Monthly Archives: August 2013

Review: Innergie PocketCell pocket battery charger: elegant design though limited capacity

Smartphone battery life has marched backwards, or so it seems: my ancient HTC Desire still lasts longer on a full charge than my newer Nokia Lumia 620 or Sony Xperia T. Another problem is tablets: battery life is decent compared to a laptop, but it is easy to get caught towards the end of the day or on a plane with an exhausted battery.

The solution, if you cannot get to a charger, is one of those pocket chargers for topping up your device. These are popular promotional giveaways, which means I have a drawer full of them (or would if I had kept them); but many are rubbish: bulky, fiddly with lots of assorted adapters to cope with different phones, and some with pointless adornments like solar panels.

I make a partial exception for a PowerTrip charger I received recently, which has an impressive 5700mAh battery, but it is still ugly, comes with three cables, and has silly extras like a solar panel and ability to work as a memory stick.

By contrast, the Innergie PocketCell is the first charger I have seen which has immediately impressed me with its design.

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There are only two pieces you need to carry with you, the small battery pack itself and a clever three-in-one cable in which the adapters snap together, so you can charge a device with Mini-B or Micro-B USB (the two popular types), or an Apple 30-pin dock connector (if you have an iPhone 5 or another device with the new Lightning Connector you are out of luck unless you have an adaptor).

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The same connector also serves to charge the PocketCell, using one of the many USB mains chargers you almost certainly already possess, or by plugging into a PC or Mac. The PocketCell has a USB Type A socket for output, and a Micro-B for input, so you cannot easily get it wrong.

On the side of the PocketCell is a button which you press to discover the current charge. It lights up to four LEDs, to indicate the level of charge remaining.

Battery capacity is 3000 mAh; not as good as a PowerTrip, but decent considering that it is less than one-third the size and much lighter (72g/ 2.5oz).

I tried the PowerCell on an iPhone 4 with a fully expired battery (at least, expired to the point where it would not switch on).

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The phone charged successfully, during which time the PocketCell got somewhat warm, but with impressive speed of charge. After the charge the PocketCell was pretty much exhausted.

The PocketCell supports 2.1 amp fast charge, which means it is fine for charging an iPad or other tablets with USB power.

The small size, nice design, and effective charging of the Innergie PocketCell means this device might actually find its way into your bag. The downside is that it is more expensive (especially in the UK) than some other portable chargers with equal or greater capacity, but its elegance and usability is worth a bit extra.

While I recommend the device, check that 3000 mAh is sufficient for you before purchase. I have also heard that the three in one cable is a little delicate, though you can get replacements if necessary or use a standard USB cable.

 

Expanding the Raspberry Pi with PiFace and Pi Rack

The marvellous Raspberry Pi, essentially a cheap, small PC, is a great device for education or home projects like media streaming. Out of the box though, it is not ideal for controlling other devices other than by USB or ethernet. What if you wanted to to use it to operate a switch under program control? You can use the GPIO (General Purpose IO) header, but it is a considerable step up in terms of the electronics knowledge needed for success (and to avoid damaging your Pi).

Element14 has an answer to this in the form of the PiFace, which connects to the GPIO header and provides a range of inputs and outputs. To be precise:

  • 2 changeover relays. These switch a link between a central common pin and two other pins.
  • 8 open-collector outputs. You can use these as switches for an externally powered device.
  • 8 digital inputs. These detect whether a contact is open or closed.
  • 4 switches. These close the first four inputs when depressed.

Element14 kindly supplied a PiFace to me for review, along with another accessory, the Pi Rack, of which more in a moment.

The PiFace comes in a small cardboard box with a regulatory compliance leaflet and no other documentation.

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Here is a closer view:

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You can see the inputs at bottom left, the outputs at top right, and the relays on the right. The following diagram from the Element14 site shows the details:

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The PiFace fits on top of the Raspberry Pi. A rubber foot on the underside rests on the HDMI port relieving the strain on the GPIO connector. If you have a standard size Raspberry Pi case, it will no longer fit once the PiFace is attached, though you can still use the base of the case as I did for my tests. Note that by default the PiFace takes power from the Pi, though this has implications for the power supply you use, which must be 850-1400 mA for the model B Pi.

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On the software side, installation is either by downloading a pre-built Raspbian image with the software already in place, or by modifying your existing installation. I am using the soft-float Debian Wheezy build and chose the latter route. It is not difficult; just enable the SPI (Serial Peripheral Interface) driver by removing it from the modprobe blacklist, run an install script, and reboot. The scripts come from a github repository here.

The PiFace software includes a nice emulator which lets you operate the switches. I am not sure that emulator is quite the right description because it really does operate the switches.

