My old HP Stream 7 can now run around the clock on external power, once I figured out I needed to disable its battery drivers. Doing so silenced the module that foiled my previous effort. (It would raise an alert: “the tablet has run far longer than the battery capacity could support” and shut things down.) Ignoring that problematic module, remaining drivers in the same large Intel chipset driver package allowed the machine to step down its power consumption. From ten watts to under two watts, even with the screen on. (Though at minimum brightness.) Quite acceptable and I’m quite certain I’ll repurpose this tablet for a project in the future. In the meantime, I wanted to jot down some notes on this hardware as reference.

The magic incantation to get into boot select menu (getting into BIOS, reinstalling operating system, and other tools) is to first shut down the tablet. While holding [Volume Down], hold [Power] until the HP logo is visible. Release power immediately or else it might trigger the “hold power for four seconds to shut off” behavior. (This is very annoying.) The boot select menu should then be visible along with on-screen touch input to navigate without a keyboard.

There are many drivers on the HP driver downloads site. Critical for optimized power consumption — and majority of onboard hardware — is the “Intel Chipset, Graphics, Camera and Audio Driver Pack”. I also installed the “”Goodix Touch Controller Driver” so the touchscreen would work, but be warned: this installer has a mix of case-sensitive and case-insensitive code which would fail with a “File Not Found” error if the directory names got mixed up. (/SWSetup/ vs /swsetup/)

The available drivers are for Windows 8 32-bit (what the machine came with) and Windows 10 32-bit (what it is successfully running now.) The machine is not able to run 64-bit operating system despite the fact its Intel Atom Z3735G CPU is 64-bit capable. I don’t know exactly what the problem is, but when I try to boot into 64-bit operating system installer (true for both Windows 10 and Ubuntu) I get the error screen

The selected boot device failed. Press <Enter> to Continue.
[Ok]

Which reminds me of another fun fact: this machine has only a single USB micro-B port. In order to use USB peripherals, we need a USB OTG adapter. Which is good enough for a bootable USB drive for operating system installation… but then I need to press [Ok] to continue! The usual answer here is to use an USB hub so I could connect both the bootable OS installer and a keyboard. There’s actually no guarantee this would work: it’s not unusual for low-level hardware boot USB to support only root-level devices and not hubs. Fortunately, this tablet supported a hub to connect multiple USB devices allowing bootable USB flash driver for operating system installation to coexist with USB input devices to navigate a setup program.

I’ll probably need some or all of these pointers the next time I dig this tablet out of my pile of hardware. For now, I return it to the pile… where I noticed an unpleasant surprise.

I gave up trying to run my HP Stream 7 tablet on external DC power with the battery unplugged. The system is built with a high level of integration and it has become unreliable and too much of a headache to try running the hardware in a configuration it was not designed for. So I plugged the battery back in and installed Windows 10 again. And this time, the Intel chipset driver package installed successfully.

This was a surprise, because I thought my driver problems were caused by hardware I damaged when I soldered wires for direct DC power. Plugging in the battery allowed these drivers to install. And the driver package is definitely doing some good, because idle power draw with screen on minimum brightness has dropped from nearly 10W to just under 2W. This is a huge improvement in power efficiency!

So I wanted the drivers for low power operation, but maybe I don’t need every driver in the package. I went into device manager to poke around and found the key to my adventure: The “Batteries” section and more importantly the “Micro ACPI-Compliant Control Method Battery” device. This must have been the driver that rendered the system unbootable once I unplugged the battery — as an integrated system, there’s no reason for the driver to account for the possibility that the user would unplug the battery!

But now that I see this guy exists, I think perhaps it is part of the mechanism that outsmarted me and was skeptical running on external power. I disabled the drivers in the “Batteries” section and rebooted. I reconnected the external power supply keeping battery at 3.7V. Disabling the battery power related drivers were the key to around-the-clock operation. With the battery device absent from the driver roster, there’s nothing to tell the system to shut down due to low battery. But since the battery hardware is present, the driver package could load and run and there’s something to buffer sharp power draws like plugging in USB hardware. This configuration was successful running for a week of continuous operation.

