Smartphones Archive

Gadget List–Essential smartphone and tablet accessories

You have just bought that new smartphone or tablet and want to make sure it is complete when it comes to accessories. These are about charging that “do-it-all” device up or running it from external power; connecting the device to other devices like speakers or car stereos; or simply allowing you to operate your device safely and protecting it from unnecessary damage.

Power supply

Each charger should have at least one USB Type-A socket so you can connect the smartphone, tablet or other mobile device to it via its USB data cord. Some devices that use a DC plug or other connection form can be connected to these chargers using a USB power-adaptor cable which may come with the charger or can be picked up as an accessory.

As for power capacity, I would recommend using a charger that works at 2.1 amps if you are using a tablet or are likely to charge two or more devices at once. It is also worth noting that you can use a charger as a way of powering the phone or tablet in a manner to conserve battery runtime. This comes in handy when you are, for example, using your phone for navigation or music as you drive or using a smartphone as a network access point.

AC-USB charger

AC USB charger

AC-USB charger

You never can have too many of these chargers especially if you need to top up a phone or tablet that is always running out of juice or being used heavily.

The small USB chargers can be useful as part of a small accessory bag that you take with you when you travel, even as you go out and about. Similarly, there are the USB chargers that have an integrated AC socket as well as the USB sockets. These are very handy if you come across situations where lamps and appliances are constantly unplugged by people wanting to charge up their smartphones or tablets or run these devices at home without compromising their battery runtime.

On the other hand, a self-powered USB hub with its power supply can serve as an AC-USB charger for up to four or seven devices.

Cigar-lighter-USB car charger

USB car charger

USB car charger which plugs in to a vehicle’s cigar-lighter socket

The USB car chargers that plug in to a vehicle’s cigar-lighter socket can be very handy whether you drive a vehicle or not. In some cases, they can come in very handy with other accessories that work on the same voltage such as Bluetooth audio adaptors and most of these are as big as a thumbnail thus not occupying much space in your accessory bag.

External battery pack

USB external battery pack

USB external battery pack

These accessories come in two forms – a rechargeable battery pack that is charged by a USB connection or a battery holder that takes two to four AA batteries and converts the power from the batteries to USB power for your phone.

There are variants of this device that are designed for the older Apple iPhones which use the legacy 30-pin dock connector. Here, these units can be charged from an Apple-compliant dock and be clipped on to the iPhone they are to power. Further variants of this device come in the form of a case that the iPhone sits in rather than a battery pack that clips on to the iPhone.

Similarly, some of the rechargeable battery packs may use an integrated or accessory solar panel to allow you to charge them from the sun. These typically are to allow you to operate your phone independently of the AC power and are sold on an “eco” or “green-living” promise, but they take a long time to charge up fully from the sun and require the charger to see bright sunshine.

Lower-capacity devices may work well for charging up a smartphone once or “boosting” (adding power) to a 5” smartphone or tablet. This is compared to higher-capacity devices which could charge up a smartphone two or three times or a tablet once or twice; or simply be effective in providing “long-run” power to the smartphone or tablet.

It may be worth noticing with some of the rechargeable battery packs that have two or more USB output sockets in that if they are connected to a charger and switched on, they could supply power to two or more devices. This can come in handy if you want to cut down on the number of AC or car chargers you take with you.


USB data cables

USB data cable

USB data / power cable

This cable is essentially how you get power in to your phone or tablet and it should have a Type A USB connector on one end and the connector that fits your device on the other end. This typically will be a MicroUSB connector for most non-Apple devices, a 30-pin Apple Dock connector for older Apple devices or the small Lightning connector for new Apple devices. You could get by with one or more cables that have the Apple Dock connector and some Dock-Lightning plug adaptors if you have a mix of Apple devices that have the different connectors.

Audio connectivity

For any portable audio device, I consider the following cables as essential to keep with the device:

  • A cable with a 3.5mm stereo mini phone plug at each end
  • A cable with a 3.5mm stereo mini phone plug at one end and two RCA (phono or cinch) plugs at the othe end
  • A cassette adaptor which slots in to car cassette players and connects to your phone or tablet
3.5mm to 3.5mm stereo audio cable

3.5mm to 3.5mm stereo audio cable

The first cable comes in handy with an increasing number of car stereos, home-theatre receivers and other AV devices that use a 3.5mm (1/8”) mini phone jack on the front. This is to allow you to walk up and connect portable audio devices to these units and have them play through the system’s speakers.

