On Mon, Mar 15, 2004 at 11:05:40PM -0500, Robert L Cochran wrote:
> What does the PIC nanowatt technology allow you to do, exactly? Wat are
> the advantages?

The primary advantage is that it gives you, the designer, the opportunity
to create ultra low power designs. With extended watchdog modes, multi
frequency clocks, and dynamic multiple clock selection. it is possible to
create systems that barely use more power than the battery sitting on the
shelf.

>
> Does it mean that a PIC with this technology only needs low input power?

Not exactly. If you run a nanowatt PIC at 20 Mhz and 5V, it'll draw exactly
the same amount of power as a non nanowatt part. However with the nanowatt
part it's possible to greatly slow the clock, which reduces the power
consumption greatly. The combination gives you a lot of flexibility: fast when
you need it, slow when you don't.

> If so, and even though this sounds stupid, how do I supply it? I'm
> wondering how to set up a power supply for a low-power PIC -- if this is
> true, I mean.

Not stupid in the least. In fact a lot of novices brag about using low power
parts with a battery. But further into the discussion you realize that they
are using a linear regulator that's sucking down almost half the battery's
power.

Some quick rules of thumb:

1) Switching regulators are the ticket for high efficiency. It's possible to
get 90 percent or more usable power out of a switching regulator whereas
linear regulators routinely burn more than half of the available power.

2) While 9V batteries are convenient from the voltage standpoint, in terms of
overall power capacity, they really really suck. A single D cell can have
upwards of 10 times the power capacity of a 9V battery.

3) Lower voltages mean less power consumed.

4) Same for slower clock. With CMOS components, power usage occurs at clock
switch times, so the less times you switch the clock, the less power consumed.

5) A hard one for non-battery folks to swallow: if you're not actively using
a device, the TURN IT OFF!!!

6) Pick lower powered stuff. If you need an LED get an ultra efficient one,
then lower its power input, then blink it. Each reduces the power consumed.

>
> Yes I am new to PICs and microcontrolling and the features of the newer
> PICs. And very much want to learn the how-to-do-it.

No problem. You have good instincts on the subject. Microchip recognizes that
designers will need to be provided with information on using nanowatt
effectively. They have a Tips and Tricks document on their site here:

http://www.microchip.com/download/lit/pline/picmicro/families/18fxx20/41200a.pdf

It gives a lot of useful information on how to utilize nanowatt in ultra low
power situations.

Hope this helps,

BAJ

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