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Author Topic: DIY Cintiq Companion [Design Phase]  (Read 5200 times)
Ertew
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« Reply #30 on: May 27, 2016, 12:26:51 AM »

To discharge good lithium battery You need to know overall voltage, divide by number fo cells and cut-off load (computer) from battery when voltage drop do much. It's nice to calculate remaining capacity of battery and measure actual voltage, so OS can display battery status and remaining working time.
When You have bad quality battery, each cell may have different capacity. In that case You need to know all voltages and do calculations for worst cell.

To charge You to do same thing plus balance the packet. Charging should be constant current as long as all cells are below 4.1 or 4.2V for Li-po/Li-ion (there are LiFe / LiFePO4 with different voltages). When voltage rise to that level, You need do decrease current step-by-step as long as You go to some minimal current (usually 1/10 of charging current or C/10). What when one cell have more than 4.2V and other less than 4.0V? That's situation when balancer put small load on all cells with voltage above specified level. In that situation charging current should be decreased and charding should be slowly finished - cells with lower capacity have higher voltage so takes no current (charging current flow through balancer, not through cell) while cells with higher capacity have lover voltage and were charged up to full voltage.

Too high or to low voltages, to high current or temperature and battery may blow up or catch fire. Too complex for me to make it safety. You should have the same opinion.


Next part is power management - how to not exceed total input current while CPU running and battery charging, how to fast switch between supply and battery, avoid charging while working from battery (decrease cells life a lot), etc...
Seems harder to implement, but doing it wrong cannot destroy battery.



I'm planning to build my own tablet, but with 20-30W total power consumption (most power goes for rPi and backlight) of the shelf solutions should be more than enough.
I have batteries for ST5111/ST5112 (huge capacity and still good after years) and charger for it. Everything should fit into case. If not, i need bigger case.
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Rubatonk
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« Reply #31 on: May 27, 2016, 01:06:00 AM »

the battery im using is a 4 cell from the dell m14x type PT6V8 made by samsung. each cell voltage at max is 3.7v and the min is 3.3v, nice balance between capacity and reliability and its super slim. Computers are 12v so that is 7v that can be used for the battery charging. i chose the controller chip i did because i can program the batterys min voltage and max voltage so i dont over or under charge the battery. my only set back with it is that i dont know how to set up the interface to program the chip. texas instruments has a nice program for it they just dont explain how to connect it to the pc. i've never gone this extensive with circuit boards and such, the most i've done is replace a capacitor or resistor, and once a bios on a laptop so this is new ground to me but its a nice place to learn
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Ertew
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« Reply #32 on: May 27, 2016, 11:14:28 PM »

If You use typical laptop battery, many problems will disappear:
- Laptop batteries always have controller that cut-off battery if anything is wrong with cells. That's very safety solution.
- Controller always can talk with MoBo via SMB. In Your design, You can read full and remaining capacity, voltage, current, temperature, remaining time, etc... That's very easy to implement.
- Laptop batteries usually have 'good' cells. (By that I mean that whole packet is balanced. Not the overall quality.) Because of that, cell balancing wasn't a huge problem.

Things You still need to solve:
- Control voltage/current and terminating charging. Battery will cut-off at 4.3V and 3.0V/cell - safety but give short lifetime.
- Turn on/off battery. Yes, that's real problem. Some batteries gives 3v3 output trough serial resistor. Shorting this to GND or another pin will enable normal output. On the other hand, some batteries provide power output without tricks but You need talk via SMB to enable charging.
In my opinion, simplest way for You is to buy a 'laptop battery charger', something like shown on links below. If You have choice, chose official model or something dedicated for Your battery. Chinese universal models wasn't the best option.
https://www.google.pl/search?site=&tbm=isch&q=laptop+battery+charger&gws_rd=cr
http://www.diytrade.com/china/pd/6276264/laptop_battery_charger.html
http://www.aliexpress.com/item/Universal-External-Laptop-notebook-Battery-charger-with-2-different-universal-connecting-wires-connectors-NEW-ARRIVAL/528778258.html
http://www.aliexpress.com/store/product/Professional-Universal-External-notebook-Laptop-Battery-charger-with-whole-connectors-for-almost-all-the-laptop-batteries/203437_558891609.html
http://www.repower.cn/en/Products/product_44.html
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Rubatonk
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« Reply #33 on: May 28, 2016, 08:37:25 PM »

Ok so after a couple days this the circuit that should work, the usb interface will terminate to 4 pins in case it is not just a simple usb connection like im hoping, still working on the pcb layout
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Ertew
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« Reply #34 on: May 28, 2016, 10:04:33 PM »

Schematic looks good, but I not have enough knowledge to approve it.