3.5mm stereo to 2 RCA plug audio cable for most audio equipment

3.5mm stereo to 2 RCA plug audio cable for most audio equipment

The second cable comes in handy with connecting your phone or tablet to just about every piece of home audio equipment, including some mid-range and higher-end “ghetto blasters” made through the 1980s and 1990s just by using any vacant line-level input i.e. a “tape”, “CD”, “tuner” or “aux” input.

Cassette adaptor

A cassette adaptor that allows you to use your smartphone with a cassette-based car stereo

Some of you may see the cassette adaptor as a dated accessory especially with an Apple iPhone but it still has its place with your smartphone or tablet. For example, you may be using a late-70s / early-80s classic car that is kept “true to its era” and have tracked down and fitted a cassette player or retained the factory-supplied cassette car stereo in the dash of that car to keep the car that way. Similarly, some of you may have kept a cheap old car radio-cassette stereo with that “fast-forward / eject” button in that old car because you are in a risky neighbourhood and a nice car stereo would be asking for a brick through the window. You may also deal with a late-80s or mid-90s car that has an integrated cassette car stereo and you can’t substitute it easily with aftermarket car audio equipment. Here, the cassette adaptor effectively converts the cassette mechanism, hence the cassette slot, in to an auxiliary input through the use of a head mounted in the adaptor that inductively couples with the cassette player’s playback head to pass the sound to the player’s amplification circuitry. This means that even if the mechanism was prone to “chewing” the tape when it played tapes, it can work with these cassette adaptors.

Realistic car stereo radio-cassette (12-1892) - 1981 catalog shot -

With a cassette adaptor, you can play your smartphone or other device through this old car stereo

Other accessories

Removable windscreen mount

Another accessory that I find very important for smartphone users is the removable windscreen mount. Here, this device “grips” the phone and sticks to the windscreen (windshield) using a suction cup so you have the phone in a stable position. This is important when you are using the phone with a good maps app for navigation, as a music player / Internet car radio, or want to be sure whether to answer that incoming call when it rings. The fact that you can remove the removable windscreen mount is important if you need to take your device between cars that don’t have a phone mount, such as rental or borrowed vehicles, or want to conceal the phone mount thus avoiding the chance of your car being broken into.

Bluetooth audio adaptor with microphone.

Nokia BH-111 headphone adaptor connected to headphones

Now these good headphones or other audio device can work as a stereo Bluetooth headset for your smartphone with a Bluetooth audio adaptor

A device that can come in very handy with any smartphone or tablet is a Bluetooth audio adaptor like the Nokia BH-111 or a recently-issued Kogan Bluetooth adaptor. These devices effectively work as Bluetooth handsfree kits by supporting headset or hands-free operating modes as well as the A2DP media-streaming operating mode, but are connected to headphones or external audio equipment for their audio output.

This can be handy with temporary setups where you want handsfree telephony or audio playback through existing equipment such as with home or portable audio equipment or rented or borrowed cars.  For car use, they may be best secured to the middle of the dashboard with double-sided tape or a good amount of Blu-Tack.

A lot of these devices will have an integrated microphone so you can speak to your caller during that call. There may be some good Bluetooth portable-handsfree kits which have an integrated speaker that may also have a 3.5mm stereo mini phone jack as an audio output especially when streaming music content from your device. This kind of setup may feed the Bluetooth Headset / Hands-Free Profile audio to the integrated speaker and the Bluetooth A2DP stereo audio to the external device.

Wraps or covers for your device

Any of the wraps or covers that are available for your particular phone or tablet work well in protecting the device as well as conveying your sense of style to your device. Some can range from a simple vinyl finish to a luxurious leather finish which has that look of that special wallet and, of course, the more you pay the more likely it will last for a long time. But, if you use an NFC-capable Android phone or tablet, you have to make sure that the wrap or cover doesn’t interfere with the NFC functionality. Similarly, you may find your Android device thinking it has cottoned on to an NFC device if you store your “touch-and-go” transport card or security pass in your billfold-style device cover with your device.


