Tablet PC as Carputer?

[utc_pyro]

 

The dash is getting stupid hot as well, so I’m not sure how much removing the back of the case is going to help. But others aren’t having near the issue I am, so I’ll try cutting the center part of the case out first. Car has tint, and there is already a heat sync poking out the back of the case. Problem is thermal radiation coming through the windshield and baking it.

 

If that doesn’t work I’ll do the battery elimination mod with a supercapacitor and ultra efficient power supply. The stock battery charging circuit can manage the supercap, and the power supply would only need to handle keeping the thing alive while off.

 

Still need to change the temperature limits on the battery somehow though, because even without the cell in there you need to temperature sensor to keep things happy.

Edited May 27, 2018 by utc_pyro

[nevets27]

When going down the path of the no battery mod there is some info about the battery tempature sensor. I don't remember it all off hand but at least one way I saw it done was to retain the sensor which looks to be on a little board sitting in top of the battery. Now I'm not sure if someone successfully removed that board and just fed 5v (approximately) into the wiring going to the main board.

 

The no battery mod I remember they guy removed the battery off the little board and soldered right to where the leads came off the battery.

 

Either way, I think the temp sensor is just a thermistor and is likely just one or 2 of the few wires that go to the board. Because of course only 2 are actually power. So you should be able to just spoof whatever tempature you want via resistance.

 

You could also try to put a bit more insulation to the bottom side of the dash (top side if we are inside the dash) to try and keep the heat from soaking inside the dash. Not sure what you would use or how you would apply it though.

 

The heat sink would only help if the chips (cpu/gpu) are overheating and shutting down. If it's the battery that's causing the shut down and the chips are fine the the no battery mod would likely be enough.

 

I just have this thing for cooling all electronics as much as possible so I've modded everything I've owned with better cooling...

 

Oh and I thinking I read some people have issues with tablet not sleeping. I think the solution is that the "battery" PSU needs to be something like 4.7v and the "charging" PSU needs to be like 5.1v. I think it needs a minium of a 0.3v difference to go into a "charging/external power applied" state so it knows to wake up/go to sleep with ACC power.

 

Like to see what you come up with. I couldn't decide what I wanted to use for a psu so one of the reasons my progress has been slow. I know there are a ton on ebay but I was trying to nice but also cheap ones.

[utc_pyro]

 

Back on Solidxsnake’s ElementalX build, and I can confirm that PEM is installable. Getting it to do anything is another story though... At least LTE is working again.

 

https://forum.xda-developers.com/nexus-7-2013/development/rom-usb-host-based-rr-timur-s-t3659332

 

This is the other ROM where they were trying to graft Timur’s work into 7.1.2. Any of you android dev pros able to figure out what they had to do to make PEM work? I can see some changes to timer management, USB-OTG, and drivers for a bunch of capture cards and such but nothing that stands out as a hook for PEM to tie into.

 

Re:overheating - Ordered a 5.4v 250F super cap today to replace the battery. I can foresee Android getting pissy about a 100mah equivalent battery but this should handle transients better than just a dc-dc power supply.

 

Next is to figure out the standby supply. I want something that I can set at 4.2v, and consume less than 10 ma of power on its own. I can find these in standard stepdown supplies, but not isolated ones. Is isolation needed on this?

Edited May 30, 2018 by utc_pyro
Spelling errors

[nevets27]

 

Re:overheating - Ordered a 5.4v 250F super cap today to replace the battery. I can foresee Android getting pissy about a 100mah equivalent battery but this should handle traniants better than just a dc-dc power supply.

 

Next is to figure out the standby supply. I want something that I can set at 4.2v, and consume less than 10 ma of power on its own. I can find these in standard stepdaughter sn supplies, but not isolated ones. Is isolation needed on this?

 

The super cap is a nice idea, no one mentioned using one in any of the documentation/guides I saw. The traninats is exactly what I worried about with powering the nexus directly off a dc PSU rather then a battery. Though it that didn't seem to bother some who have done it. Still bothers me though.

