Database Users

Battery charging in "old school mode"

I forgot the usb cable in the office and I have to charge the HD2 battery. I tried connecting the PSP charger directly to the battery blades for 30 minutes but nothing seems to have charged.
PSP Charger: 5Volt 1500A
The HD2 battery have 3 blades:
[+] [?] [-]
Did I have to use the blade in the middle as positive or negative?
Do you know anything?
Thanks

The middle one isn't needed for bare wire charging.
Just a thought but did you put + to + and - to - ? ( which you should)
Got an old mini USB cable? Use that, end off, black to - red to +,,,, and thirty minutes is about 28 minutes into the danger of explosion/damaged battery zone.

nicola853
Try to measure charging current with a simple multimeter if got one and put a 1.5 kOhm resistor in series with battery and charger. This should limit charging voltage on battery poles to regular 4..4.2V as needed for Li-ION battery charging. Seems like internal battery security circuitry detects overvoltage (above 4.3V) and cuts off charging.

Measuring battery current accurately

It's been a pending project of mine to try to accurately measure what is using the battery.
Yes, there are all kinds of numbers that you can get off the battery stats,
but to be able to see in real-time and kill/disable things is helpful.
Moreover, there is a continuing problem of Nooks not sleeping sometimes.
I'd really like to get a handle on that.
Measuring current into the USB charging port will not give you a realistic measurement.
The best way is to measure the battery current using a "battery eliminator".
That's a power supply that hooks into where the battery was.
One of the problems is hacking the battery ID and NTC thermistor so that the device will think that a battery is connected.
Here's my layout that I just got working.
Battery connector is a 6 pin JST SH from SparkFun.
I do have numbers coming off it right now.
I need to write some host software to plot a scrolling graph.

Very nice Renate! But 6-pin! Sound quite a lot, perhaps 2 pins are the same?
It would be interesting to know what gas-gauge that battery is using. I posted
something about this HERE (for a different device/battery).

The Nook pinout is:
Code:
1 red battery
2 red battery
3 yellow temperature (10K NTC thermistor to ground)
4 green ID (30K to ground)
5 black ground
6 black ground
This has been verified to the extent that the Nook won't boot up on a power supply without two resistors.
Also, I can play with the thermistor resistor and get freezing or boiling temperature.

Are you reading actual current draw through the battery, or using the power supply current along with the battery?
Parallel connections can not supply actual current draw measurements, you must be connected and read this measurement in series only. Voltage is able to be read in parallel.
Charge rate is also read through the thermistor, as a change ( or delta) of the actual current fed to the battery, and adjusted to compensate for charge level, and current capacity of the battery as a single cell.
Temperature comes into play, and this is the job of the temp probe (thermistor), and is fed back to the charge controller.
Sent from my Nexus 7 using xda app-developers app

Look, Ma, no battery!
AECRADIO said:
Are you reading actual current draw through the battery...
Click to expand...
Click to collapse
Battery? What battery?
That 6 pin plug is going in where the battery was.
At 4V, peak current at boot is around 250 mA.
Lowest idle current measured is 8 mA.

battery current/voltage
I was not suggesting there was a battery connected currently, but was curious on how current was measured.
I saw the configuration you posted, and without seeing the setup up close, the pic does not detail the method used to decipher battery current witth the setup you supplied. Power supplies do not suffer from actual current drain as the supply is always constant, and should the supply be robust enough, there should be no sag in current level over actual draw. I see why you did this, and I was simply trying to figure out the method used to measure actual battery current draw, nothing more.
Thank you for the information.

There are 3 ways to measure current.
The first is to use a current transformer, this only works with AC currents.
The second is a Hall effect sensor.
The third is the tried-and-true method of inserting as small a resistor as possible inline and measuring the voltage across it.
The resistor can be in the hot lead or the ground lead of the low.
This is referred to as high-side or low-side monitoring.
High side monitoring is more desired because you have a single "ground" voltage.
Most small DC power converters do not have accurate, accessible current measurement.
For example, a normal PC power supply can not measure the current on the 5V or 12V.
I bought the specific DC converter that I use because it offers a constant current mode and the measuring resistor was visible in the photo.
I had presumed that it was high-side monitoring because I thought they would have mentioned it in the product description if it were not.
I found out that it was low-side monitoring.
That means that the input "ground" pin is not the same as the output "ground" pin.
In fact, that small resistor is the connection between the two.
The INA219B has a differential input that goes to the measurement resistor.
It is generally used as a high-side monitor because it is designed to handle the high common mode voltages up to 26V.
Yes, you can use it to measure low-side monitoring, but then you lose the auxiliary ability to measure the supply voltage.
Since the measurement resistor goes straight across the two "grounds" I can measure the voltage at the PCB terminals instead of soldering into the measurement resistor.
Of course at the low resistances involved this adds additional resistance which must be calibrated out.
The resistor on the PC board is 0.050 ohms.
I can and will add an external 0.050 resistor on the high side to enable me to measure current and voltage simultaneously with a single INA219B.
Of course, this will add 100 mV drop to the supply at a 2 A drain.
I'll break out the voltage sense of the supply to the far end of the external resistor and that drop will be compensated for.