When you equip your smartphone or tablet with these accessories, you have the ability to gain more flexibility out of your mobile device. This is whether to avoid compromising your device’s battery runtime or have your device highly available; or to make it work with a wide range of computer or audio equipment; or simply be able to use the device safely and protect it from damage.

Send to Kindle

Smartphone cameras and compact digital cameras–how I see them


Smartphone Cameras v Point And Shoot Digital Cameras | Photography

My Comments

Often we think of the cameras that are integrated in the typical smartphones as competing with the traditional compact digital cameras. Typically the smartphone and tablet cameras win out on integration in to the device we carry around frequently and immediate access to the online world for sharing what we have taken, whereas the compact cameras, especially those modelled on the 35mm compact camera, win out on the body shape, optics, sensor and electronics being tuned for the act of photography.

Taking images further

The main obstacle was taking the images that you took with the camera further using mobile-computing apps and Web sites. This is to do things like “throw” a copy of that image you took to the subject for them to take further or simply to share that image with your friends via Flickr, Picasa or Facebook.

Some newer trends have occurred where the cameras have been equipped with Wi-Fi wireless, Bluetooth or integrated wireless broadband in order to facilitate sharing of images held on the camera. The connection is augmented with front-end apps for image-sharing, cloud-storage and social-network services installed on the camera. There are even a few cases of digital cameras which have the Android mobile operating system as their operating system, with access to the same Google Play app store as you would have on an Android smartphone. This setup allows one to use the apps that exist for the Android platform such as the Dropbox and Facebook mobile front-ends with these cameras.

It is to mitigate the common situation where images have to be downloaded to a computer before they can be shared, whether through the camera being “tethered” to that computer or one removing the “film” i.e. the memory card from the camera and inserting it in the computer.

On the other hand, those of us who have newer Android smartphones and tablets could use a USB “On The Go” cable and either the camera’s USB cable or a card reader to “get at” the images we took with our cameras. Similarly Apple sells an iPad accessory kit which offers this similar function for the iOS devices.

Similarly, cameras that work with the “Eye-Fi” cards can allow you to share the images to your smartphone or tablet so you can take them further with the apps on these devices. They could utilise mobile NAS units of the likes of the Seagate GoFlex Satellite or the Kingston Wi-Drive as extra storage for the images and footage.

How I see this

I see the compact digital cameras existing as a way for those of us who value good-quality images to take these images on the go, including working as an auxiliary camera for big-time photographers.

Whereas the smartphone cameras would work more like the entry-level “quick-snap” cameras of the ilk of the Kodak Instamatics, the Polaroid instant-film cameras and the fixed-focus entry-level 35mm cameras where the goal is simply to grab a quick snapshot of the moment. They would also serve as a tool to create images they can refer to when doing tasks such as dismantling an item or grabbing reference numbers.

Send to Kindle

Do you think we will end up with the smart watch on our wrists?


Why You’ll End Up Wearing A Smart Watch | Gizmodo Australia

My Comments

With the increase in smart watches being developed by various companies including Google, Apple and Samsung, there has been optimism and doubt about whether we will start wearing these watches on our wrists.

What is the smart watch?

The smart watch is an extended-function watch that works with a smartphone as a wrist-based display for the phone. These watches are in a similar vein to the 1980s-era digital watch where the more functions it had, the more you could impress others with it. In a lot of cases, these functions served many practical uses like being able to time a process or log the duration of events like races.

It would tell the time using a customisable analogue or digital display but would be able to show up notifications from your smartphone. As well as being the clock, calendar, stopwatch and timer, it could also work as a remote control for your smartphone such as navigating the music that you are playing, selecting a contact to call or text or answering a call while you hear and talk to the caller via a Bluetooth headset. Another advantage that these would offer would be the ability for us to have a discreet glance at the watch if a message comes in on our phone.

Some doubters suggested that the smartwatch wouldn’t take off because of the fact that most young people don’t wear watches anymore. Instead they use the smartphone to tell the time or, if they have to have a watch, they would wear a quartz-driven dress watch. Of course, I would expect to see the smartwatch be considered as a wearable accessory to the smartphone and can evoke a level of curiosity from other people as we wear one of these watches just like it did with the digital watch.

What I would expect of the smartwatch would be to make use of Bluetooth 4.0 and similar technologies so it can run for at least 6 months on regular watch batteries. This is in addition to having a ladies’ form factor with similar functionality but appealing for the women to wear.