 

I spent so much time trying to find decent quality, reasonable sized and efficient dc-dc it drive me nuts to the point I haven't bothered buying one which has slowed my build progress a bit.

 

I was interested in finding one with low noise but I only know enough about electronics to get into trouble so I know switching Hz was important but so was something else I can't remember off the top of my head. I was reading specs sheets for the chips. Which was the other half of the battle, figuring out what chips are being use and the common ones etc. This is all ebay based of course.

 

I do know if you go isolated that the efficiency is definitely lower I this generally mid 80%. Non isolated, switching generally is around 95%. But changes a bit on how close you are to what the chip was designed for. So if you get a 5a psu (real 5a not made up China spec'd higher then it really is) and only draw 2a it looses its efficiency.

 

So it's a compromise as you'll want likely something with at least 2a output as its likely the tablet can draw that much or close to it. You also don't want the PSU to be running at its limit so 3 or 4amp seems about right. Except when the tablet is sleeping, it will be then using much less and likely not at the most efficient rate of the psu.

 

Also could use a voltage regulator type of dc-dc psu, no noise but also inefficient.

 

Maybe I'm over analyzing it but well, that's what I do.

 

I could post what info I found on available psu's, on ebay, if anyone is interested. It's just research I did.

 

I had planned on running 1 5v psu for all my 5v stuff but I think I decided against that. My main worry was introducing noise into the audio and or just dirty power to all the 5v electronics and therefore was at first looking at a high quality isolated psu and only really wanted one but with enough power to power everything which became a challenge and had some cons. Likely overly paranoid so a more realistic aproved is probably a few smaller PSU's.

 

Oh yeah and btw, as far as I know android determines how full the battery is based off voltage. I don't even think it knows the true capacity so I doubt it will care about it being 100mah. In our case we need the voltage to be bellow what a 100% battery would be or it won't request power from the usb charger and therefore won't turn on when power is applied (car is started). So we need to make the tablet think the battery is at like 80% all of the time so that it wants to charge. I assume you knew that anyway as you said you want to set it at 4.2v, which sounds right. This is all just what I've read, no first hand experience thus far.

[solidxsnake]

I can see some changes to timer management, USB-OTG, and drivers for a bunch of capture cards and such but nothing that stands out as a hook for PEM to tie into.

 

 

That indicates to me that anything that PEM is doing is in its code (in the .apk) and is happening in user-space, and not in the kernel. Which means it should be able to work entirely with any other kernel. Don't think that code is published, though.

 

 

Re:overheating - Ordered a 5.4v 250F super cap today to replace the battery. I can foresee Android getting pissy about a 100mah equivalent battery but this should handle transients better than just a dc-dc power supply.

 

Next is to figure out the standby supply. I want something that I can set at 4.2v, and consume less than 10 ma of power on its own. I can find these in standard stepdaughter sn supplies, but not isolated ones. Is isolation needed on this?

 

 

How do you figure? A good DC supply should have no problem handling transients either. Android doesn't care about battery capacity, there's no physical way for it to determine that. There's only 3 wires to the battery: the + and -, and then a temperature sensor to prevent overcharging/overheating. Like pretty much any other Li-Ion circuit, the tablet measures battery charge by measuring the voltage. Anything above 3.7V should register close to 100%. While charging, I think it should be closer to 4.1V.

 

 

Isolation isn't necessary, but if you want clean audio, I'd highly recommend it. I built my own flyback supply, good for 5V, ~2A, and safely can handle a car's full range of battery voltages (11-15V or so). See here and here.

 

 

nevets27: I don't see why you care about efficiency of the PSU? It's not like you're restricted by the car battery or charging circuit.

[utc_pyro]

That indicates to me that anything that PEM is doing is in its code (in the .apk) and is happening in user-space, and not in the kernel. Which means it should be able to work entirely with any other kernel. Don't think that code is published, though.

