On The Road With A Powerocks Magicstick Extended Battery

Highly Recommended

Just back from a quickie business trip – my first with a Powerocks Magicstick 2800 universal extended battery for my phone. When I travel I’ve always been careful about phone use just in case I need to make an emergency call, check for an important email, text etc.  I never seem to be able to find an electrical outlet when I need one. The Magicstick eliminates these worries. 

I’ve been reading Leander Kahney latest book on Jonathan Ive, the head of Industrial Design at Apple. It’s really opened my eyes to intuitive design, simplicity and absence in clutter. The Magicstick has that Jony Ive / Apple feel. It comes in a bunch of different colors (mine is black) and includes a micro-USB-to-USB cable for charging up the Magicstick and a nice little bag to keep it in. 

It’s a small (sort of reminds me of a BIC cigarette lighter at 3.5” long, and 7/8” in diameter) 2800mAh portable battery that you pre-charge using an included micro-USB-to-USB cable. When it comes time to charging the Magicstick you just plug the charging cable in and charge it up. When you want to charge your phone or other portable device you just plug the cable that came with the phone or other device into the Magicstick standard USB port. On the opposite end of the Magicstick there is a smart push-button LED that shows charge status. Blue light = 70% - 100% full, Green light = 30% - 70% full, Red light = 1% - 30% full. 

I was able to get two charges on my old iPhone 3GS (from approx. 20% to 100% and yes I still have an old iPhone) with one fully charged up Magicstick. It will charge Apple, Samsung, Nokia, Motorola, Blackberry, etc, etc, etc devices - basically anything that will charge using a USB connection.  Simple.

A nice little stocking stuffer, grab bag, office swap gift, birthday present, etc - The Captain and I give it our highest rating of 5 out of 5 Gordoccinos.  

You can get more info on the Powerocks website. 

Attenuation in Fiber Communications Systems

I'm teaching a fiber optics communications course this semester and - like just about every communications course - we started out talking about attenuation.

Attenuation is just a fancy word for loss. In any communications system you've got a certain amount of signal strength going in and a certain amount of signal strength coming out. If there is no amplification in a system there is always going to be loss and the output signal will always be weaker than the input signal.

In fiber systems attenuation is caused by three things:

1. Absorption - Glass, whether it is fiber or the windows in your house, will always absorb a small amount of light going through it. The amount depends on the wavelength of light and what the glass is made of.
2. Scattering - Atoms in glass cause a certain amount of scattering of light and scattered light will not emerge at the output.
3. Leakage - Light will leak out of fiber, especially if the are a lot of bends in the fiber.

Fiber manufacturers typically provide specifications for all three of these, along with total attenuation per kilometer.

One of the primary goals in any communications system is to keep the attenuation to a minimum. Even so, there will always be a loss in signal intensity when comparing output power to input power. Calculating attenuation in a system is pretty simple. Attenuation is cumulative so basically you just add up the signal loss for each component in the system. Here's an example:

Question: A 50 km fiber run has been spec'd at 99% transmission per km. What percentage of light will emerge at the output?

Answer:

The fiber run is transmitting 99% per km so after the first km 99% of the input signal will be available, after the second km, 99% of what's left after the first km will be available, etc. So we can say:

60.5% of the original input signal strength will emerge at the output.

What The Heck Is A Decibel?

Maybe "decibel" is not part of your normal vocabulary but it is a term we all occasionally read or hear used. Typically it has to do with noise levels - we use decibels to describe loud or soft sounds. US government research even suggests a safe exposure sound limit of 85 decibels for eight hours a day. We frequently hear the term but - have you ever wondered what a "decibel" really is? Let's take a look.

Decibel (abbreviated dB) measurement is a logarithmic measurement typically of a output/input ratio of power or voltage. According to Wikipedia, the decibel originates from methods used to quantify reductions in audio levels in telephone circuits. Over distance any type of transmission media (copper wire, fiber optic lines, wireless) signal gets lost. The simplest way to think of a transmission system is as a box with signal going in and signal coming out the other end. In the diagram below we'll use P_in for our input signal and P_out for our output signal.
P_loss in the diagram is the power lost as the signal moves from the input to the output of the system. Any communications system signal is going to lose strength as it moves from one point to another due to things like resistance, capacitance and inductance that are all integral parts of any transmission system. Heat (as in hot days) can be a major problem for cable and telephone companies because wire resistance increases with heat causing more power to be lost in the delivery system. Sometimes signal loss is so significant amplifiers have to be added to a communications links to clean up and boost signal strength. Let's take a look at how decibels are calculated.

Power loss in dB is calculated by multiplying 10 times the base-10 log of the output power (P_out) divided by the input power (P_in). Let's look at an example where P_in is 20 Watts (or 20W) and a P_out is 15W.

P_loss in dB = 10 x log₁₀(P_out/P_in)

P_loss in dB = 10 x log₁₀(15W/20W)

P_loss in dB = 10 x log₁₀(.75)

Using a calculator to take the base-10 log of .75 we get -.125 Don't miss the negative sign - it is important here - it indicates power is being lost in the transmission system. Continuing with our equation.