Drawing a modest two watts while idle, this tablet can now be used as anything from a data dashboard, to a digital picture frame, or any other project I might want to do in the future. I don’t know what it will be yet, but I want to make sure I write down a few things I don’t want to forget.

I’ve been trying to get a HP Stream 7 tablet running in a way suitable to use as a future project user interface or maybe a data dashboard. Meaning I wanted it to run on external power indefinitely even though it could not do so on USB power alone. When I supplied power directly to the battery it would shut down after some time. The current session deals with disconnecting the battery and feeding the tablet DC directly, but this machine was designed to run with a battery and it really, really wanted its battery.

While I could feed it DC power and it would power up, it would intermittently complain about its battery being very low. This must be in hardware because it would occur when booting into either Windows or a Debian distribution of Linux. This shouldn’t be an input voltage problem, as my bench power supply should be keeping it at 3.7V. But there’s something trigging this error message upon startup and I have to retry rebooting several times before operation would resume:

HP Battery Alert

The system has detected the storage capacity of the battery stated below to be very low. For optimal performance, please attach the power adapter to charge the battery over 3%, and then re-power on the unit.

Primary (internal) Battery

Currently Capacity: 2 %

System will auto-shutdown after 10 second

Perhaps my bench power supply isn’t as steady as I assume it is. Perhaps there are problems keeping up with changes in power demand and that would occasionally manifest as a dip in voltage that triggers the battery alert. Another symptom that supports the hypothesis is the fact I couldn’t use USB peripherals while running on the bench power supply. When I plug in a USB peripheral, the screen goes black and the system resets, consistent with a power brownout situation.

So to make the hardware happy and to support sudden spikes in power requirements, I really need to plug the battery back in. Trying to run without battery was a fun experiment but more importantly it gave me an idea on running this tablet on continuous external power: silence the battery driver.

My HP Stream 7 seems to be having problems with a Windows device driver, but the problematic driver is somewhere in a large bundle of Intel chipset related drivers. For another data point I thought I would try an entirely different operating system: Debian with Raspberry Pi Desktop. Also, because I thought it would be fun.

Debian with Raspberry Pi Desktop is something I encountered earlier when looking for Linux distributions that are familiar to me and built for low-end (old) PC hardware left behind by mainline Ubuntu builds or even Chrome OS. The HP Stream 7 tablet fit the bill.

One amusing note is that since HP Stream 7 is formally a tablet, the default resolution is portrait-mode which means taller than it is wide. Unlike the Windows installer which knew to keep to the middle of the screen, the Debian installer scaled to fit the entire screen making for some very difficult to read tall narrow text.

Once up and running, the Debian with Raspberry Pi desktop ran on this tablet much as Raspberry Pi runs its Raspberry Pi OS, except this configuration is comparable to a fresh installation of Windows: many devices didn’t have drivers for proper function. I disabled Secure Boot in order to access non-mainline device drivers, which is thankfully straightforward unlike some other PCs of the era I had played with. But even then, many drivers were missing. Video and WiFi worked, but sound did not. A pleasant surprise was that the touchscreen worked as input, but only at the default orientation. If I rotate the desktop, the touchscreen did not adjust to fit. And while an idle Debian drew less power (~8W) than plain vanilla Windows (~10W) it is still significantly worse than this tablet running at its best.

Seeing Debian with Raspberry Pi Desktop run on this tablet was an amusing detour and possibly an option to keep in mind for the future. On the upside, at no point did Debian complain that the battery is low, because the operating system didn’t think there was a battery at all. The hardware, however, really misses the battery’s absence.

I disconnected the battery on my HP Stream 7 tablet and soldered wires to put power on its voltage supply lines. The good news is that the tablet would start up, the bad news is that Windows couldn’t complete its boot sequence and gets stuck in a reboot loop. After a few loops, Windows notices something is wrong and attempted to perform startup repair. It couldn’t fix the problem.

