I want to decrease the power consumption of the Uno Rev. 3. Some questions:
It looks to me like the Microchip MCP1826S-5002E/DB voltage regulator would
be a significant upgrade, since it has quiescent current of 0.1 mA vs. the
6-10 mA of the NCP1117 that the Uno.R3 comes with. The devices have the
same footprint. Is there any reason not to just remove one and put the
other in its place? Then with the 328P asleep power use should be lower.
Are there any other devices on the board that suck a lot of power?
In particular I wonder about the ATMEGA16U2-MU that handles the serial
communication... is guy just always on? If so, what happens if you just
remove it and use ISP instead?
Why not use a Promini instead? Only 1 regulator, no USB/Serial chip, no Rx/Tx LEDs, can get it in 8 MHz/3.3V version.
Program with an FTDI Basic, or connect a Programmer to the VCC/GND/Reset/SCK/MISO/MOSI pins (ICSP).
Check the current draw on Micrel MIC5205 series of parts
Good catch. That is a problem given I was hoping to use batteries. I guess
there's no easy way to do this and maybe I need a timer and a step-down
converter with shutdown or something.
If you were under 6.5 V, it looks like PWRIN doesn't connect to anything
except the regulator though, so could do one of these things:
use a 7V external supply (assuming >0.5 V drop on the polarity protection
diode D1)
Remove the polarity protection diode D1 and use 6V supply
CrossRoads:
Why not use a Promini instead? Only 1 regulator, no USB/Serial chip, no Rx/Tx LEDs, can get it in 8 MHz/3.3V version.
Program with an FTDI Basic, or connect a Programmer to the VCC/GND/Reset/SCK/MISO/MOSI pins (ICSP).
I was hoping to use some Arduino form-factor shields
So batteries - power from AA battery pack into 5V pin, or use USB cable and power via USB connector.
3 alkaline good for 4.5V.
4 rechargeable (NiMH for example) good for 4.8V.
High capacity NiMH are available, like 2700mAH.
Longer runtime needed? C cells, D cells.
Yes, you could supply your Arduino directly from batteries (<6volt), connected to the 5volt line or with a hacked USB lead.
Downside is that the onboard regulator still draws idle current.
And the A/D converter has no 5volt reference anymore. Problems if you want to measure with that.
Powerwise, lineair regulators usually loose against switching regulators. Do the maths.
Switching regulators are more expensive, but usually the better solution for battery operation.
If you can solder SMD, replace the onboard lineair regulator with this switchmode regulator.
Now you can use a 2-Lipo pack (~7.4volt) or a 12volt lead-acid battery very efficiently.
Leo..
switching regulators are highly efficient at larger currents (90% - 95%).
whenever it comes to very low currents you will have a reverse effect. in that scenario their efficiency is close to a catastrophy. so you better use batteries and remove the onboard voltage regulator.
True, therefore if you use switching regulators, use small ones.
The one I linked to has a current/efficiency graph and an advertised no-load current of 0.2mA.
Onboard lineair regulators could be 4-10mA.
As always, measure and do the maths.
Leo..