Browsing Android Files using Bluetooth

One of the casual uses of Bluetooth under Android, is just to pair devices with our Android (host) device, so that specific apps can use the paired (slave) device. This includes BT-headphones, and many other devices.

But then a slightly more advanced use for BT under Android could be, that we actually send files to a paired Android device. It’s casually possible to take two Android tablets, or a tablet and a phone, and to pair those with each other. After that, the way to ‘push’ a file to the paired device, from the originating device, is to open whichever app displays files – such as for example, the Gallery app, if users still have that installed, or a suitable file-manager app – and to tap on ‘Share’, and then select ‘Bluetooth’ as what to share the file to. Doing this should open a list of paired devices, one of which should be suitable to receive a pushed file in this way.

But then, some people would like to take Bluetooth file-sharing up another level. We can pair our Android device – such as our phone – with a Bluetooth-equipped, Linux computer, which may be a bit tricky in itself, because the GUI we usually use for that assumes some legacy form of pairing. But eventually, we can set up a pairing as described. What I need to do is select the option in my Linux-BT-pairing GUI, which requires me to enter the pass-code into the Linux-GUI, which my Android device next displays…

And then, a question which many users find asking themselves is, ‘Why can’t I obtain FTP-like browsing capability, from my Linux-computer, over the files on the phone? Am I not giving the correct commands, from my Linux-computer?’

Chances are high, that any user who wishes to do this, is already giving the correct commands from his or her Linux-computer…

(Updated 06/03/2018, 20h45 … )

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Distinguishing between Different Battery-Types

One of the things I recently did, was to pair my Linux-laptop, which I name ‘Klystron’, with an external Bluetooth-Mouse, because even though this advanced, HP laptop has as its hardware, an advanced Synaptics touchpad, that emulates a mouse quite well, we can grow tired of always using the built-in touchpad. I documented here, what I needed to do, to accomplish this pairing.

Well one of the features which the KDE Desktop Manager gives us under Linux, is to indicate the battery-charge-levels, not only of the laptop’s built-in battery, but also those of attached BT-mice, or of anything else which is connected, that has a battery, and the hardware of which is able to report as telemetry, the battery-level.

What was surprising me about this arrangement, was that the indicated battery-level of the mouse seemed to track accurately over the days, that the mouse was connected. This surprised me, because as I was remembering events, I had placed Nickel-Metal-Hydride batteries into the mouse some time ago, and most devices which are physically designed to accept batteries in the AA-format, or in the AAA-battery-format, would be calibrated for Alkaline, Zinc-Manganese-Oxide batteries. When such accessories try to gauge the battery-level, if they have the chip to do so, the voltage-curve of a Ni-MH battery tends to remain lower than that of an Alkaline. A fully-charged Ni-MH only generates about 1.2V per cell, while an Alkaline generates 1.5V. And so when a Ni-MH battery is inserted, this chip will usually indicate a partially-discharged battery, even immediately after it has been charged, and then, when this battery-type finally goes dead, its voltage will collapse almost instantly.

Before the indicated charge-level dropped below ‘70%’, I decided to take the AA-format batteries out, and to put them into a charger I have, that’s designed for Ni-MH batteries, and what I found was, that the LEDs in the charger refused to light up, for the inserted batteries. They did not indicate partially-charged or anything, they just stayed ‘off’.

And so next, my thinking was, ‘Darned! I now have either batteries which have failed on me, or worse – a charger which has failed on me 100%…’

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My ongoing experiences with my Linux laptop and this time, Bluetooth.

One of the observations I had written earlier, about the Linux laptop I name ‘Klystron’, illustrated in depth that it has issues with its Realtek chip-set, that provides it with both WiFi and Bluetooth connectivity, presumably providing both through the same physical antennae.

> BTW, have Linux developers ever discovered, that this chip is meant to have two antennae, which the laptop was built with, and that the drivers are supposed to switch back and forth, to whichever antenna was giving the best signal at any moment? I.e., that with the lid open, one antenna should be used, while with the lid closed, the second antenna should be used? I just thought I’d mention it as a segway… <

The Bluetooth functionality of this chip-set, on my Linux configuration, does not seem to work at all. And so something which I have done, which some people might find odd, is to buy a Bluetooth-dongle, to put that in a USB-port on the side, and then to pair my external mouse.

Actually, this has only worked on a second attempt, with a second BT dongle. I had given up on the first BT dongle, thinking that that dongle must somehow have been incompatible with the Bluetooth Stack in some way, failing consistently on both my Debian / Jessie / 8 systems. And I had erroneously come to that conclusion, even after the same, first dongle worked fine, on a Debian / Squeeze / 7 laptop.

The actual user-space software works fine, even telling me that the newer, better, $5 dongle detects the Realtek chip with its antenna only 20cm away (where it’s inside the attached laptop), and with my neighbor’s sound-bar detected upstairs from my flat… For another day.

I know that my ( “Logitech M557″ ) BT mouse works fine, because I can pair it easily with my tablet(s).

There is a bit of a trick, that will finally enable the Debian / Jessie laptop to pair with the same mouse. I need to use the GUI normally, to tell it to pair, while the mouse is in pairing mode, at which point the GUI shows activity for a few seconds, and the data-exchange-bars just seem to cease, and the mouse next stays in pairing mode, with its own blue LED still flashing rapidly, waiting to pair.

What seems to go wrong, is that after Linux has established a pairing, Linux fails to send a signal to the mouse, that it should switch from pairing-mode, to usage-mode, so that its LED extinguishes.

The way I found this out, was to wait after the data-exchange-bars in the Linux GUI vanish, where that mouse still has its Paired and Trusted icons, until the mouse ‘decides on its own’ to exit pairing mode, as if pairing has been unsuccessful – i.e. I waited for pairing-mode to time out on the mouse.

And then what followed, was that the mouse works, and that the GUI shows me that data is being exchanged steadily. After I have done this, the pairing is successful and apparently stable! :-D

What this also tells me, is that I could have kept using the old dongle… :-( But then again, the new dongle has USB 4, which the old one didn’t! :-)


BTW, This is a kind of BT mouse, that does not require we pair using a PIN. The GUI has a separate button for that.



Bluetooth Dissed

One argument I hear often from laypeople, is that they don’t like Bluetooth, because at the user-level, Bluetooth Pairing is hard.

People who are knowledgeable in Computing understand, that every time we create a Bluetooth Pairing, our devices are establishing a communications channel, which is as secure as the authors of Bluetooth can make it, due to Advanced Encryption. So we see that there is a potential benefit to this.

For example, in the case of a keyboard which is connected to a tablet – which means that a BT session is underway – it can happen at any time, that we type in our password to unlock the tablet, or to unlock any of our accounts on the Internet. That could be made a generic wireless link which is extremely easy to set up. But then, since we’re always weary of an eavesdropper, the link would be of an ideal format, to steal all our passwords from us through direct exploitation.

But because we’re using Bluetooth, in fact it’s an encrypted link. So even if the ones and zeroes that make up a communication were intercepted, the hypothetical eavesdropper would still not be able to exploit them.

And so I can empathize with knowledgeable people, who feel that the added difficulty in establishing a Bluetooth Pairing, is well worth the effort.

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