 

For the most part I think you're correct, but it looks like it relies on some sort of trigger for the power state. Plugging/unplugging power isn't causing it to do anything even installed as a system app. The triggers it's looking for appear to be somewhere in the ROM code that was actually published. I just couldn't find it (not that I knew what to look for). The rom I linked to above apparently made that work, but his repo is kind of a mess and I cant figure out what changes he made.

 

How do you figure? A good DC supply should have no problem handling transients either.

 

Phones/tablets pull more current from their batteries than you probably expect. Burst loading can be quite high due to race to sleep. This is why we had the big apple battery throttling hoopla a few months ago, older batteries couldn't handle the burst current and so they had to throttle the phones to keep below that limit.

 

Android doesn't care about battery capacity, there's no physical way for it to determine that. There's only 3 wires to the battery: the + and -, and then a temperature sensor to prevent overcharging/overheating. Like pretty much any other Li-Ion circuit, the tablet measures battery charge by measuring the voltage. Anything above 3.7V should register close to 100%. While charging, I think it should be closer to 4.1V.

 

Isolation isn't necessary, but if you want clean audio, I'd highly recommend it.

 

 

This is a little more complex than just cell voltage unfortunately. That may be what the display is based on, but there is another component. The battery has a TI BQ27541 "Fuel Gauge" chip inside. That guy is hooked up via I2C to the main board, and supplies information like battery temperature, battery capacity, batty charge state (as in current going in vs out), battery life, cycle count, ect. It has a pretty accurate coulomb meter as part of it, and can thus measure how much power the battery is storing. It's little mind is going to be blown when it expects a 14220 coulomb Li-Ion battery but is only hooked up to a 250 coulomb capacitor.

 

Isolation isn't a concern for audio ground loops because I'm connecting via bluetooth. It IS a concern due to screwing up the charging circuit.

 

Based on this, I guess the first question is if the "PACK-" pin is at the same potential as the ground pin of the USB OTG connection. If so, that provides a path to go non-isolated power.

 

The next question is how does android deal with it's battery gauge information being screwed with? If it's shutdown/charge logic is based purely off voltage this may not be an issue, but it it relies on that information for anything else that might cause issues. The best case may be to inject power at "PACK+", and let the fuel gauge think it's just getting charged by the tablet. But if it gets angry because it isn't seeing a current draw then you'd be forced to inject at the cell pads. That gets into the ground isolation issues again, because it measures current on the ground side of things. You'll be getting funny ground loops through that coulumb counter, really causing the thing to loose it's mind.

 

nevets27: I don't see why you care about efficiency of the PSU? It's not like you're restricted by the car battery or charging circuit.

 

I'n not nevetes27, but in my case I care about efficiency because I don't drive for up to a week at a time. This means my car battery is rarely fully charged, and the discharge while off matters a lot. Some of the isolated DC-DC supplies I found used 45ma while unloaded (!!!). I have a few non-isolated ones on hand that are in the range of uA. Efficiency while the car is running is less of a concern, but I have the main 12v-5V regulator powering the tablet then anyway.

[solidxsnake]

For the most part I think you're correct, but it looks like it relies on some sort of trigger for the power state. Plugging/unplugging power isn't causing it to do anything even installed as a system app. The triggers it's looking for appear to be somewhere in the ROM code that was actually published. I just couldn't find it (not that I knew what to look for). The rom I linked to above apparently made that work, but his repo is kind of a mess and I cant figure out what changes he made.

 

 

The triggers are likely the ones setting the usbhost variables in the sysfs files (/sys/kernel/usbhost). That's all in the usbhost.c (or .h? i don't remember exactly) and the msm-otg.c files.

 

 

Phones/tablets pull more current from their batteries than you probably expect. Burst loading can be quite high due to race to sleep. This is why we had the big apple battery throttling hoopla a few months ago, older batteries couldn't handle the burst current and so they had to throttle the phones to keep below that limit.

 

 

Right, but my point is that a properly-designed power supply should not have any issues with burst loading. I'd wager a good PSU will be much more capable than a li-ion cell when it comes to dealing with large transients.

