## Minor Android Update Tonight

My Samsung Galaxy S6 smart-phone runs Android 7.0, and received a minor system update tonight, which only required that 18MB of software be downloaded. The update completed quickly, but it will require some more, extensive use, before I can know whether the promised stability and security improvements are apparent.

I was never really dissatisfied with the phone’s stability.

Dirk

## The GSam Battery Monitoring App

On my Android smart-phone, I have the third-party “GSam” battery monitoring app installed.

This app can be a useful tool, to determine which other apps are causing the greatest battery drain. It gives very detailed information about the battery and its charging behavior.

Further, this app will state the battery voltage – in addition to the percentage charged – any time it is clicked on. This is where I obtained the numbers I used in this earlier posting.

At lower current-levels of battery-drain (-13mA), this same app showed the battery as 96% charged, but with a voltage of 4.24V . The app continues to run in the background, when the phone is asleep, and when the phone may be drawing much less current than it does with the display on. Then, after we wake up the phone, this app initially displays with its remembered values, until a few seconds later, the app-data updates.

(Edit 12/14/2016 : In the case of a soldered-in battery, it would make perfect sense if the O/S of the device computed the State Of Charge as a linear function with two fixed voltage end-points, as well as to compensate for the amount of current drawn, as if the battery simply had an assumed series-resistance. This is because a soldered-in battery is not assumed to be changed. However, multi-pronged battery-packs also exist, which possess internal chips. Those could be exchanged easily by the user.)

(Edit 12/12/2016 : Actually, this app does not tell the phone, what the State Of Charge of the battery is – the Percentage Charged.

And so there will be a scattering of relationships, between voltages as measured by the device, and percentages. However, one concept which intrigues me, is that if each battery-pack has 4 prongs, there is no way for me to rule out, that 1 prong could be for discharging, while 1 prong could be for charging.

If that were the case, then the charging circuit would detect that the battery suddenly seems to stop drawing current from its charging terminal, and could then immediately measure the voltage on the discharging terminal.)

The advantage this would offer, instead of setting up an arbitrary communications-protocol between a battery and its device, is a simpler internal chip as well.

But If somebody did that, it would still assume a fixed low-endpoint voltage, corresponding to a Sate Of Charge of 0%. This might as well be the voltage, at which Li-Ion Batteries generally start to produce Li2O , which I think is at 2.5V .

(Edit 12/13/2016 : Actually, the battery of the Samsung Galaxy S6 Phone is soldered in. Therefore, it does not need to be an info-battery, and only has 2 terminals.)

## A Note on Sample-Rate Conversion Filters

One type of (low-pass) filter which I had learned about some time ago, is a Sinc Filter. And by now, I have forgiven the audio industry, for placing the cutoff frequencies of various sinc filters, directly equal to a relevant Nyquist Frequency. Apparently, it does not bother them that a sinc filter will pass the cutoff frequency itself, at an amplitude of 1/2, and that therefore a sampled audio stream can result, with signal energy directly at its Nyquist Frequency.

There are more details about sinc filters to know, that are relevant to the Digital Audio Workstation named ‘QTractor‘, as well as to other DAWs. Apparently, if we want to resample an audio stream from 44.1 kHz to 48 kHz, in theory this corresponds to a “Rational” filter of 147:160, which means that if our Low-Pass Filter is supposed to be a sinc filter, it would need to have 160 * (n) coefficients in order to work ideally.

But, since no audio experts are usually serious about devising such a filter, what they will try next in such a case, is just to oversample the original stream by some reasonable factor, such as by a factor of 4 or 8, then to apply the sinc filter to this sample-rate, and after that to achieve a down-sampling, by just picking samples out, the sample-numbers of which have been rounded down. This is also referred to as an “Arbitrary Sample-Rate Conversion”.

Because 1 oversampled interval then corresponds to only 1/4 or 1/8 the real sampling interval of the source, the artifacts can be reduced in this way. Yet, this use of a sinc filter is known to produce some loss of accuracy, due to the oversampling, which sets a limit in quality.

Now, I have read that a type of filter also exists, which is called a “Farrow Filter”. But personally, I know nothing about Farrow Filters.

As an alternative to cherry-picking samples in rounded-down positions, it is possible to perform a polynomial smoothing of the oversampled stream (after applying a sinc filter if set to the highest quality), and then to ‘pick’ points along the (now continuous) polynomial that correspond to the output sampling rate. This can be simplified into a system of linear equations, where the exponents of the input-stream positions conversely become the constants, multipliers of which reflect the input stream. At some computational penalty, it should be possible to reduce output artifacts greatly.

