Re: **LOW** Power applications


linnix wrote:
12 weeks is not a long time for battery power. If the sensor takes
little power and if it only has to be checked once in a while, almost
any CMOS microcontroller will do the trick. MSP430, PIC (preferably
the low power series) etc.

Or an AVR, 1.8V / 0.02 mA at 32KHz. 5V / 20 mA at 2MHz.

A typical approach would be to use a watch
crystal to clock the unit under most conditions, and perhaps a second
clock source such as a 4MHz crystal for serial communications when
it's time to upload the data.

If time is not absoulely critical, you can use the internal RC. Set it
to 32KHz regularly and boost it to 2MHz (for 19200 baud) for data dump.
You also need to switch off the RS232 drivers (eg. Max232), since it
draws 10mA all the time. You can log the start and end real time to
recalibate your data stream.

You can make it run from a lithium
button cell, AA batteries or whatever. Depending on the micro you may
need to provide BOR or other functions off-chip to get the current low
enough.

BOR/DOD included in most AVR. Triggered at 2.7V or 1.8V.

We are currently running an experiment with such:
Run at 2Mhz for 1/10 of a second, use A2D to check the battery voltage.
Talk to the PC. Drop to 32KHz for 9/10 of a second. We are using 2
1600mA C cells. It is day 2 of the test, with the max232 connected.
The next test will have the max232 power off as well. I will report
back on the results.

Good approach. Works the same way with PICs. Also, data may be stored
in internal (256 bytes) or external (mucho) eeprom and dumped later.
If logged events cause a digital data transistion, then there is also
Sleep mode - could run that way for years.

Luhan

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