Current measurement.
Renate NST said:
There are 3 ways to measure current.
The first is to use a current transformer, this only works with AC currents.
The second is a Hall effect sensor.
The third is the tried-and-true method of inserting as small a resistor as possible inline and measuring the voltage across it.
The resistor can be in the hot lead or the ground lead of the low.
This is referred to as high-side or low-side monitoring.
High side monitoring is more desired because you have a single "ground" voltage.
Most small DC power converters do not have accurate, accessible current measurement.
For example, a normal PC power supply can not measure the current on the 5V or 12V.
I bought the specific DC converter that I use because it offers a constant current mode and the measuring resistor was visible in the photo.
I had presumed that it was high-side monitoring because I thought they would have mentioned it in the product description if it were not.
I found out that it was low-side monitoring.
That means that the input "ground" pin is not the same as the output "ground" pin.
In fact, that small resistor is the connection between the two.
The INA219B has a differential input that goes to the measurement resistor.
It is generally used as a high-side monitor because it is designed to handle the high common mode voltages up to 26V.
Yes, you can use it to measure low-side monitoring, but then you lose the auxiliary ability to measure the supply voltage.
Since the measurement resistor goes straight across the two "grounds" I can measure the voltage at the PCB terminals instead of soldering into the measurement resistor.
Of course at the low resistances involved this adds additional resistance which must be calibrated out.
The resistor on the PC board is 0.050 ohms.
I can and will add an external 0.050 resistor on the high side to enable me to measure current and voltage simultaneously with a single INA219B.
Of course, this will add 100 mV drop to the supply at a 2 A drain.
I'll break out the voltage sense of the supply to the far end of the external resistor and that drop will be compensated for.
Click to expand...
Click to collapse
Looking at the device's ratings, I see how you are performing the measurement, using the shunt to measure current, taking loss into consideration.
The '219B is the more precise of the two I looked at. Common-Mode rejection is good, @ 100 dB, which essentially removes the device from the circuit, and you get a more pure reading, without the inherent noise from the device while it is operating.
Differential swing is full range, and Common-Mode is normal with a reduced voltage range from -0.3 V to +26 V as you would not have a negative-leading current or voltage with a battery powered device, so the negative readings are inconsequential and of little use, unless you plan on shorting the battery to ground for some reason, or attempting to measure negative I/V.
Do your findings to date match those of the factory-defined measurements for current drain and battery life?
There are times I find manufacturer specs to be a little more lenient than accurate, but give a good, overall idea on performance while in real-time operation.
Are you able to identify the time required to charge your battery from depletion to full charge, and how long this takes?
What is your actual current draw while charging, and does the voltage change dramatically during charge, IE: +3.2 V depleted/charge begin, to +4.4 V end-of-charge state.
I hope you will post all of your findings/readings so others will understand what you have done, and why.
I am certain there are plenty of interested parties awaiting your report.
To make this a little more understandable, here's the Texas Instrument data sheet for the actual device:
http://www.ti.com/lit/ds/symlink/ina219.pdf
There are two types, with identical pins, only transposed, so one can flip one bug over on its back if necessary.

I'm still using the serial out of the ATMega32u4 right now to get the data.
I have to switch that to USB HID so that I can free up the USB com cable to use for the console monitor.
I (mostly) finished up the scrolling host GUI.
The Y scale is adjustable with mouse scroll wheel.
The X axis is 5 seconds for the minor divisions, 30 seconds for the major divisions.
Here's an interesting example from my Nook sitting idle on the launcher.
The big spikes every 60 seconds are the display updating the clock in the status bar.
The 40 mA or so square waves are a mystery.
However, the big surprise is from the left to the right side of the graph.
The device was fresh booted, the left side is showing a minimum of 95 mA.
The right side is showing a minimum of 10 mA.
That's a major difference.
What caused it to change? A ping over WiFi. (See the 4 little spikes.)
Something is clearly wrong.
This all goes to show that ps and top won't tell you where your current is going.
Edit: It's running on USB HID sensor now and in a case.

