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."

Comments

Alchemy Semiconductor

[Neon Spiral Injector]

Just to point out to anyone who doesn't know, AMD aquired Alchemy Semiconductor.

Re:Rechargable packs

[restauff]

Some PDAs have already started moving towards this end. The Visor Edge and some of the other Handspring Visor products have rechargeable batteries built in. My Edge charges in the same cradle as it syncs in, making it quite convenient.

Low power - Asynchronous

[brejc8]

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.

Re:Low power - Asynchronous

[brejc8]

Well actualy I am working on a method of converting standard synchronous designs into asynchronous ones.
My method requires no skills and is a simple push button conversion and on a sample design (MIPS R3000 clone) gave 30% higher speed.

It simply takes an EDIF of your synchronous design and creates an asynchronous EDIF.

Re:Rechargable packs

[Dr. Ion]

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.

Re:Rechargable packs

[swf]

What is it with this world, people haven't even heard of rechargable batteries!

There are some good reasons why devices still use alkaline batteries instead of rechargable:

Are you saying that alkaline and rechargable batteries have a different form factor? They don't. There are rechargable versions of all the common sizes (AA, AAA, etc.)

- 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. :)

That doesn't mean the AAA cell has to be alkaline. You can use rechargable AAAs.

- Charger required. more $$$, bigger packaging, more travelling weight, country-specific voltage, UL Listing, the works.

I don't know about you but I've been using rechargable AAAs for my palm and I haven't had a problem with the packaging, and having a recharger means I can also recharge AAs so I don't have to buy a new pack every week.

- Alkalines last longer (per charge) than rechargables. On a device may go weeks without seeing a charger, this counts.

It barely matters. You can get two rechargable AAAs with 700mAh per charge each. I don't even know what the alkaline AAAs do nowadays because they don't want to show how crappy their batteries actually are against rechargables. On a palm this means that you have to change the batteries about a day earlier, big deal - you save money after the second charge!

- 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.

You buy another pair of rechargable AAAs. LiIon may only last a year, but NiMH AAAs last by the recharge (around 1000). How long do you think that would last you?

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.

AAA DOES NOT MEAN ALKALINE! Go to your local hardware store and buy some rechargable AAAs. They work, they save you money and help stop the flood of disposable batteries.