As well, it should be able to keep time independently of the host smartphone device yet use that device as a master clock for setting itself when initially started and when you cross time zones or whenever we change between standard time and daylight-saving time.

Personally, I would see these watches come on the scene as a viable practical mobile accessory for our phones rather than just a fashion accessory.

Send to Kindle

Google Maps has now come back to the iPhone


Google Maps is now available for iPhone | Official Google Blog

App Store location

Google Maps

My Comments

Previously, people who used the iPhone or iPad had the Google Maps provided as an integrated mapping solution for their devices. Then, when iOS 6 was launched, Apple decided to pull the Google Maps from the operating system and substitute it with a poor-quality mapping solution.

This has led to situations like people ending up in the wrong location and nearly dying, and the Victoria Police advising against using Apple Maps because of this poor-quality mapping.

There was so much criticism of this mapping solution that Apple had to bow to public demand and create an app group for third-party mapping apps for their iOS devices. Now, the Google Maps mapping solution has been made available to iOS 6 users through a downloadable app. This has the advantages of the Google Maps such as vector-driven maps, 3D views, turn-by-turn navigation and Street View but ported to the iOS platform.

For those of you who are still working with that trusty old iPhone 3GS, this app can work with that phone. Infact, any of you who are updating an iPhone or iPad to iOS 6 should infact factor in deploying Google Maps along with YouTube on the device as part of the update plans in order to gain the full benefit of these popular services on that iDevice. Similarly, when you buy that new iPhone or iPad, it may be a good idea to make these apps your first downloads from the App Store as part of commissioning that new device.

Send to Kindle

Why purchase as much storage capacity as you can afford when you buy a computing device

Toshiba Tecra R950 business laptop

Toshiba Tecra R950 business laptop

Very often, I notice people who are buying a computer, tablet or similar device purchase the device based on the price without thinking of the issue of the unit’s secondary-storage capacity.

But in most situations, the cheaper variants of these devices have lesser storage capacity. This may not be an issue if the device is serving as a secondary computing device and you are likely to either use a auxiliary storage devices like external hard disks, removable SD cards or cloud-hosted / network-hosted storage with the device regularly. What can happen as you use that iPad or laptop is that the main storage capacity fills up and it feels as though there is a noose around your neck as there is less storage capacity on your device for you to store programs or data. In some situations, the device doesn’t perform as well as it should.

You also think of having to frequently purge your system of data that may be “put away” but is to be on hand for use at a later time. In some cases, this activity may cause you to dump data that you may later regret dumping.

Toshiba AT300 10" Android tablet computer

Toshiba AT300 10″ Android tablet computer

But you can avoid this with new computing devices especially those you expect to use as your main computing devices if you buy or specify as much storage capacity as you can afford. For example, I encouraged someone who was in the market for an iPad to think of the higher-capacity models because people tend to have them full of photos, music, email and apps very quickly.

In most cases, your device’s storage capacity can be a key bargaining point when choosing that device. For example, you may have something of AUD$100-200 between one storage class and another more capacious storage class for a tablet or a laptop. Some dealers may also try to offer the variant with more capacity for the same price as the model that you are after and have budgeted on.

There is also a reality that as time passes on, the cost of data storage does reduce for a particular capacity due to Moore’s Law.

So if I buy or specify a computing device for someone, especially if the device is expected to be a main or sole computing device, I would make sure that there is as much hard disk, SSD or other storage space as you can afford.

Send to Kindle

Google-written YouTube client for the iPhone now available from the App Store


YouTube releases standalone app for iOS, tablet-tailored version in the works – Engadget

From the horse’s mouth

Introducing a new YouTube app for your iPhone and iPod Touch | The Official Google Blog

iTuned App Store Download link

My Comments

Apple are intending to remove the integrated YouTube player from iOS 6 as part of “stripping off” all things Google from the iOS platform. But Google have responded by developing a standalone player to be distributed through the iTunes App Store.

The version that is currently being premiered is pitched at iPhones and iPod Touch devices but Google are working on a “large-screen” version that is pitched at the iPad tablet.

There is an Integrated user interface for content discovery, where one can browse or search for videos. This includes access to the YouTube Channel Guide as well as an improved search-as-you-type engine. Even the ability to share YouTube videos through the “usual suspects” (Google+, Facebook, Twitter and email) has been improved.

