A =~5W.
Also the (say) 1A or 400mA etc plugpack supply is likely to be the next common size suitable for the tablet. IE if it only requires 0.8A or 0.25A, they probably won't make a special 800mA or 250mA plug pack for it if they have or can get 1A or 400mA plugpacks etc.

Why mention that? Because the tablet's supplied charger or the tablet's DC jack rating should be the MAX possible demand. Hence if your battery or system can handle that, you shouldn't have any worries. In practice it should be even better, at least until your battery ages!


I'm back, sorry for that delay...
I just checked my 10" tablet's PSU. It's 5V @ 2,000mA = 3V @ 2A = 5V x 2A = 10W, the same as my above theoretical or ROT dome light. (What a nice coincidence! And of course tablet supplies are 5V... d'oh!) I wonder of that 2A sizing means my tablet consumes a max of 1.1A?

[ Ignore: Its AC input is 100-240VAC @ 0.35A which means a max of 100V x 0.35A = 35W. Ok, so that's a bad double-check. That 0.35A is its peak input current which is probably its initial peak surge current and irrelevant to typical power usage. Else it has a pf of ~0.5, but let's just forget all about that input rating... I was hoping to show its inefficiency... ]

An extra consideration is the efficiency of the tablet's PSU. For typical SMPS aka Switched-Mode Power Supply's, efficiencies are typically 80% and above, hence a 10W output means up to 10W/0.8 = 12.5W input. But that is essentially insignificant; 12.5W isn't much different to 10W and we are applying guesswork to a highly variable battery situation.
(However the inefficiency may affect our wiring & fuse choice. EG - the 10W supply suggests a 1A wire (or larger) with a 1A fuse. But 12.5W means more than 1A, hence a 2A wire & 2A fuse etc. NOTE - the fuse must always be equal or smaller than the wire it is protecting, eg a 2A fuse into a 5A or 10A cable is fine, but NOT a 5A fuse into a 2A cable, or 10A fuse into a 5A cable etc.)

Alas I can't find any DC rating for my tablet.
Keep in mind the tablet's PSU is designed to handle the operation AND recharging of a tablet's flat battery. Hence again, the tablet will consume far less power on average - ie, when its internal battery is nearly or fully charged.

A design paraphrasing of the above is to design (dimension) the electrics for the tablet's max loading, but that may (does...) not reflect its actual average power consumption.

And hence with systems of this type and small consumption, many choose the suck it and see approach. (Like hey man, even though I can do detailed battery capacity calcs etc, the reality may be VERY different. Maybe the device takes far less, or the battery is too old or too cold etc.)
To be safe, I'd suggest you have a jumper battery handy or test-start before your cohabitants leave in their cars, or have a battery charger etc.

And BTW, the above assume typical modern SPMS converters as almost always supplied to phone PSUs and car charges etc.
If a "linear" converter is used (eg, an LM317 or 7805 etc), then input power is significantly higher. EG, for a 5V 10W load, a switching SMPS converter will consume about 12-13W input whereas a linear converter will consume over 25W (~twice as much).


Many install a second battery for their tablets etc so that they have cranking battery independence. That can be to ensure cranking, but can also be so that car cranking etc does not interrupt the tablet supply, though with tablets & laptops with internal batteries, that's usually not an issue - it's more for those with PCs or big audio amplifiers etc.
BTW, those 2nd batteries need to have a battery isolator - google "oldspark uibi" and optionally "site:www.mp3car.com" to find my multitude of related posts).

In addition or even alternatively you could use a low voltage cut out or "battery protector" (like the ~$20 MW728) to protect whichever battery, though some like the MW728 have a load of ~10mA when off (ie, after the load has been disconnected). That's equivalent to a LED - ie, ~0.12W = 120mW which may be insignificant, but it is still a load on a low voltage battery, though should be insignificant compared to other loads like car alarms and (remote) central locking systems (usually about a Watt or higher).
I often recommend an extra relay that disconnects the MW728 when it disconnect the load. Though that too adds a load, it disconnects the MW728 and has the benefit of preventing subsequent cycles of reconnect, disconnect, reconnect etc that many such devices can exhibit.


Sorry for assuming you want tablet power when the engine is not running and hence the above verbose considerations. But in a nutshell, just try it. If you have battery reserve problems, then the above should provide suitable solutions.


As to a dc-ac inverter to supply the tablet's ac PSU, I'd suggest NO except as a backup or if used with the engine running an not too long when not (running).
Otherwise get a suitable automotive 12V convertor. The inefficiency of a typical inverter for such a small load is simply to high.


I've had way too many interruptions during this reply. No way is it going to flow or read well!