begriffs

DIY Backpack Base Station

January 4, 2016

Crazy backpack

Wouldn’t it feel great to compute comfortably anywhere, impervious to poor coworking conditions? Forget slouching over a tiny laptop in a coffee shop, hunting for an outlet and jumping through hoops for shoddy WiFi. Imagine instead arriving at a coffee shop in a blaze of your own portable electrical power and high speed internet. By filling a backpack with the right gear I think you can create a productivity force field.

Electricity

If your laptop is the brain of your base station then a battery is its heart, pumping nutritious electron blood. The problem is your mobile devices were all designed with size limitations which limit the size of their batteries. A backpack base station removes this limitation. Let’s pack it with the heart of an ox, a big rechargeable battery.

When choosing a battery we want two things

  1. A large amount of total energy (measured in joules)
  2. Output at the correct voltage with sufficient amperage for our devices

Batteries for computers and phones come with attached DC power converters, and the battery+converter duo is called a portable charger or power bank. Their available energy is confusingly advertised in milliampere-hours (mAh) which is of the same dimension as the coulomb. The confusing part is that mAh is always relative to an output voltage, typically the 3.7 volts of the model 18650 Li-Ion batteries that are so often inside external chargers. This convention inflates the mAh number actually relevant to you since computing devices need more than 3.7 volts to operate – even little old USB is 5V.

We’re looking for a battery with lots of energy (properly measured in joules). A unit more common in the battery world but with commensurable dimension is Watt-hour. For our base station backpack I’ve found a real beast, the BiXPower CP300 with 300 Watt-hours. It can output at any of 12, 15, 16, 18.5, 20, and 24 volts.

Different models of laptop require different inputs. For instance the maximum voltage supplied by Apple Magsafe power bricks are

Voltage Supplied with
14.5 V DC / 45 W MacBook Air
16.5 V DC / 60 W MacBook and 13" MacBook Pro
18.5 V DC / 85 W 15" and 17" MacBook Pro
20 V DC / 85 W 15" MacBook Pro Retina

The battery weighs five pounds and measures 10.5 x 2.2 x 6 inches, which leaves plenty of room in a big backpack. What’s the next organ in our body informatic?

Networking

Our goal is fast private internet access anywhere with no worries about the presence or quality of the WiFi of our physical location. Hence we should go cellular.

Once again we have a backpack to work with, not the limited form factor of phones or computers. We can choose dedicated high quality networking components. This also gives the advantage of being able to upgrade or replace individual logical parts in a way that is not possible with all-in-one consumer devices.

We’ll start with a dedicated 4G LTE USB Modem (also known as an aircard), the Pantech UML295. The modem is great on its own but no self-respecting base station would be complete without a sick 8 dBi high gain antenna. This footlong antenna operates discreetly from your magic backpack. Nobody is the wiser, but your network is the faster.

You and anyone else in your wireless posse will access the 4G network through a dedicated wireless router. The TP-LINK TL-MR3020 is perfect for the role. It is a precise tool, able to create a hotspot through 4G or a wired connection, or to bridge an outside wireless network. Plus it’s tiny, at 2.1 ounces.

Being a single purpose tool, it does not try to include its own battery. This allows it to work nicely with the central battery. The router consumes five volts at one amp through mini USB. Luckily in addition to its main DC output our central battery includes a 5V USB socket. Assuming the router operates constantly at a full five watts, our 300Wh battery can run the whole 4G connection and WiFi hotspot for sixty hours straight. That’s days of solid internet access from any location.

Travel Peripherals

For more display area and comfortable pair programming get a lightweight USB travel monitor. The AOC e1659Fwu is sixteen inches and 2.4 pounds. It has a little kickstand like a picture frame and gets all its power from USB. Lift your laptop to a good viewing angle next to the travel monitor with the Cosmos angle stand. It folds up small and weighs seven ounces.

Finally if you really want to get weird, there’s this fold up travel standing desk with telescoping legs, the Tabletote. It’s three pounds and folds into a rectangle 13 x 10.5 x 1.5 inches. It even comes with an unlikely document holding arm.