The repertoire of videos avaliable to users with this YouTube client has increased, with users being able to view the Vevo music-video library like most of the clips that defined music video in the 1980s like this Dire Straits clip.

Of course, those of us who run iOS 5 on our Apple mobile devices could download this if we want the improved YouTube experience on the device. Also, this may provide a “coarse” user experience for the iPad until the iPad version is released.

Send to Kindle

Two-screen TV viewing a strong trend


The Future Of TV Is Two Screens, One Held Firmly In Your Hands | Fast Company

My Comments

There is something that is becoming a reality with TV. It is where our TV-viewing sessions are involving two screens – one large screen carrying the main video and one smaller screen that we are holding in our hands.

This has been brought about by the popularity of the tablet, laptop and smartphone which are serving the second-screen role.

Some of us may think it is just for checking email or the activities of our Facebook Friends or Twitter followers. But a fair bit of this activity is to do with the content itself.

For example, one could be using GetGlue, Fango or other TV-related social networks to find out who is watching this show and what others have to say about it. Similarly, one could be checking the show’s Website and looking at other information and commentary that exists there. These are activities that may not work well on the big screen.

Similarly, most big-screen applications cannot support multiple concurrent logins for social-network or similar uses; and they are typically require “pick’n’choose” or “SMS-style” text entry.

In the case of news, a good quote for this is that “the revolution doesn’t have to be televised”. Here, one could be checking other news resources to verify the veracity of a news story, which can be very difficult during election time. This is augmented through comment feeds and Tweet feeds that are set up during news events like the one I participated in during the UK parliamentary inquire in to the News Corporation phone hacking scandal where I was dropping Tweets in to the feed from a Fujitsu laptop that I was reviewing. Similarly the scoreboard apps that I have mentioned about previously could simply work as an always-live scoreboard display during a sporting event and some sports like cricket or racing may benefit from these apps further by displaying supplementary scores like track position or bowling scores.

Of course, the commercials as we know them will be hamstrung by the two-screen viewing experience. This is more so as the traditional goal of eyeballs at the screen during ad breaks is reduced more. Here one could be following up information on the second screen while the ads play on; as well as visiting the kitchen or bathroom or stoking up the log fire. But the information that one could be following up on can relate to what was in the TV program; or it could be to follow up on something that was advertised during that ad break or a previous ad break.

As I have noticed and observed, this concept of two-screen TV is hard to adjust to for some people, especially the older generation who are more interested in focusing directly on the screen. It may be us simply glancing down at that smartphone or tablet so we can know further what is going on with some events.

I see this as becoming an interesting chain of events as we integrate in to an online and highly-interactive media-consumption life.

Send to Kindle

Repost–USB Audio in Android Jelly Bean to mean more in the way of accessories

I am reposting this to make sure that the link to the product review is working properly for RSS, email and Facebook subscribers


Gear4 speaker dock supports USB audio for Jelly Bean at Google I/O 2012 (hands-on video) — Engadget

My Comments

Sony CMT-MX750Ni Internet-enabled music system main unit

An iPod-enabled music system that can also benefit from Android’s new USB Audio interface

Apple iOS users have had the advantage of also having a USB single-wire or docking connection between their iOS device and accessory equipment, with the ability to channel the sound data, the control signals and power to their device using the same connection. This has built up the iPod / iPhone accessory market very strongly with the accessories allowing the user to start and stop the music or move between tracks and folders on their iPod or iPhone using the control surface that the accessory provides.

People who used Google Android devices were limited to an analogue or Bluetooth audio link between an amplification device and their smartphone or tablet with support for transport control if the phone was connected via Bluetooth. They typically had to run a separate USB cable if they wanted to supply power to the Android device from that accessory.

Now the latest iteration of the Android platform, known as “Jelly Bean” and version number 4.1, supports USB Audio. This is similar to how a USB speaker system or external sound card can work with most desktop operating systems. It can then allow a large manufacturer base to develop “Android-friendly” audio playback equipment like speakers, Internet radios and hi-fi amplifiers / receivers in a timeframe that allows the device to be “ready-to-market” quickly.

What could be looked at

Communications audio

There are some questions I have about this kind of setup. One is whether the USB Audio functionality in Android Jelly Bean can allow for communications audio as well as audio content from the media player program. This would be of importance with automotive applications where the USB Audio link could be used as an alternative to Bluetooth for hands-free telephony in the car.