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Being more of a software person than an electronics engineer, I set myself a simple task: to operate a light switch under program control. I used a child’s electronics kit to provide the light. First I tried using the relay, which was very simple: it is just a switch. Next I used one of the open-collector outputs which also worked once I had found out that the negative connection from my external 3V power supply connects to GND on the PiFace. Here is my light in action:

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Note the LED is lit on the output terminal indicating that the switch is ON. Rather than the external supply, I could have taken 5v from the PiFace. A very simple test, but if you can switch a bulb on and off you can switch any number of other things as well, provided the voltage is not too great. Above 5v requires changing some jumper settings and even the relays should not be used for voltages over 20v or currents greater than 5A.

What about programmatic control? Libraries are supplied for Python, C and Scratch (a visual programming language primarily for education). I adapted the example Python script as follows:

from time import sleep
import piface.pfio as pfio
pfio.init()

while (not pfio.digital_read(1)):
if (pfio.digital_read(0)):
  pfio.digital_write(2,1)
else:
  pfio.digital_write(2,0)
sleep(1)

print "Bye"

This script loops until you depress (or otherwise close) the second physical switch or input on the PiFace. It reads the value of the first input, and if it is ON it turns on the output which lights the bulb. Rather pointless, but shows how easy it is to turn a physical device on and off under program control, and to respond to the value on an input.

I like the PiFace though it is in competition with the slightly more expensive Gertboard which has a motor controller, Digital to analogue and analogue to digital converters, and an on-board programmable MCU (Microcontroller). You might not need those features though, making PiFace a better choice.

A snag with the PiFace is that it uses the GPIO port and therefore prevents you using that port for anything else. In order to fix this and to increase the expandability of the Raspberry Pi, Element14 also supply the Pi Rack. This is a simple affair that give you four connections to the GPIO port. You can use this to operate more than one PiFace (each must have a different jumper-set address) or to use other GPIO devices such as the Pi Camera Module. The Pi Rack has its own 5v power input though no power supply comes in the box. Jumpers let you select which power supply to use on a connector-by-connector basis, and to swap the SPI CE (chip enable) lines if needed.

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Here is the Pi Rack in use with a PiFace. In practice you would want additional support for the PiFace rather than just relying on the connector.

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Currently the PiFace Digital is £20.30 and the Pi Rack £6.99.

Review: Bayan Audio Soundbook Bluetooth dock

The Bayan Audio Soundbook is a portable wireless speaker system for your smartphone, MP3 player, tablet or laptop. Oh yes, and an FM radio too.

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It measures 160 x 88 x 38 mm –  chunky for a portable unit, and at 530g not that light, though heavy is often good when it comes to audio. Not something for a pocket or small handbag, but fine to tuck in your case.

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The unit feels solid and has an unusual design. The front flaps down and folds back to make a stand, and the action of opening it also switches the device on. Hence the Soundbook name: open and play.

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This is a Bluetooth 4.0 device, and supports A2DP and aptX for high quality audio. Pairing your smartphone is a snap, with no codes involved. It also supports NFC (Near Field Communications), which worked well using a couple of Android devices I tried, a Nexus 7 tablet and a Sony Xperia phone. Just tap against the NFC logo on the underside of the flap, and a dialog appears to confirm the connection.

The Soundbook, in combination with your mobile, is also a speakerphone. There is a built-in microphone, and it behaves like a Bluetooth headset, pausing the music to let you take a call and resuming afterwards.

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You can also connect without Bluetooth, using an input on the rear. Finally, there is an output jack socket so you can use the Soundbook as a wireless input to your hi-fi.

Battery life is up to 10 hours for radio or wired connections, shorter if you are using Bluetooth.

The USB power connector is the Mini-B type. A shame that Bayan did not choose the Micro-B standard which is now more common.

So how is it? It seems a lot of thought has gone into the design and the flexibility is impressive. The actual sound quality though is only so-so, thanks to the small 1″ internal speakers, and lacking in bass despite a 2″ passive bass radiator. It is stereo, though you will not notice unless you are very close and I wonder if Bayan should have borrowed an idea from Logitech’s excellent Squeezebox or UE Radio, and gone for mono. At maximum volume it is pretty loud though rather strident.

Still, this is all a matter of expectations. It is miles better than the tinny speaker built into your smartphone or tablet, and the speakerphone feature is useful.

The FM radio is not too good unless, perhaps, you are particularly close to the transmitter. Bayan says there is “an advanced integrated FM antenna” but in practice I found it difficult to get decent reception other than for a couple of local stations, and even then only after careful placement. There are no presets; you have to press and hold tune up and tune down buttons to scan for channels, which is inconvenient.

You cannot switch between Bluetooth sources other than by disconnecting the current source in order to connect another. However, it will remember up to 4 pairings at a time.

Pros and cons

The Bayan Soundbook is nicely designed and supremely flexible. I particularly like the speakerphone capability, which means you can stick this on your desk, enjoy the music, but still take hands-free calls.

That said, if this is a device for a desk, Bayan should have made it a bit larger and bumped up the sound quality.

This is best for portable use then, for which it is not bad, though a little bulky and heavy. I could more easily forgive that if the sound quality were just a bit better.