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[on:]

Hi all,
I'm in the process of mapping out my power needs for a project. Here are all the components:
13 * Arduino Pro Minis (5V/16Mhz/ATmega328)
1 * bluetooth modem
1 * digital compass
77 * photocells (6/arduino) (http://www.sparkfun.com/commerce/product_info.php?products_id=9088)

Everything will run off 5V (what that is is still TBD, but certainly battery power). Modem draws ~30mA, compass ~5mA, and each arduino I'm estimating at 10mA (primarily to power the ATmega328). That's a total of ~165mA, which I could easily power with 4AA's (or step-up a couple AA's)...which is of course making me question my math here.

My question is what do each of the photocells add to the current draw, or do they it? I'm afraid I'm learning electrical engineering on the fly, and not sure how to plan for this.

Thanks in advance!

Cheers,
David

EDIT: the Arduino's will all be talking to each other via I2C, e.g. http://www.uchobby.com/index.php/2008/09/16/introduction-to-i2c
...I imagine that would also impact the current draw/arduino?

[Reply #1 on:]

and each arduino I'm estimating at 10mA (primarily to power the ATmega328)

That's too low, you could try and measure it but I would say allow at least 50mA per Arduino.

The other stuff is insignificant by comparison. The photo cell is 1K under light, you will need a series resistor with each one, say 10K so 11K in 5V gives you about half a mA, but that would be taken up by the 50mA arduino allowance.
When you have an estimate then add half as much again as a safety margin when rating your supply.

[Reply #2 on:]

Great! That did seem pretty low, but it's what I gathered from the docs on the ATmega328, I'll test my ATmega164 in the morn to see what it draws, tho.

Thanks again for your input.

Best,
David

[Reply #3 on:]

The current draw on my Arduino Pro Mini w/ATmega164 = 27mA...so clearly my original estimate was too low. I'm hoping the ATmega328 doesn't require that much more power.

Thanks again for your help.

David

[Reply #4 on:]

I'm hoping the ATmega328 doesn't require that much more power.

Sorry but don't get your hopes up it is not likely to draw less as there is more memory in it.

[Reply #5 on:]

I meant too much more power than I measured with the ATmega128

Thanks.