The strange 5 second 40 mA waves have been traced down, if not explained.
I'm running a console on a UART with a USB serial adapter.
Normally the dmesg comes streaming out the console.
When you hit a single key on the console, it gets eaten and a 5 second timeout begins during which 40 mA more are consumed.
If another key is hit during this time, it is actually processed by the console shell.
This also extends the 5 second timeout.
By continuously typing the 40 mA excess never times out.
Clearly there is a bug somewhere. It could be a wait loop eating CPU (and current).
So why the randomness?
The stock software has this on ttyS0, which does not have any level shifters.
I reconfigured this to be ttyS1 which has 3.3V level shifters.
If I don't have a console UART cable connected the RX in flaps in the breeze without a pullup.
Random noise causes 5 second 40 mA waves.

Could you dig out the schematics or model name of that huge buck 4V buck converter? I like it.

The CV/CC buck power supply is from eBay
The INA219B and a small SOIC8 breakout board were from DigiKey.
The 0.050 ohm resistor was from a small ebay seller.
(I can dig out the details later if you are interested.)

I scavenged some acrylic "light pipes" out of a power strip.
They are 3mm or 1/8" in diameter and about 15mm or 5/8" in length.
The have a flange that mounts with glue to the underside of the panel.
If somebody knows where I could find more of these?
They are the perfect size to route the LED lights out of the power supply.

Thank you! I am interested in the solution in general as soon I'll need to make similar measurement setup for few embedded devices. I might go with LDO converter though to maximize accuracy of power source (though the 50mv ripple doesn't seem to matter in this kind of solution THAT much, whatcha think?)
Are you planning to opensource I(t) GUI when it's ready? ; >
//edit: oh yea - LED pipes stuff http://www.mouser.com/Mobile/Optoelectronics/LED-Indication/LED-Light-Pipes/_/N-b1d20

One of the advantages to using a buck converter over a linear regulator is that you can short the output for fun.
This is a convenient way to set the current limiting.
I have a shorting plug for just such a purpose.
@Rebellos: Thanks for the hint on light pipes.
I had (wrongly) presumed that they were all custom manufactured pieces.

I got a ZTE Awe at a Black Friday price of $20 so I'm playing with that.
I made a "fake battery" out of a Radio Shack 1" x 2" x 3" project enclosure front panel.
The panel has ridges that fit the battery compartment width perfectly.
I cut the length down about 1/2".
The battery contacts are on 0.1" centers, so using a bit of perfboard as a template I drilled some holes in the cover.
I stuck a 3 pin header through the holes, glued it and soldered wires.
The central pin needed about a 47K resistor to ground to look like the thermistor.
Directly to the left (on the small photo) is a 5 hole place for factory pogo pins.
3 of the pins are a direct connect to the battery connector.
2 of the pins are running about 1.8V.
They could be contact closures or I2C or UART or who knows what.
Not enough pins for SPI or JTAG.

So one thing that I have been wondering about is the current draw from your USB audio adapter. I was specifically wanting to know the battery life while listening to music with the screen turned off. I seem to remember there being a draw of 150mA if the Nook is in host mode, period. If so, is this some sort of software inefficiency, is it contingent on the USB audio adapter, or is it something else entirely? My ultimate goal is to use the Nook heavily as an MP3 player, even if that means honing some rookie Java skills.

@t_0_0_l: Apperently the Nook is running in a tight loop.
It eats up that much current just in USB mode with nothing connected.
Getting slightly off tangent here, but this info could be useful to someone.
The mystery 2 pins on the 5 pin connector on the back of the ZTE Awe
prove to be contact closures to ground for VolumeUp and Reset.
The VolumeUp pin is directly in parallel to the side pushbutton.
Powering up the Awe with VolumeUp pressed sets it in FTM mode.