My first thought was that I had damaged a component with my soldering. A small tablet has tiny components and I could have easily overheated something. But portions of the computer is apparently still running, because I could still access the Windows recovery console and boot into safe mode. But I didn’t have any idea on what to do to fix it while in safe mode.

Since there were no data of consequence on this tablet, I decided to perform a clean installation of Windows. If it succeeds, I have a baseline from which to work from. If it fails, perhaps the failure symptoms will give me more data points to diagnose. A few hours later (this is not a fast machine) I was up and running on Windows 10 21H2. Basic functionality seemed fine, which was encouraging, but it also meant the machine was running in unoptimized mode. The most unfortunate consequence is that the tablet runs hot. The power supply indicates the tablet is constantly drawing nearly 10 Watts, no matter if the CPU is busy or idle. A basic Windows installation doesn’t know how to put machine into a more power efficient mode, putting me on a search for drivers.

Since the tablet is quite old by now (Wikipedia says it launched in 2014) I was not optimistic, but I was pleasantly surprised to find that HP still maintains a driver download page for this device. Running down the list looking for an Intel chipset driver, I found a bundled deal in the “Intel Chipset, Graphics, Camera and Audio Driver Pack“. It sounded promising… but during installation of this driver pack, the tablet screen went black. When I turned it back on, the dreaded reboot loop returned. Something in this large package of Windows drivers is the culprit. Maybe I could try a different operating system instead?

While spending way too much time enjoying the game Hardspace: Shipbreaker, I was actually reminded of a project. In the game, safely depowering a ship’s computers involve learning which power systems are on board and disconnecting them without electrocuting yourself. It got me thinking about my old HP Stream 7 tablet that couldn’t run indefinitely on USB power and refused to believe an illusion of free energy when I supplied power on the lithium-ion battery cell. I thought it might be interesting to see what would happen if I disconnected the battery and supplied DC power directly.

My hypothesis is that the earlier experiment was foiled by the battery management PCB, it was too smart for its own good and realized the tablet had consumed far more capacity than its attached battery cell had any business providing and shutting the computer down. By disconnecting that PCB, perhaps the doubting voice would be silenced.

To test this idea, I would need to find the power supply and ground planes on the circuit board. I could solder directly to the empty battery connector, but that would make it impossible to plug the battery back in and was too drastic for my experiment. I could see pads underneath the connector clearly labeled VBAT + and – but I couldn’t realistically solder to them without damaging the connector either.

Taking my multi-meter, I started probing components near that battery connector for promising candidates. The search didn’t take long — the closest component had pads that connected to the voltage planes I wanted. I had hoped to find a decoupling capacitor nearby, but this doesn’t look like a capacitor. With a visible line on one side, it looks like a diode connected the “wrong” way. Perhaps this protects the tablet from reverse voltage: if VBAT +/- were reversed, this diode would happily short and burn out the battery in the interest of protecting the tablet.

Whatever its actual purpose, it serves my need providing a place to solder wires where I can put 3.7V (nominal voltage for single lithium-polymer battery cell) to power the tablet while its original battery is unplugged.

Good news: The machine powers up!

Bad news: Windows doesn’t boot anymore!

I could see the machine boot screen with the HP logo, and I could see the swirling dots of Windows starting up. But a few seconds later, the screen goes blank. We return to the HP logo, and the process repeats. Time to diagnose this reboot cycle.

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UPDATE: Comment by Craig pointed to this project, which directly soldered 5V supply not to the mainboard but to the battery management circuit board (without battery.) https://www.instructables.com/Run-HP-Stream-7-Tablet-Without-a-Battery/

After salvaging the LED backlight from a Chunghwa CLAA133UA01 display panel, I have processed all the disembodied panels in my hardware stack. But I still have plenty of other displays still embodied in some type of hardware of varying levels of usefulness. The least useful item in the pile is my HP Stream 7 Windows tablet. For reasons I don’t understand, it doesn’t want to charge its battery while it is up and running. It seems the only way to charge the battery is to plug it in while it is powered off.