 

 

 

 

This is a little more complex than just cell voltage unfortunately. That may be what the display is based on, but there is another component. The battery has a TI BQ27541 "Fuel Gauge" chip inside. That guy is hooked up via I2C to the main board, and supplies information like battery temperature, battery capacity, batty charge state (as in current going in vs out), battery life, cycle count, ect. It has a pretty accurate coulomb meter as part of it, and can thus measure how much power the battery is storing. It's little mind is going to be blown when it expects a 14220 coulomb Li-Ion battery but is only hooked up to a 250 coulomb capacitor.

 

 

Ah, forgot that BQ27541 was on the battery board. Honestly? The easiest way is probably to just spoof the data the N7 wants to see by sending it fabricated data over I2C. Not sure how much security (if any) there is there. I would wager it shouldn't actually be that hard if you look at the BQ27541 datasheet and the drivers in the flo/deb kernel.

 

 

Isolation isn't a concern for audio ground loops because I'm connecting via bluetooth. It IS a concern due to screwing up the charging circuit.

 

 

Based on this, I guess the first question is if the "PACK-" pin is at the same potential as the ground pin of the USB OTG connection. If so, that provides a path to go non-isolated power.

 

The next question is how does android deal with it's battery gauge information being screwed with? If it's shutdown/charge logic is based purely off voltage this may not be an issue, but it it relies on that information for anything else that might cause issues. The best case may be to inject power at "PACK+", and let the fuel gauge think it's just getting charged by the tablet. But if it gets angry because it isn't seeing a current draw then you'd be forced to inject at the cell pads. That gets into the ground isolation issues again, because it measures current on the ground side of things. You'll be getting funny ground loops through that coulumb counter, really causing the thing to loose it's mind.

 

 

I'm fairly certain the battery (-) is connected to the USB GND, but easy to check by just using a multimeter. All of the battery gauge stuff, to my knowledge, is fed directly from the BQ27541. You can do some more digging looking at the driver in the flo/deb kernel (bq27541.c, etc). I'm willing to bet if you spoof the comms and just send the tablet some nominal values, everything will work out just fine.

 

 

I'n not nevetes27, but in my case I care about efficiency because I don't drive for up to a week at a time. This means my car battery is rarely fully charged, and the discharge while off matters a lot. Some of the isolated DC-DC supplies I found used 45ma while unloaded (!!!). I have a few non-isolated ones on hand that are in the range of uA. Efficiency while the car is running is less of a concern, but I have the main 12v-5V regulator powering the tablet then anyway.

 

 

I suppose if you're running battery-less, then yeah, that's an issue. Forgot you guys were looking at battery-less operation.

[utc_pyro]

Ok, the driver rabbit hole seems to point toward what makes PEM work. It looks like a lot of it is related to changes he made in the drivers. The charging driver is putting out more state notifications than the stock one. There are also several other (i think event managers?) that seem to be publishing additional information.

 

https://github.com/androdev88/flo/commit/ee3cc530e5644378f06d50747acc77d1b5f29ee1#diff-22db095f5fedc04c2fd5ce2a3fc146c3

 

I never realized how much Timur changed to make his kernal operable... Now the questions is what Dev can I bribe to merge just the power related parts of this back with ElementalX

 

Also looking at the bq27541 drivers, it doesn't look like it is checking the security stuff that chip CAN do. So that means your idea of spoofing it looks viable. That opens up some neat opportunities like having the tablet auto shut down if the car battery gets low.

Edited May 30, 2018 by utc_pyro

[solidxsnake]

Ok, the driver rabbit hole seems to point toward what makes PEM work. It looks like a lot of it is related to changes he made in the drivers. The charging driver is putting out more state notifications than the stock one. There are also several other (i think event managers?) that seem to be publishing additional information.