One thing that doesn't fit is the PAD3..PAD10 connector. Do You wand to connect battery there?
IMO battery have one or two negative terminals and same positive. Connecting all 8 terminals do supply pins wasn't good solution. Look for "laptop battery pinout" and You will see that laptop batteries have I2C/SMB on pins = You can talk with battery same as You can talk with the charger. Applying to this pins more than 5V was insane.
https://www.google.pl/search?q=laptop+battery+pinout&hl=pl&source=lnms&tbm=isch&gws_rd=cr
http://nathandumont.com/files/images/battery_pinout.jpg
http://www.gearhack.com/Forums/Computer/Notebook/Rebuilding_the_Sony_VAIO_PCGA-BP51_Li-Ion_notebook_battery_pack.files.hidden/PCGA-BP51%20interface%20pinout.JPG

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As I see in datasheet, bq24725 give automatic supply switching, charging current regulation and charging cut-off at specified voltage.
Laptop battery should have cell balancing and emergency cut-off.
You still need some logic that can turn off laptop when battery voltage drop below certain voltage - it can be done at SMB controller that was connected to bq24725 and battery via I2C interface.
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Rubatonk
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« Reply #35 on: May 28, 2016, 10:27:55 PM »

I figured i need to use 8 pads for the battery as  the battery has 4 positive wire's 4 negative wire's and a few other wire's that i dont what know are for.
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XDjackieXD
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« Reply #36 on: May 29, 2016, 10:12:07 AM »

I don't want to ruin your dreams of USB but the bq24725 only has I2C (the bus system used by SMBUS. SCL being serial clock and SDA being serial data).
Your computer should have this bus somewhere on the motherboard and connecting this controller to it should make it visible to the os via ACPI (if you are lucky. if not then there is some configuration of the chipset required).
Also I have to confirm Ertew's statement: Laptop batteries don't just have + and - connectors. at least two of the pins are data (probably I2C too. charging cycles and capacity are stored on an eeprom inside the battery) and most of them require a pin to be pulled to ground to activate the battery.
For example the battery charging and controlling is described on page 43 & 44 of this document: http://ftp://helpedia.com/pub/temp/uploads/ala_borbe/ACER/Compal%20LA-8241P%20QCL00-QCL20.pdf
(The diodes and resistors directly at the connector are for ESD protection)
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Rubatonk
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« Reply #37 on: May 29, 2016, 08:12:38 PM »

many thanks for the information XDjackieXD and Ertew, im willing to accept any information you have to offer as im new to making my own boards
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Rubatonk
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« Reply #38 on: May 29, 2016, 08:18:50 PM »

Also the motherboard has a com port on it does that help with the serial interface in anyway?
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Ertew
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« Reply #39 on: May 29, 2016, 08:31:46 PM »

In most case, COM port not help but made things worse.

Every Wacom tablet need drivers.
ADB tablets are obsolete because apple drop ADB connectors.
Serial tablets are obsolete because Wacom include drivers for them up to Win XP. Win 7 and above cannot handle serial tablet in any normal way. You can install old drivers for Win 7 in compatibility mode but that trick may not work in some cases.
That's why WaxBee project exist.

Of course, if You have Linux, problem never exist and You can use serial port.
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XDjackieXD
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« Reply #40 on: May 29, 2016, 08:39:11 PM »

Also the motherboard has a com port on it does that help with the serial interface in anyway?
Not really for the battery controller or the tablet as serial wacom drivers for Windows >7 are virtually nonexistent.
Regarding the battery controller & battery you have the SMBUS lanes (SDA & SCL) somewhere on the motherboard (the 2 pins should also be on each PCIe connector iirc).
It is a bus system so you can connect many different peripherals to the same 2 lines
(each IC has it's own address. Therefore connecting different ICs is no problem but same ICs could be problematic as they have the same address).
In theory this should autodetect your battery controller and show it to the OS via ACPI as laptop battery and it's corresponding controller.
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Rubatonk
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« Reply #41 on: May 30, 2016, 02:14:38 AM »

I decided to take a break from the power supply board as i've spent 3 days on it so i refined the model a bit more so here are some renderings. Still have not yet decided on the stylus silo or the stand/visa mount yet. For the ethernet jacks im going to do what i've seen on many samsungs and make a little fold out piece so when its not it use it will look better




« Last Edit: May 30, 2016, 02:17:29 AM by Rubatonk » Logged
Rubatonk
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« Reply #42 on: June 03, 2016, 05:46:50 PM »

Ok so this is the solution i came up with for the stand, its has a maximum angle of 150 degrees which should be a comfortable drawing position and of course it can be set to any position within 0-150 degrees
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thatcomicsguy
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« Reply #43 on: June 07, 2016, 12:34:35 PM »

This looks like a cool design.  I'll be watching with curiosity to see how it goes.

Good luck!
« Last Edit: June 07, 2016, 12:41:26 PM by thatcomicsguy » Logged
Rubatonk
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« Reply #44 on: June 07, 2016, 04:43:20 PM »

Thanks, right now im just playing the waiting game for parts to arrive
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