This works well if you increase battery size
Just a quick thanks for this post...
Renate NST said:
The Nook pinout is:
Code:
1 red battery
2 red battery
3 yellow temperature (10K NTC thermistor to ground)
4 green ID (30K to ground)
5 black ground
6 black ground
This has been verified to the extent that the Nook won't boot up on a power supply without two resistors.
Also, I can play with the thermistor resistor and get freezing or boiling temperature.
Click to expand...
Click to collapse
I just completed a project to root a Nook ST and convert it into a flight computer... As I'm a new user you'll just have to cut and paste vimeo.com/67223752 into your browser to see an old iteration of this in action.
Connected to the internal UART input I have used a couple of different serial GPS modules... one with a barometric sensor as well. Soldering is a bit tricky but achievable for someone with a bit of practice.
I used a "3.7v 4000mah Replacement Battery for 7'' Scroll Explore Tablet" from eBay as a replacement battery for the existing Nook ST battery, with a couple of resistors that were somewhat similar in value to the above (just what I had lying around). These were soldered inline to 'hack' the new battery so the Nook would accept it. So, with the GPS module running and software on full power/refresh mode, the Nook runs for something like 10+ hours continuously when I tested it (the unmodified version returns 4 hours). This is what you'd expect with the original battery having 1500mah. The case did need to be modified fairly extensively to fit the new 'fat' battery. Although I have no doubt that I could cook up a 3D printed back, it would require kit that I don't have to scan the existing one to a high degree of accuracy before I could mod it. So, I hacked a big chunk out of the middle of the back and then stuck a new flat plate on top of that, which provided the extra mm or so of depth needed for this fatter battery.
So, anyway, if you are thinking of fitting a huge battery to the Nook ST big thanks to Renate for this info as it works very well. The new battery does indeed charge without any issues. The only issue it seems to have with mine is that the battery percentage is a bit random (as I assume that is set in the firmware to correspond with the existing hardware). The battery I'm using has its own protection circuitry on it, so likely the Nook can't really understand what is happening. Proof of the pudding is really in the length of time you have to play with device before it gives up, and obviously with a battery this big you don't need to worry about power saving measures!!
As this project is a mix of hardware hacking and software hacking there is no one location that I can post the project to on the XDA forum as I think it falls foul of the 'no hardware' rules on the software forums and 'no hardware' on the software forums, but I suspect that there aren't many paraglider, hanglider and sailplane pilots on here for which this would be of interest anyway, but if you do want the gory detail please post up here!

Using Lipo Charger to directly power android tablet

My android tablet suddenly died on me and refuses to power up. Unable to charge the battery as well.
Am thinking of removing the battery from the tablet and then hooking up a lipo charger to the black and red wires on the circuit board. Hopefully this can power it on directly without the battery.
This is a simple and inexpensive lipo charger I'm looking at:
www[dot]sgbotic[dot]com/index.php?dispatch=products.view&product_id=999
Few concerns that I have:
Can the lipo charger be used as a direct power supply? I know voltage-wise, it's safe (3.7V). But I'm not sure if circuitry-wise, a charger works the same way as a power supply
Is 500mA current output from the charger enough to power on the tablet? If not, what is the recommended current output?
How do I know if the tablet has any logic to detect the presence of a battery? From what I see on the circuit board, there are only 2 black+red connectors (no data connector or anything)

A proper battery should less than that $15 charger. Even if you did bypass the battery you should be able to find a less expensive power supply.
Sent from my SM-N900T using Tapatalk

Spoo76 said:
A proper battery should less than that $15 charger. Even if you did bypass the battery you should be able to find a less expensive power supply.
Sent from my SM-N900T using Tapatalk
Click to expand...
Click to collapse
It uses a 12000mAh battery, which I think cost $40-60. The thing is, I'm not sure whether the issue lies with the battery. So i thought of bypassing the battery and see if it is a circuit board problem.
Here's the "tablet" I have. It's actually the viewing panel of my digital door viewer. Essentially a stripped down Android tablet:
www[dot]rollupcn.com/index.php/iHome4/show/19.html

Btw here're the pics of how the battery and the mainboard look like:
https[colon]//d3nevzfk7ii3be[dot]cloudfront.net/igi/SYJVWTdAPAPBRVCG
https[colon]//d3nevzfk7ii3be[dot]cloudfront.net/igi/q52LQk2X1s6NOaTK
Thing is - I'm not sure if the problem lies with the battery or the mainboard. Any suggestion on how to troubleshoot?