If I wanted to use this tablet as portable electronics as originally intended, this is annoying but workable. But there’s not much this old tablet could do that my phone (which has grown nearly as large…) can’t do, so I wanted to use it as a display. But if it can’t charge while running, and it can’t run without its battery, then it’s not going to be useful as an always-on display. After poking around its internals, I set the tablet aside in case I have ideas later.

It is now later! And here is the idea: if I can’t convince the tablet to charge its battery while running, perhaps I can do the charging myself. I peeled back some protective plastic to expose the battery management circuit board, and soldered a JST-RCY compatible power connector(*) in parallel with the lithium-polymer battery cell.

Putting this idea to the test, I first ran the tablet until the battery voltage dropped to 3.7V, the nominal voltage for a LiPo battery cell. I then connected my benchtop power supply to this newly soldered connector. The power supply was adjusted to deliver a steady 3.7V. In theory this means the battery would drain no further, and all power for the tablet would be supplied by my bench power supply.

To test longevity, I turned off all power-saving functions so the tablet would not turn off the screen or try to go to sleep. The tablet was content to run in this condition for many hours, and after the first day I was optimistic it would be happy to run indefinitely. Unfortunately, this budget tablet was smart enough to notice something was wrong. I’m not sure how it knew, but it definitely refused to believe the illusion its battery is an endless source of energy. Despite the fact that battery voltage was held steady at 3.7V, on-screen battery percentage started dropping after about forty hours. Eventually the indicated charge dropped below 10% and entered battery-saver mode, followed by shutting itself down. Despite the fact its battery voltage was held at 3.7V, this tablet acted as if the battery has been depleted.

After the failure of this test, I contemplated pulling it apart and extract the tablet backlight as I did to a broken Amazon Fire tablet. But I decided against doing anything destructive, and I put it aside yet again hoping to think of something else later. In the meantime I switch gears from this digital tablet to an analog glass tube TV.

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(*) Disclosure: As an Amazon Associate I earn from qualifying purchases.

I wanted to see if I can employ my unused HP Stream 7 as an International Space Station tracker at home, displaying ESA’s HTML application. The software side looks promising, but I ran into problems on the hardware side. Specifically, power management on this little tablet currently seems to be broken.

The first hint something was awry is the battery runtime remaining estimate. It is unrealistically optimistic as shown in the screen image above: 46% battery may run this little tablet for several hours, but there’s no way it would last 4 days 4 hours. At first I didn’t think it was a big deal. Battery-powered devices that I’ve dusted off would frequently give wildly inaccurate initial readings on battery. It is common for power management module to require a few charge-discharge cycles to re-calibrate.

In the case of my tablet, a few battery cycles did not help. Battery estimates remained wildly inaccurate after multiple cycles. But I was willing to ignore that estimate, since battery life is not a concern in a project that intends to run tethered to power around the clock. The bigger problem was the tablet’s behavior when plugged in.

Once power is plugged in, the battery life estimate disappears and (plugged in) was added to the description. This is fine, but I had expected to see something about charging the battery and there was nothing. Not “charging”, not “2 hours until full”, not even the occasionally infuriating “not charging”. There is a complete lack of information about charging in any form.

Still I wasn’t worried: if the tablet wants to run off plug-in power and not charge the battery, that’s fine by me. In fact I am happy to leave the battery at around 50% charge, as that is the healthiest level for long term storage of a lithium chemistry battery. But that’s not the case, either: the tablet will run mostly on plug-in power, but still slowly drain the battery until it was near empty, at which time the tablet would power down.

Only after shutting down did this tablet begin to charge its battery. Now I am worried. If I can’t run this tablet on plug-in power alone, requiring a battery that can’t be charged while it is turned on, that combination would make it impossible to build an around-the-clock ISS tracker display.

What I wanted to do next was to poke around with the hardware of this tablet and see if I can run it without the battery. Fortunately, unlikely most modern compact electronics, the HP Stream 7 can be opened up for a look.