Slashdot Mirror
Guide To Designing Low Power Handhelds
randomErr writes "iAppliance had a nifty article about designing handhelds. As the state-of-the-art in low-power CPUs races forward, the CPU becomes one of the most critical components in the design of a handheld. New CPUs such as Intel's XScale, Alchemy Semiconductor's Au1000, and Transmeta's Crusoe provide the ability to scale clock frequency and voltage dynamically. As power consumption varies linearly with clock speed and as the square of core voltage, you'll want to have hardware hooks to be able to adjust both clock speed and voltage as necessary, based on device performance."
Just to point out to anyone who doesn't know, AMD aquired Alchemy Semiconductor.
CPU power is not the issue when it comes to portable computing. The real holy grail will be in acceptable display technology. Whether that be some sort of expanding/folding display technology or a lasar retinal display, something significantly better than our current technology is needed to really make a significant jump in usability and functionality.
If you want low power than asynchronous is the way to go. Amulet processors use much lower power than synchronous processors. They are asynchronous so they will slow down when the voltage drops or you go somewhere hot. When they are not working they don't use any power. There is no messing about with software controled clock control, you just stick it into a branch on spot and it freezes. This is great for things like pagers or handhelds where you dont even need to power the clock nets while you are not doing anything. A large processors clock power consumption can be as high as 80%.
You might have seen it already but this is me powering an Amulet2 off a mouse wheel. They are very robust.
Mouse powered Chips, Open source Processors and Lego
Palm systems are curently on top. They may only be B&W, but they get great battery life and do what most users need. Once you start entering the realm of music, that can be scaled over to an MP3 player instead of a Palm device.
However, once you start deciding to run higher end applications, give the machines net connects, etc. everything gets more complicated. Full color, integrated (or even unintegrated) 802.11b, sound and so on all drain batteries at an increased rate. My keyboard for my palmtop drains when it's plugged in, which is, obviously, why it's not plugged in all the time.
Battery life and functionality are both the keys. Is there a potential way to implement a self charging feature? Maybe harness the kinetic energy of movement to assist in charging the device? Most people with handhelds carry them everywhere. It wouldn't work well with high drain / low charge devices, like the Ipaq, Jornada, etc. which have charges of under 10 hours (at best) but maybe a system like this could achieve a few days or a week in a low drain device like a Palm m100.
I have no idea. Just a decidedly random thought that I had. Later.
Or one that combines such a self-winding pendulum drive with some solar cells and some of those nifty materials that convert thermal energy to electricity?
Maybe even some antennae that can absorb all the abundant radio/microwave radiation that cell towers, wi-Fi, bluetooth, high-power transmission lines, the sun, etc. etc. are constantly pumping out? Tesla's wireless power dreams finally realized!
I think that vastly increased use of such passive reclamation systems is about the only way that tomorrows electronic devices can manage to simultaneously get smaller AND significantly more powerful.
When Thales was asked what was difficult, he said, "To know one's self." And what was easy, "To advise another."
There are some good reasons why devices still use alkaline batteries instead of rechargable:
:)
- It's cheaper. Making the user buy AAA cells is cheaper than an expensive built-in rechargable. Be angry if you want, but the same shoppers that gripe are the ones that will pick the AAA model because it's $10 cheaper.
- Charger required. more $$$, bigger packaging, more travelling weight, country-specific voltage, UL Listing, the works.
- Alkalines last longer (per charge) than rechargables. On a device may go weeks without seeing a charger, this counts.
- Rechargable cells die. What do you do with a PalmV that no longer charges well? LiIon cells only last a year or two before they start to degrade quickly.
I'm not saying that these are valid reasons to require disposable batteries, but these are factors that manufacturers look at in deciding which way to go.
I really like FastCPU for PalmOS. I run it on my Treo. Its great to be able to overclock slow apps from 33 MHz to 66 - it makes a helluva difference, and, it doesn't lock up all that often.
The other cool thing about it is that I can underclock things like notepad or "to-do list" so they use less battery power while running.