If you want to hack your Power from battery to directly input,
but fails to bypass battery check.
I have a idea that works. (some electricity knowledge required)
You can use a capacitor to "cheat" PMIC, and running on usb cable power.
Go buy a super capacitor (a 4.0F V-type should be OK.)
Charge it with the working voltage. (a few seconds is enough for that.)
Then remove your battery. Strip off the battery controller that you'll need.
Find out the positive and negative on it.(Important!)
And connect the charged super capacitor with battery controller, and put it back battery slot (It's small and fits)
And you can boot on cable power without battery!

In case you still look for a solution, I would connect a functioning Li-Ion battery, either 18650 or from another phone with at least 2000mAh capacity and hook a single cell Li-Ion charger with at least 1A rating.
Things to consider:
- the charger is likely to be noisy and needs a battery to smooth out the wave. It may or may not be an issue. Having a battery connected will dampen it down.
- connecting a smaller battery and powering the tablet via USB may dump too much current into the battery
- the tablet may draw up to 4A on boot, probably 800mA min, so your charger will need a full battery as a backup
- don't use a charger for a different battery chemistry. There is a chance of damage or even fire.
- some devices use I2C interface to talk to the BMS, but this is unlikely in your case
- make sure the temp battery you are using has a BMS

NST battery voltage shutdown treshold hackable?

Hi,
i use a Nook Simple Touch as typewriter with an usb-keyboard,
which works great thanks to the usb host mode app, or, automated:
an old version of tasker with a plugin to deactivate charging and activate hostmode ( and fastmode...) via shell command after booting.
The problem is, this mode drains the battery really fast,
and charging while using the keyboard, so nececessarily with OTG cable attached, is a bit of a pain in the neck,
because there is only 1 possible sequence of actions how you can enable charging with more than around 100 mA (which would be way too low in this case) while the keyboard is active,
which requires a 16k resistor between GND and ID pin, rebooting, temporarily disconnecting some wires via switch, tapping around etc etc,
(and also does not work well when the nook is completely off ),
so i decided to leave the usb port exclusively for the keyboard,
an remove the internal battery an replace it with a external big 7000mAh or so 1S li-ion pack,
which is charged externally with a lipo module
(while charging, the nook is powered by an ac adapter, power source switching is realised with a relay and a really big capactior to avoid any more complicated possibly failing electronics)
which works great and is very easy to handle,
BUT i really dont like li-ion batterys of any kind because of the fire hazard,
nimh eneloop cant be used because charging in parallel is not a good idea,
so i would like to use lifepo4 chemistry instead,
which has a working woltage between around 3 and 3,6 volts,
but the nook powers down at around 3,65 volts.
A boost/buck converter isnt possible because as the battery drains, the voltage must sink slowly for the nook to make a normal shutdown
and not crash, damage the file system etc, (and also a converter drains quite much battery even if the nook is completely off.)
Question: it would be VERY kind if anyone who has a clue about this could share his opionion on that:
is it possible (if the hardware itself can handle it) to lower the android/nook shutdown voltage to about 3 volts with some rom/software modifications ?

threshold not treshold

Wow, this all seems a bit complicated.
I had never heard of this 16K resistor stuff.
As far as I could tell, the ID pin is only sensed high or low..
Unless I'm mistaken the OMAP3621 ULPI registers only indicate high/low.
The TPS65921B (which is the actual PHY) list 90K as the typical break point.
Of course, there could be a circuit completely external to the ULPI/PHY.
Where did you find out about 16K?
Changing the voltage of everything seems the difficult way to go.
You'd have to modify uboot as well as the charger daemon.
A note: The USB charge pump is pretty inefficient, 55%.
If you were to load the USB to the maximum speced 100mA with a 3V battery, it would be drawing 303mA from the battery!
5V × 100mA / 3v / 55% = 303mA

Oh, you got me confused with your two posts.
When you were talking about ID and 16K did you mean the ID on the battery pack or the ID on the USB OTG?

