On Wed, May 08, 2002 at 03:31:19PM -0700, John Waters wrote:
> Hi All,
>
> I've a circuit that consumes about 100mA during operation, it now uses a
> wallwart as the power source, I need to convert it to a handheld device that
> will run on batteries. As the microcontroller works on 5 V, I did an
> experiment using a 9V battery, but it soon drained out in less than an hour
> when the voltage dropped below 5V. Is my circuit comsuming too much power
> than is impossible to work with battery? If so, I get to modify it to reduce
> power consumption, but how low the current consumption should go before it
> is considered suitable to run on battery?

There are so many variables here that my head is swirling. Let's get a handle
on some things:

1) Do you have an idea of what is sucking down 100ma of current? LED? heaters?
You're going to have to put the circuit on a power diet. Give us an overview
of what it contains and why it consumes 100ma.

2) You said 9V battery to 5V. How are you converting 9V to 5V? Linear
regulator? Switch mode? Very important because linear regulators drop voltage
by wasting power. So if you're using one nearly 1/2 of your power is wasted.

3) 9V battery. Are you married to it. 9V batteries have the absolute worst
capacity among the common battery types. What size batteries can you afford
in terms of size and space?

4) How long does this puppie have to run? 1 hr is too short. 2 weeks? 10
years?

The game is all power consumption vs. power capacity. Decrease the former,
increase the latter, and use no linear regulators, and you'll increase the
amount of time that your project will run on batteries.

BAJ

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