 

https://github.com/androdev88/flo/commit/ee3cc530e5644378f06d50747acc77d1b5f29ee1#diff-22db095f5fedc04c2fd5ce2a3fc146c3

 

I never realized how much Timur changed to make his kernal operable... Now the questions is what Dev can I bribe to merge just the power related parts of this back with ElementalX

 

Also looking at the bq27541 drivers, it doesn't look like it is checking the security stuff that chip CAN do. So that means your idea of spoofing it looks viable. That opens up some neat opportunities like having the tablet auto shut down if the car battery gets low.

 

 

I already have a work-bench set-up to compile Elemental-X, so merge the changes and add a pull-request on my github and I'll compile it for you, if you want. I'll push my latest changes to my github account in a little bit: https://github.com/solidxsnake/flo/

[nevets27]

BTW the no battery thing kind of got started by Kevdav100.

 

 

So it's been done. And many followed after that. I don't know how good/nice his mod is but just pointing out that the people less concerned "just did it"

 

And yea I'm with utc_pyro right now, the car sits sometimes and this isn't the only additonal power draw accessory thats been added. So the least amount of draw will help prevent a dead battery and honestly car batteries don't like deep charge cycles either.

 

BTW I would like to hear what ends up being that quality PSU we are speaking about. I found that hard to find. I mean quality and reasonably priced. The cheap ones are dirt cheap.

 

Also I'm not sure if it's just my tablet/12v-5v adapter or what but when looking in PEM, with GPS and music streaming I'm not chargein I'm actually loosing power slowly. So I'm not sure how that would would with the no battery mod. If using a lower current PSU for the battery and a more powerful PSU for the "charging" would the tablet be ok with trying to draw more power through the battery then the usb.

 

I have tested the adapter and cable and it's capable of far more current then the nexus is asking for.

[solidxsnake]

BTW I would like to hear what ends up being that quality PSU we are speaking about. I found that hard to find. I mean quality and reasonably priced. The cheap ones are dirt cheap.

 

 

https://www.adafruit.com/product/1385

 

 

That's a dirt-cheap supply that sacrifices performance for form-factor. Assume worst-case efficiency of 75% across the board (which is a severe underestimate), and if the tablet's in deep-sleep (let's assume 10mA draw, which is a severe overestimate given my experience), that comes out to roughly a 5mA draw on the battery side (assuming 5V output, 12V input). Non-isolated, though, so that's potentially undesirable. If you want an isolated supply, you'll probably have to build it yourself, which is why I did exactly that

[utc_pyro]

I ended up ripping the usb port off my Nexus 7 while working on it, so pulled it apart early to fix it. USB ID pin pad came off, so I'm going to refactor the whole thing with dedicated usb host, usb client client, and charge ports.

 

On battery removal: "PACK-" is infact the same ground as USB. So it's OK to inject power on the tablet side of the battery back with a non-isolated supply. The thermistor isn't immediately apparent on the battery board and a lot of it is covered on epoxy, so spoofing is starting to look even better.

Edited May 31, 2018 by utc_pyro

[xt2005bonbon]

fwiw, my 05 stays in the garage easily for a whole week without turning the engine on. After a week, the tablet only lost like a couple of % of charge. Timur ROM/Lollipop. And my car battery is 6 years old now .

Zero 'hacks'/mods done to my nexus set up. I am just using a 'cheap' 12-5V DC-DC supply.

The only thing I'd like to do at this point is get rid of the noise in my audio. Noticeable at low volume. Quite annoying.

[solidxsnake]

fwiw, my 05 stays in the garage easily for a whole week without turning the engine on. After a week, the tablet only lost like a couple of % of charge. Timur ROM/Lollipop. And my car battery is 6 years old now .

Zero 'hacks'/mods done to my nexus set up. I am just using a 'cheap' 12-5V DC-DC supply.

Yeah, mine is about the same amount of drop. After a week I was in the 93% range or so. But we still have our batteries, so when the car's off, the tablet setup is completely disconnected from the car battery. These guys are looking into battery-less operation, which would require using the car battery full-time.

