Android-powered Tablet PC for reading books

A few days ago, I bought MoveO TPC-1VX Tablet PC (in Russian) with Android 4.0.3 on board. It features 7" multi-touch 800x480 screen, 4 Gb of built-in flash memory, 512 Mb RAM, and other characteristics are on the line of other devices in this price sector. I wanted low-cost handheld PC mainly to be able to read books (PDF, HTML, and other standard formats). It is much more convinient to do this on 7" than on 3.6" screen. It even fits into pocket of my sleeveless jacket. By far, I have not observed any bugs or software freezings. Maybe one day I will write a program for Android platform. At last, Android today is the most popular OS for mobile devices.

P.S.: well, I already have bicycle and Tablet PC. The only thing left to buy is reflex camera, and I will completely fit controversial folklore image of a young programmer :)))

Radio-controlled all-wheel drive Robot based partly on Arduino modules

Today I have attended Chaos Construction 2012 (in Russian) - computers and computer graphics, 8-bit music and demo scene annual festival. For me, one of the most interesting things there was presentation of all-wheel drive radio-controlled robot made partly based on modules from Arduino open-source electronics prototyping platform.

Robo-hobby blog (in Russian) is the official current webpage of these guys (those who are working on a robot, not those who develop Arduino). If you will ever want to learn anything about relatively easy-to-reproduce hand-made radio-controlled robots based on open-source hardware & software components, I would advice to check this blog. Authors share their experience about working on such a project. This is really interesting, even for me, professional electronics developer. I've already added RSS feed of their blog into my feed reader.

Reanimating NiMh Battery Pack in home cordless phone

At home, we have cordless "TELECOM" phone. This summer, after two weeks of idle time during our vacations, it refused to continue working. It also refused to charge its pack of 3 NiMH batteries (T160 600 mAh 3.6V D4 marking). I.e., green LED which should indicate chraging process and presence of phone tube on the base module did not turn on when I tried to start charge the cordless receiver by putting it to its place (its dedicated socket). I tried to apply the same method I used for my LiIon smartphone battery (see my previous post on it): firstly to charge battery directly via lab DC power supply. The difference is that this pack of 3 NiMH batteries does not have internal built-in charge controller, so there is no need to disclose internal connector pins. I set up output voltage to about 4 Volts, and max. current to about 50 mA. After approximately 2 hours, power supply switched from constant current into constant voltage regulating mode, and I disconnected the battery. After placing this slightly recharged battery back into cordless phone tube, and putting this tube back on base station, green LED which indicates charging process, turned on, and device continued to work in normal mode. Apparently, charge controller built into this phone tube needed for its operation higher voltage than discharged battery was able to deliver. So be aware of this method, and do not throw out your battery prematurely.

UPD: the same method works with NiMh AAA accumulators, I've just checked this today. 900 mAh acc. battery discharged to ~0.7 volts has been charging with ~90mA current for a few hours, after that I was able to complete the process with standard charger.

P.S.: Caution! In absense of temperature monitoring circuit, do not charge the battery with currents more that 0.1*C, for example, in my case I had battery with 600 mAh Capacity (designated by capital "C" letter), so max. safe charging current was 60 mA. Also, do not try to repeat this without proper setting of output voltage limit in your power supply. Put the battery into protective box for a period of charging to prevent damage from its possible explosion. Make sure that you are ready to quickly disconnect the power supply and to extinguish a fire in case if it will arise.

How to reanimate Li-Ion or Li-Pol battery from your smartphone

Today I want to share my experience in repairing the Li-Pol smart battery in my HP iPAQ 1930. See my previous post on it.. My battery was marked with HP H1910 string on its paper box. The problem with it is if you'll leave device without even a single charge cycle for several weeks, it will discharge to a level from which it is impossible to initiate further recharging. If nominal voltage is 3.7 Volts, and you have allowed to discharge to about 3 V, this is the situation considered. A small piece of electronics, consisting of charge controller IC (integrated circuit), and a couple of power field (MOSFET) transistor keys, is placed between actual Li-Ion (or Li-Pol) battery and the outer contacts. Charge controller IC monitors voltage levels at the battery itself and outer contacts, opens necessary power key transistors, and communicate with host device via SMBus or other protocol to allow it to know state of the battery. Problem with discharging of a battery below certain level is that this controller IC stops working, so it is impossible to recharge the battery, since power key transistor have become permanently closed. But in many cases it is still possible to reanimate the smart battery.