## I am currently charging my phone wirelessly.

My phone is a “Samsung Galaxy S6″. It is not an ‘S6 Edge‘, nor an ‘S6 Edge+’. As the ‘S6′ goes, when it was first released onto the market, this phone was considered to be advanced, because it did not require a special cover for wireless charging, and because the built-in charging capability included compatibility with both the ‘Qi’ and the ‘PMA’ systems, which were maintained by independent companies.

Yet, by default I had been charging this phone with a USB cable and a special USB wall-power adapter, that lets the phone know via the data wires that it can draw 2A of charging current, instead of 500mA. Doing so always put wear and tear on the USB jack of the phone.

Starting a few days ago, I had bought myself a Qi wireless charging pad by the brand-name “JETech”, and I find that this charging pad does the job well. I was surprised to learn, that these charging pads no longer come with 110VAC cords to plug in, but that we connect the pad to its power source, via the 5VDC, 2A, USB power adapter.

Charging the phone from 50% all the way back up to 100% via Qi-wireless takes about 1 hour and 20 minutes time, which I think is impressive.

But there is a more recent development in this realm, that I should also mention. Starting with the ‘Note 5′ and the ‘Samsung Galaxy S6 Edge+’, and including the ‘S7′, Samsung has decided to produce its own type of wireless charging system, which is supposed to be even faster. In fact, when I first went to the store to request a charging pad for my S6, the tech person in charge automatically sold me a ‘Samsung Fast Charging Pad’, knowing the fast charging feature would only work with the Edge+, but nevertheless assuming that slower charging would still work with my S6.

As it turns out, the Samsung Fast Charger that I received did not work with my S6, even at standard charging speeds. This could be due to an incompatibility, or due to one defective unit sold to me. I rather suspect the former. The symptom was, that charging would seem to begin, but that after charging for about 1 second, charging would pause, and that 1 second after that, charging would start again – endlessly. And this would also happen eventually, after I had removed the phone from its case, which in my case is an “Otter Box”.

So I had to return the Samsung-brand Charger to the store, where I received a refund. And that was when I decided to buy the ‘JETech’.

The JETech actually does a better job on my S6 than the brand charger did, especially since in my case, the brand charger only produced an endless series of notifications, and accomplished no charging effect at all. And I can leave my phone in its Otter Box case, while charging successfully on the JETech pad.

If it becomes possible for my use of the JETech charging pad to replace my former use of the Micro-USB-port on the phone completely, doing so may also increase the overall usage period of the phone, since if it was ever to become impossible to charge, it would also become impossible to use…

Dirk

(Edit 03/23/2016 : ) I had observed that modern devices with USB charging have some mechanism by which to increase the charging speed from ‘Cable Charging’ to ‘Fast Charging’, which the notification will indicate. I also know that usually, the power source will define the voltage, while the load will decide to draw some amount of current. It all becomes difficult to manage, at low voltages and high current levels. But I had not known the exact details until today.

At least with Samsung, the way this works is as follows:

An “Adaptive Charger” is capable of delivering either 5VDC or 9VDC. At 5VDC, it can handle loads of up to 2A. At 9VDC, it can handle loads of up to 1.67A. The device to be fast-charged actually sends a signal to the charger, which triggers it to deliver 9VDC on the USB cable, instead of the usual 5VDC. At 9VDC, Fast Charging mode can commence.

One problem with fast-charging at 5V would have been, how impractically close this voltage is to that of the battery in the mobile device. A fully-charged Li-Ion battery has approximately 4.5V, which is only 1/2 Volt less than the standard USB voltage was.

Wires, connectors and control circuits all add series resistance to a circuit, and even if the series resistance was only 1/2Ω (Ohm), then at a theoretical current of 2A, the circuit would lose 1 Volt right there. This would put the voltage arriving at the battery at 4V, which is already lower than that of the battery nearly charged. And so it would have been an improbable – and destructive – feat to get the device actually to draw 2A when connected to the USB port of a computer.

The version of what happens which I now entertain, is that the USB port of a computer may have a ‘current-limiting transistor’, which limits the output current to 500mA actively, even if doing so only means inserting a resistance of 1Ω (Ohm), and thus inserting a voltage drop of 1/2V. It may be the case that when connected to a charging adapter capable of supporting 2A at 5V, the actual mobile device still achieved much less charging current than that.

Dirk