Low-Energy Mobile

Hi there!

It's been a while, but we're back again to bring you hard-won advice on ultra-low power mobile designs.  To be future-proof, this is no longer an option, but a must.

Developing mobile devices is all about power consumption.  Very simply, your battery wants to last as long as it can.  This is true for a smartphone, hearing aid, wireless networks, or a solar powered remote monitor.  In terms of design, it changes everything: batteries, circuit components, energy harvesters, and software -- it all takes a lot more care to design.

Brush Technology is involved in each of these applications in ultra-low power design.  Let’s take a look at some of these application, and you can decide where your next mobile design fits into the picture.

But first, your regular light relief with fries.

Gadgets corner

• Here’s a guaranteed entry in our ongoing bendable/roll-up smartphone saga.
• Flying car (video): a whole new level of mobile and a different kind of power.
• Single-connector USB3 docking & charging

Techie corner

• Endian solution for C: Are numbers stored big-end or little-end first?  Most programmers have to byte-swap to deal with this.  But in C there should be no reason the compiler can’t do the hard work and make programs much more portable.  [... more on our blog].

µA/MHz is only the beginning

Picking a low-power microcontroller is way more than just selecting the lowest-current device.  Their press releases want you to focus on low µA/MHz (power vs speed) but that may be the least of your power worries in a mobile device.  Every man and his dog are now selling microcontrollers containing a low-power ARM core at around 150µA/Mhz.  But the packaging around that core makes all the difference.  Let’s look inside an Energy Micro EFM32 microcontroller to see what it takes for their EFM32TG110 to be ahead of the pack.  The keys are sleep mode and sensor power.

On a modern design you may have to sense a capacitive-touch keypad, sample ambient light level, listen to a serial port, monitor wireless communications and a swipe card.  If you have to wake up your CPU 1000 times a second to check all these sensors, your battery life is shot.  It’s the difference between a one-year non-rechargeable battery life and a 10-year life.  And that means the difference between having a user-replaceable battery or a never-replace battery – which comes down to a quality user experience.  And Steve Jobs has shown us that user experience is what sells products.

The answer is ultimate sleep and low energy peripherals [... continued on our blog]

Energy sources: MEMS energy harvesters

Mobile devices simply can’t be tethered to wall sockets.  That means a battery and possibly an energy harvester.

An energy harvester could be simply a traditional solar panel – cheap, easy and improving all the time.  But if your product is inside someone’s pocket or a building, it might have to be something more modern.

The main alternative to solar is harvesting movement energy (though supply is so limited it really feels more like scavenging). This cutting-edge MEMS piezo harvester can still only produce microwatts from a moving human.

There is some development on MEMS devices for harvesting thermal energy, but it is less accessible than vibration.

You'll almost certainly need a voltage booster to be able to use the power from your energy harvester, and you might want to check out these MicroPower step-up boosters from Advanced Linear Devices.

But all these energy harvesters cannot power even a low-energy microchip more than part time.  In other words, you need an ultra-low power circuit design.

Ear-Level Data Logger

How do hearing specialists prescribe the right hearing protection for you? Good question.  At Brush we now have a working prototype of a sound level data logger mounted in a hearing-aid case.  Like a hearing aid, it needs to do all its digital processing on the strength of a tiny zinc-air battery.  Having a working proof of concept is the easy part.  The next stage is to focus on making the battery to last, and it means a careful overhaul of both software and hardware.

Hivemind: low power monitoring via satellite

We’re excited to be able to talk about our new Hivemind product.  Besides being a beekeeper’s dream come true :-), it features the themes of this issue.  Ultimate mobility is obtained with satellite communications, and it is low-energy enough to run from a small solar panel that is built right into its case.

The great thing is that bees are fascinating creatures, and understanding their behaviour is both intriguing and valuable.  The issue Hivemind solves is the standard beekeeper line “I wish I were here a week ago”.  Hivemind tells you when your hive is full of honey, or when bad weather has slowed things down.  Getting the timing wrong on a yard visit can mean a lot of missed production and opportunity cost.

We haven’t released yet, but we’re well on the way to a release early next year.  If you’d like to know more, visit our Hivemind web page or download the brochure [PDF].

Industrial batteries: Know what to look for

You thought a battery was just a battery? Think again. You probably know that your laptop has a lithium ion battery for its good capacity/weight ratio.  But your average laptop or phone battery lithium ion battery will explode if overcharged.  And it might start a fire if it sits around gulping heat on an average Australian farm in summer.  If it drops below zero, its voltage will sag where the device might stop working.  They’re just not industrial-strength devices.

There are as many battery technologies as the chemists can dream up.  But a few have become leaders.  For decades, the lead-acid battery has been the industrial backstay.  It’s used in vehicles, uninterruptible power supplies, alarm diallers, and remote monitors.

But finally a lithium alternative has emerged that is robust enough for industry. It’s the Lithium Iron Phosphate (LiFePO4) battery.  It won’t blow up on you or create fires, it has much lower self-leakage than lead acid, can be far smaller, support higher currents, and can last a decade longer.

However, as with any lithium battery, it takes a clever monitoring circuit to prevent over-voltage, under-voltage, over-current, and fast charging.  And even though it is now several years old, obtaining data on these batteries is confusingly difficult.  Try figuring out how long they will last at elevated temperatures: almost impossible without testing it yourself.

But battery R&D is heavily resourced for use in electric vehicles.  We hope that in a few years this article will be superseded with something better.