Renate NST said:
Where did you find out about 16K?
Click to expand...
Click to collapse
wired a 50k pot between gnd and id pin,
in the usb mode app tapped "host" and watched if the led goes an stays on,
if not, lowered the resistance, tried again etc,
as soon it stayed on (at 16k at my device ) used this value as permanent fixed resistor.
with that otg mode keyboard use is possible,
but also at the same time the nook doesnt really believe its in otg mode so charging with 500mA is possible,
if done in this order:
- feed 5v to the + - of the usb cable
- reboot (not always required)
- remove an reinsert usb plug
- hit "host" 2 times, keyboard works and charging with around 500mA works (measured it)
but charging doesnt work when nst ist powered off,
and automount of the keyboard at startup via shell is not possible,
and cable acrobatic is required,
and as you say, usb charging is inefficient.
the other solution with an external battery (at the nst batt terminals) with external charging logic with a relay is a much easyer way,
but depends on a li-ion cell because of the 3,7-4,2 voltages the nook can use,
a lifepo4 ( or 2s li titanate + diode) would be safer and has more cycles but would require the nook
to work with 3 to 3,7 volts, which seems too complicated, changing demons etc whatever that is...
after some research it seems its not really an issue, the newer sanyo/panasonic, samsung, sony, lg powertool/ebike cells seem to be quite safe, as far as youtube shortcircuit etc tests demonstrate.
thanks for the orientational infos

Renate NST said:
Oh, you got me confused with your two posts.
When you were talking about ID and 16K did you mean the ID on the battery pack or the ID on the USB OTG?
Click to expand...
Click to collapse
sorry, i should have used one thread, i suggest ignoring the other one,
where the only request was if the nook battery terminals can survive up to 5v,
here was the request if the nook can be modified to accept at the battery terminals a voltage down to 3v and stay on.
so 3v too complicated, 5v too dangerous,
so i stick with the relay and the li-ion cell, no problem, i was just curious if an improvement would be easily possible.
the battery id resistors have nothing to to with all that, 10k and 30k work fine,
i meant the 5 pin micro usb otg connector, not shorted zero ohms as usual, but 16k.
(but thats obsolete now)

another observation: in some thread you mention you charge the nook while using an usb keyboard,
i tested it and with a normal otg cable, and the usb mode app set to 500 mA oder 1,5 A,
and a 50% charged normal internal battery,
the device draws around 250mA, and the battery gets charged very slowly, or not at all, depending on cpu usage etc.
and if the battery reaches 100% , it continues to draw around 250 mA, which is strange,
because when using a normal, non-otg usb cable,
the device draw only around 100mA when the battery had reached 100%,
so the difference must be used for heating purposes somewhere or overcharge the battery,
which might be a reason for swelling lipos.

Has anyone tried connecting 5 Volts directly to the internal battery terminals ?

Does it damage the Board or not?
I accidentally did connect 5v for a second or so,
it did power on, i disconnected immediately, and after that it didnt power on for several hours,
but not sure if it was because of the interruption during boot, or overvoltage.
Can somebody confirm?
(i cant use a diode for voltage reduction, its a bit complicated, i use a load sharing capable solar charger board etc)

its a nook simple touch

Yow, don't do that!
Ok, it should be able to take it, but still.
I've often fed 4V to devices which had their battery blow up.
In worst cases I've used a diode for drop, but the voltage can be pretty variable over load.
The uboot on most things will not continue if there is zero voltage on the battery.
Also, the peak current of a device can go up to 600 mA or more at times.
That kind of current often can't come in through the USB connector.
Finally, battery packs have ID connections and thermistor.
Entirely disconnecting a battery pack will often prevent booting even when voltage is present.
If you have a dead battery pack always keep the the connector, cable and tiny PCB inside.
Attach a power supply to where the naked cells used to connect to the PCB.
For wiring of the battery pack see: https://forum.xda-developers.com/showpost.php?p=42552349&postcount=5

thanks, 2 weeks ago i prepared to measure possible resistors but did a google search before, found your description...
i use the protection board with a 18650 3000mAh lithium manganese (to prevent blow (up)) etc cell and charge it externally,
which requires switching between charging the batt + powering the nook over the batt terminals,
and using the batt for powering the nook , all that while the usb keyboard is connected and in use,
this is done via relay and a really big capacitor, which works great but is a bit ghettostyle.
i tried to use another charger board with load sharing circuitry instead,
but the only easy available module requires 5v minimum input, passes this 5v to load if the ac adapter is plugged in,
if not, it passes the battery voltage to load,
so a diode(+ parallel resistor to maintain voltage drop) or LDO doesnt work because it would at least steal around 0,5 v,
which is to much reduction for the battery voltage, because the nst powers off at ~ 3,7v,
easiest would be to just let the 5v to the nook but seems no good idea.
anyways, it works with the relay