 

 

The only thing I'd like to do at this point is get rid of the noise in my audio. Noticeable at low volume. Quite annoying.

Sounds like you need to build yourself an isolated supply

[xt2005bonbon]

Sounds like you need to build yourself an isolated supply

 

I know I know. Too many projects right now ...

On the battery subject though, I installed a 35 Ah AGM battery in my trunk (Kinetik audio HC800 BLU), because I bought a ........ fridge

[nevets27]

I ended up ripping the usb port off my Nexus 7 while working on it, so pulled it apart early to fix it. USB ID pin pad came off, so I'm going to refactor the whole thing with dedicated usb host, usb client client, and charge ports.

 

That sounds familiar. The seller I got it from didn't mention it had a messed up port. So I had to replace it and when trying to take the old one off i pulled two of the pads off. Should have known better. Had to run some solid wire from a couple solder points close to the port. Pain in the ass but got it working. I had the same thought and was going to hard wire everything to the the pcb and run the wires out the back to a board with power, usb host etc. Like you're doing. But I'm thinking longer term I might end up with something other then the nexus so I rather not "destroy" it. The nexus is already pretty old and a bit slow. Not sure what to replace it with though yet. Going to use the nexus as a starting point though.

 

I know I know. Too many projects right now ...

On the battery subject though, I installed a 35 Ah AGM battery in my trunk (Kinetik audio HC800 BLU), because I bought a ........ fridge

 

Glad to know I'm not the only crazy one. I was looking to do something similar. I just want something to keep a few bottles of water cold. More info!

[xt2005bonbon]

Glad to know I'm not the only crazy one. I was looking to do something similar. I just want something to keep a few bottles of water cold. More info!

 

 

After lots and lots of research and given the trunk space we have, I opted with a drawer type fridge. It is a 30L fridge (Dometic CD-030) which is not bad at all for a family of 4. We went on a 2 night camping trips and we did not have to go to the store to buy more stuff. It was so nice. Not cheap though. But keep in mind that they have a smaller version (20L) which is about half the price. Next project is relocate the battery in the underfloor storage tray.

 

 

 

 

 

Not mine but you get the idea:

 

 

[ame=http://www.youtube.com/watch?v=PlBIvQPcH2k]Waeco cd-30 draw fridge - YouTube[/ame]

[utc_pyro]

 

First thing on interest is the 10K NTC thermistor circled in red. Per the drivers, valid temperature range is -20C to 80C. You won’t ever get that high though, there is a 77*C circuit breaker in the battery pack that will trip out first. The charging circuit drivers want this value to be 0-40C for normal charging, and it has a low voltage mode between 40-45C. One will want to replace this with a 10K resistor.

 

The next area of interest is the voltage based protection circuit in green. As it’s covered in epoxy I can’t see what voltages it will trip out on, but we can get an idea from the drivers again. Charging circuit will read 4.5V to 3V as valid values, and has over-voltage recovery above 4.3V. That points to likely cutoff voltages at 3v and 4.5v. Several other onboard components (SOC especially) have an upper limit of 4.5v, so bypassing this and delivering straight 5V like people were doing is a bad idea.

 

Finally there is the 0.075 current measurement resistor circled in blue. If you want to bypass the voltage protection though, the “top” pin from this can be taken over to the “PACK-“ output of the board.

 

So my current plan is to use a MP1584 buck converter on the PACK+/- pins set to 4V. It has a 100uA quiescent current and efficiency in the mid 80%’s, so shouldn’t add to car battery drain.

 

The supercap will go on the cell +/- pins and be charged by the stock logic. It’d probably run just fine with only the MP1584 (~4A burst current), but it puts out ~50mv of noise though so having it shut down while the table is powered is probably a good thing. If the tablet out draws the USB port the caps will sag to 4.0V and the external supply will take over again.

 

Edit: Can confirm that this worked even without the super cap.. Can also confirm my tablet is forever dead due to the ripped usb port. Had to order another 5 year old tablet today. :spin:

Edited June 2, 2018 by utc_pyro

[utc_pyro]

Ok, found a way to make Solidxsnakes’s ElementalX kernal work cleanly.