P_loss in dB = 10 x (-.125)

P_loss in dB = -1.25dB

So, in this transmission system example, our output signal is said to be down (referencing the negative sign) 1.25 dB.

Let's work one more calculation, this time using a P_in of 16W and a P_out of 8W. Not a very efficient transmission system if we are losing half the power we put in. Let's see what we get for decibel loss working through the equation.

P_loss in dB = 10 x log₁₀(P_out/P_in)

P_loss in dB = 10 x log₁₀(8W/16W)

P_loss in dB = 10 x log₁₀(.5)

Using a calculator to take the base-10 log of .5 we get -.3 Again - don't forget the negative sign. Continuing with our equation.

P_loss in dB = 10 x (-.3)

P_loss in dB = -3dB

In this example, the system is losing half the input power and our output signal is said to be 3dB down. This is important to remember - for every 3 dB power decreases or increases by 50%. How do we know if it is increases or decreases? By that very important positve or negative sign!

In a future post we'll take power calculations a little further and discuss something called the dBm Scale.

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Update 01/25/10

Homework: If P_in is 7W and P_out is 5W what is the P_loss in dB?


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Power Supply/Charger Energy Waste Explained

I've had a few people recently ask me about power consumption by vampire devices in their homes - most specifically about power adapters for devices with rechargeable batteries like laptop computers, cell phones and iPods. The typical question is along the lines of:

I hear these things still draw power when plugged into a wall outlet even though the device (iPod, cell phone, etc) is not attached. Is that really true?

My answer is typically YES! These external supplies have transformers and some rectifier circuitry in them that convert alternating current (AC) voltage to direct current (DC) voltage. A schematic of a simple DC power supply/charger is diagrammed below (click image to see larger and clearer version).Here's how they work:

1. The power supply/charger is plugged in to wall.
2. AC current flows through the primary coil in the transformer and creates a magnetic field. This magnetic field from the primary coil is coupled into the secondary coil. The transformer is used to step down (reduce) the AC voltage by adjusting the number of coil wire turns (turns ratio) in the primary and secondary coils.
   
3. The rectifier circuitry takes the AC voltage from the secondary coil and flattens it out into a non-oscillating DC voltage that portable devices can use for power and battery charging.

If you take a close look at the diagram you will notice AC current flows through the primary coil as long as the power supply/charger is plugged into the wall. Notice the device (laptop computer, cell phone, iPod, etc) does not have to be attached for power to be consumed and effectively wasted.

How much power is wasted by vampire devices like these? The U.S. Department of Energy estimates 5% of all electricity used in the U.S. is consumed by devices in standby mode and predicts this will increase to 20% by 2010!

What can be done? The simplest thing to do is unplug your charger when it is not actually being used to charge the device it was designed for. Another option is to plug power supply/charger devices into a switched power strip or electrical outlet, only turning power on when devices are attached.

We're also starting to see "smart chargers" for some devices that use some simple circuitry and only power up when a device is actually attached.

Going Green: Broadband over Power Line (BPL)

Stacey Higginbotham at Gigaom wrote an interesting article on Friday titled BPL Goes Green. In the piece she discusses how companies in the United States have shifted Broadband over Power Line (BPL) strategy from pushing broadband to providing demand response systems to electric utilities.

You may recall - in 2004 - the Federal Communications Commission (FCC) and venture capitalists were looking at BPL as a competitive broadband delivery technology to cable and ADSL. Although technically do-able, BPL never got beyond the trial stage in most U.S. markets. As an example, a local power company here in Western Massachusetts launched a successful trial, running broadband over power lines to wireless access points mounted on the same utility poles that carry the power wires. Customers, with proper user-names and passwords, could then access the final connection wirelessly.

Why didn't this Western Massachusetts power company roll it out? Power companies have made, what I believe to be, a business decision not to go into the consumer broadband market because they would have to build, market and maintain a system that would be in direct competition with mature systems the cable and telecom companies already have in place.

Instead of abandoning the technology though - the power companies may have figured out a way to use BPL to provide services that the cable and telecom companies cannot offer. Stacey's article mentions a few companies working with the utility providers - specifically Current Communications, Telkonet and BPL Global. These companies are developing products in response to the Energy Independence and Security Act of 2007 that requires both the federal and state governments to modernize the electric grid using Smart Grid systems. What's a Smart Grid system? Here's a quote from the Current Communications website:

Smart Grid combines advanced sensing technology, two-way high-speed communications, 24/7 monitoring and enterprise analysis software and related services to provide location-specific, real-time action-able data to all departments in a utility.

Does it work? Here's another quote from Stacey's article:

The head of corporate planning at Con Edison in New York once told me that BPL was a boon for the utility because it allowed the company to know when problems in the grid occurred, sometimes before they caused outages. Prior to BPL, the system’s only feedback came in the form of angry phone calls from customers.

More efficient power grid management and happier customers - perhaps BPL has found a niche.