To do this, cut off small pieces of plastic from both sides of the battery, to open access to the inner contacts of Li-Ion (Li-Pol) battery. You should see and have access to two metal stripes after this operation. Get laboratory DC power supply unit, with both constant current and constant voltage, modes of operating. I use SHENZHEN MASTECH HY3005D-3. Constant current mode is indicated by "C.C." red round LED at the front panel, while constant voltage -- by the nearby LED named "C.V.". My battery has capacity of 950mAh. The usual current for charging Li-Ion batteries is calculated as capacity x 0.2 (in the appropriate units, in my case, it would be 950 x 0.2 = 190 mA). Since we want to bypass control electronics, and will not monitor temperature of the battery, it would be safer to decrease this value, I think, two times will be enough, so I assumed charge current of 100 mA. I shortened outputs of one channel of SHENZHEN MASTECH HY3005D-3 power supply unit, and set short-circuit output current to this level. (Be aware also that maximum allowable current that USB port should be capable of providing by its spec, is 500mA. So if your device is charged through USB, do not exceed this value under any conditions. Even safer would be to use half of that value, that is, about 250 mA, as an upper threshold for charging current.) Then I set output voltage to nominal voltage of the battery, 3.7Volts in my case. After this, I connected output of power supply to inner batteries contacts. Initial current will be 100 mA, equal to short-circuit, and "Constant Current" LED should be active. During a few hours, the battery will be charging, after which voltage should rise to its nominal value (3.7 Volts in my case), current drops to near zero, and power supply switch to "Constant Voltage" mode. That's it. Now you can power off power supply, disconnected wires from battery, place it into your handheld device, and continue using it, without having to buy a new battery.

WARNING 1: Do not try to repeat the process without power supply with both "Constant Current" and "Constant Voltage" output mode, and without proper and carefully checked set-up values.

WARNING 2: Li-Ion batteries might fire and explode. It is safer to put the battery into the metal or other solid case during the process to avoid possible harmful accidents.

Digital Photo Frame Texet TF-618

Last week, I had have to choose digital photo frame as a New Year gift to my mother. I stopped at Texet TF-618 due to its placement of control buttons at the front panel instead of at the backside. All other devices that I saw, have built-in control buttons made as usual mini-knobs, at the back side of them. TF-618 have just opposite design solution: a series of sensor LED-highlighted buttons at the front, just below its screen. This, I suspect, does not significantly raise its cost, but make usability and feel of control much better. I do know that there is small remote infrared control unit supplied with almost each digital photo frame device, including TF-618, but I prefer to have ability to deal with device without it in case it will be lost or accidentally hidden somewhere.

Using of Pocket PC for Reading Books

I have an old Pocket PC iPAQ h1930 with Windows CE 4.20 on board. I'm not interested in beautiful flash games or watching video on it, so it serves me well for the purpose of reading books. It has about 3.6'' inches screen diagonal, so it can be put into any pocket, that is very handy. It does not have built-in GSM transceiver, so I have to use a separate cell phone in addition. This scheme has three main drawbacks:
1. When you have two devices instead of one, it is easier to forget one of them or to forget to charge one of them.
2. When you have a scanned book in PDF format, Adobe Acrobat, even in "Reflow mode", cannot reformat the strings to shorten them and to fit them into the available screen space. So if with minimum acceptable scaling value the text strings do not fit into the screen height, you have to constantly drag the document view back and forth in order to be able to see the whole sentences. This is rather annoying, although with some practice you become to pay much less attention to it.
3. Sometimes the device for unknown reason goes into totally unresponsive state, and I have to do a hard reset via special technical button and a pen. It happens about once a week or in a few days.

Although despite the above cases, the device saves me a lot of time by allowing me to educate myself during trips in public transport, and I understand, that buying any new modern gadget of similar form factor will not improve my productivity in this area. Electronic books have larger screens, but they are less handy to put into your pocket.

What I like in the device, is that there are many applications already written for Windows Mobile, so I have no problems with viewing of virtually any needed file format. Yes, I know that this OS is in fact abandoned by MS, but this does not matter, since all practically required applications are already there.