Device control

The other issue to look at is exposing the accessory device’s control surface as a control point for the Android device’s communications and media-playback functions. This situation would be of importance for accessory devices which have other audio or video sources like broadcast tuners, optical-disc players or USB Mass-Storage device connection. In the automotive context, it also extends to nearly all car infotainment setups that allow the user to make or take a call using the controls on the dashboard.

Here, it could be feasible for the accessory to control the media player or phone user interface using either the screen on the Android device or using the controls on the accessory. Here, it could allow for “basic” transport control and metadata display on the accessory device while advanced “search and play” can be performed on the Android device. Similarly, call-progress control can be managed using controls on the dashboard with the ability to, when the car is parked, commence a call on the Android device’s touchscreen.

Similarly, MirrorLink or similar techniques culd allow the accessory device to be configured or controlled in an advanced manner using the touchscreen on the Android device. It could come in handy with A/V equipment which may need specific configuration and setup procedures or Blu-Ray players that may expose “second-screen” interactivity functionality on the handset.


At least, Google have integrated commonly-accepted open standards to add functionality to Android in a manner as to rival the established Apple mobile-device platform and stimulate a healthy competitive design environment.

Send to Kindle

DLNA now part of Nokia Lumia WP7 phones with Play To app


Nokia’s Play To app now available for Lumia devices, enables DLNA-connectivity – Engadget

“Play To” DLNA App for Lumia’s Already Available in Marketplace | My Nokia Blog

My Comments

A feature that Microsoft should have provided as part of the Windows Phone mobile operating system but provides as part of the Windows 7 desktop operating system is the “Play To” function. Here, it allows you to push pictures, audio content or video content from your device to a DLNA-compliant network media player that can be controlled by other devices.

A question I have pondered about this operating environment is whether one could play content held on the phone or on a DLNA-compliant network media server through that smart TV or network-capable home-theatre receiver using one of these phones. Now the question has been answered with this app being available for the platform.

But, personally, I would like to see this available on the Windows Phone MarketPlace as an app for any WP7 phone and work in a “full” manner with network and local content. This means that it could download content from a DLNA NAS to the phone, play out content to a DLNA device, upload photos and video content to a NAS with DLNA upload functionality as well as cause content held on a media server to be played on a media-renderer device. This could them prove the Windows Phone 7 as part of the industry-standard media management landscape.

Send to Kindle

A vehicle hands-free kit offering access to apps on your iPhone


Clarion Next Gate hands-on (video) – Engadget

Clarion Next Gate puts iPhone control, app integration on your windshield | CNet Reviews

Clarion Next Gate brings iPhone apps (and distractions) to your windshield | Engadget

My Comments

The CTIA mobile-technology show in the US has become a launch-pad for Clarion’s “Next Gate” car hands-free kit.

The kit works in a similar manner to Pioneer’s “AppRadio” concept, where an iPhone that has a specific handler app is connected to the car-audio system and selected apps are exposed to the car-audio system’s touchscreen display and control surface.

But this unit implements it in the form of a “walk-up” hands-free kit that has the main unit temporarily mounted in the car and powered from the vehicle’s cigar lighter and connected to the auxiliary input of an existing car stereo. 

There are a few questions that need to be answered concerning these car-audio setups. One is why the device doesn’t support a Bluetooth device class or application to permit this kind of “remoting” of specific applications held on a platform smartphone, such as Internet-audio, navigation and traffic-information apps from an external control surface. This may help with people who may not want to bother cabling up the smartphone to this device.

Of course there is already a standard available to the market for this kind of remote control of smartphones from a dashboard-based control surface. This is in the form of MirrorLink, valued by an increasing number of other vehicle infotainment companies operating in the OEM and aftermarket space, and Samsung is running with this standard in their latest Galaxy S III smartphone.

But Clarion and Pioneer may prefer having these devices work as a discrete user interface to the apps themselves and the data they expose rather than the phone as a device. This may provide the ability for the device manufacturers like them to have greater control over what apps appear on these devices.

If the direct-app-link approach is preferred for vehicle-smartphone integration rather than the “terminal” approach offered by MirrorLink, the industry could work on a standard for facilitating this kind of link.

Send to Kindle