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Running MiniWireless on batteries  XML
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bertwagner



Joined: 11/03/2015 05:17:17
Messages: 1
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I have a MiniWireless-W-915 (RFM69W 915Mhz) and am trying to figure out how to run it off of widely available batteries such as 2xAAA or CR2032. If I understand, the MiniWireless requires at least 3.3v of input in order to work. Is there any way to reduce the power requirements of this board so that it can run off 3v? Any help would be greatly appreciated, thanks.
empeka



Joined: 21/12/2014 05:56:01
Messages: 18
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miniwireless has mcp1703 voltage regulator, so as long as you powering circuit through VCC pin you'll be fine with anything from 2.7 to 16V.

That's the safe way.
But if you're trying to squeeze every µA, you may try to remove MCP1703 completely and power your board directly throug 3V3 pin.
as long as input voltage stays ~3V you should be fine. Running atmega outside it's specs is possible, but when the voltage drops below certain threshold (that varies greatly depending on many factors, including temperature) you'll start experiencing undebuggable issues (memory corruption, freezes etc).
And that's where BOD kicks in. Atmega328p has (configurable) brown out detection that shuts down MCU when input voltage is below 4.3, 2.7 or 1.8V.
I'm not sure which value miniwireless boards are shipped with.

Also, read this: http://forum.anarduino.com/posts/list/0/39.page
empeka



Joined: 21/12/2014 05:56:01
Messages: 18
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few more random thoughts:
- you can downclock atmega328p to 8MHz with fuses (thus reducing power consumption and minimal voltage required to run stable)
- you could design switchable booster circuit:
1.8V is enough to run this MCU at 8MHz, so you could feed it directly from near-end-of-life battery (especially if it will be in sleep state most of the time [I assume])
MCU could swith such booster to boost voltage up to 3V3 when it's really required (using sensors, radio transmissions)
- consider using 3.6V batteries
 
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