 

[ame=http://www.youtube.com/watch?v=QeC_Sd6xg7w]How to install an Android tablet and control it in your car - YouTube[/ame]

 

LineageOS 14.1 + OTG patched ElementalX + Xposed Framework + Xposed Edge Pro

 

It dosen’t have the nice startup/shutdown animation, but it’s FAST and feels OEM like. Need more testing to see if USB is as stable as Timors kernal, but this looks promising.

 

On the battery replacement thing: 4V dc-dc converter hooked up in parallel with battery has been working fine on my bench over the last few days. Battery sinks to the fixed voltage (below the safe float voltage of the pack) and just sticks. Plug power in and the built in charger takes over.

 

This worked well enough one could consider just relocating the battery lower in the dash, but I wouldn’t be comfortable doing that without a fully functioning temperature sensor. Standard lithium ion batteries really don’t like being charged below freezing, and extended temp ranges ones done have the same chemistry and thus voltage profile.

 

SuperCap should be here tomorrow. Not optimistic about it’s capacity (they don’t even make a 500F greencap), but it should be a nice stable battery simulator to keep all the logic happy.

[solidxsnake]

Might need to look in to this. If it speeds up the airplane mode transition, then I'm definitely looking into it!

[utc_pyro]

There is a slight delay in triggering (~1sec), but it steps through everything almost instantly. Airplane mode transition is as fast or faster than PEM, you can barely see it happen.

[utc_pyro]

Super capacitor got here, started experimenting.

 

 

Good news: It works, and the stock charger will charge it.

 

Bad news: As expected though the BQ27541 is being a pain in the ass. It doesn't really realize that the "battery" capacity is 3% of what it was originally. This manifest itself in it thinking the battery is stuck between 78-81%, and doesn't auto shutdown. I've considered changing the current measurement resistor to 3ohms so the capacitor capacity and OG battery capacity match. Unfortunately the BQ27541's current measurement maxes out around 3A, so it would again be loosing it's mind.

 

So this leaves reprograming it, or building a custom battery simulator. TI has tools to do the former, but they are dependent on if the OEM locked it down. Building a battery simulator would be the most robust, but I'd need something to use off the shelf that supports the Arduino IDE and will do 1.8v I2C. Obviously it's possible (and fun) to design a board to do this as one could integrate the standby charger and even car battery voltage but requires more time than I have.

Edited June 16, 2018 by utc_pyro

[utc_pyro]

“Production” tablet rebuilt and Reinstalled in the bezel. Going to try this setup on Solidxsnake’s ElementalX kernal with XposedEdge automation. SuperCap battery replacement seems stable, so staying with that.

 

[ame=http://www.youtube.com/watch?v=UosfPeVnGe4]Legacy GT Nexus 7 Dash Install - Magnetic Button Control - YouTube[/ame]

 

 

Added reed switches for the power and volume buttons so they can be controls with the tablet in dash. Just need to use a magnet.

 

 

Also Apple CarPlay works well on a Nexus7

 

[ame=http://www.youtube.com/watch?v=Y5sGn-0OXCQ]Carplay on Nexus 7 - YouTube[/ame]

Edited June 29, 2018 by utc_pyro

[solidxsnake]

The reed switches are a pretty sweet touch!

 

Is that hot glue holding the tablet up? I can almost guarantee you that will fail if you run the heating. Yes, even the high-temp stuff.

[utc_pyro]

The reed switches are a pretty sweet touch!

 

Is that hot glue holding the tablet up? I can almost guarantee you that will fail if you run the heating. Yes, even the high-temp stuff.

 

Hot glue was just used to “tack” it in place before I put the Sugru on. Then it was used on the tablet side of two of the L-brackets. I couldn’t get enough force for the tape to fully stick doing it in two directions. Those are just to provide a more solid feel, there is enough Sugru that it’s not going anywhere.