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Topic: powering the Arduino Uno with a 12V battery (Read 15782 times) previous topic - next topic

Daanii


I had not thought of how I am going to power the other devices (specifically the Xbee) but the plan I believe was to use the battery to power the arduino, and then the arduino to power the Xbee.


That won't work. The XBee Pro uses 215 mA when transmitting. You can't get that through the Arduino 3.3 Volt output pin. That pin provides a maximum of 50 mA.

Putting this all together, the point is you have a big battery. It can provide a lot of power. Even the bigger laptop batteries don't have 84 Watt hours of power, and they can power a laptop--WiFi and all--for several hours.

But you still want to be careful how you use that power. You have a 12 Volt source that will power a 5 Volt device and a 3.3 Volt device. You want to be careful how you do that. Otherwise you will, at best, waste most of your power as heat and, at worst, burn out your devices.

It sounds like you want to get the easiest and quickest solution. At a minimum, that means getting a 3.3 Volt source for your XBee Pro.

CTE_T

Can I power the Arduino with the 12v battery and just find another battery source for the Xbee? Perhaps 2 D-Batteries? I still need them to last more than an hour.

Daanii

#17
Feb 29, 2012, 08:56 pm Last Edit: Feb 29, 2012, 09:13 pm by Daanii Reason: 1
Two D cells would certainly give you enough power for several hours of operation. But connecting the XBee directly to the batteries will probably not give you stable operation. The specs for the XBee modules I looked at said they take from 2.8 Volts to 3.4 Volts. I'd put a low dropout voltage regulator in there to stabilize the power. Something like: ww1.microchip.com/downloads/en/DeviceDoc/21826b.pdf

UPDATE: I did the math wrong. If you wanted to use that Microchip voltage regulator, you would need three D cells.

CrossRoads

The Rev of the Uno will determine how much 3.3V current is available. The later revisions had a seperate 3.3V regulator which I'm pretty sure are more capable than the 50mA that the FT232 was capable of supplying. Have to check the schematic for your board and see what is used.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

CTE_T

Quote
Two D cells would certainly give you enough power for several hours of operation. But connecting the XBee directly to the batteries will probably not give you stable operation. The specs for the XBee modules I looked at said they take from 2.8 Volts to 3.4 Volts. I'd put a low dropout voltage regulator in there to stabilize the power. Something like: ww1.microchip.com/downloads/en/DeviceDoc/21826b.pdf

UPDATE: I did the math wrong. If you wanted to use that Microchip voltage regulator, you would need three D cells.


Quote
Only 1 hour - that should a snap.

Given where you are currently at, I would still try the ~16 ohm series-R in the power line from the 12V battery, as the
easiest fix.

OTOH, in pretty much all of my creations, I use rechargeable NiMH AA cells. [forget non-rechargeable]. This includes
most of my robots.

Current NiMH AA cells have energy store in the 2200-2500 mA-hr range, and should run even an XBee-Pro for about
20-hours at 50% transmission duty-cycle. Also, of course, you can choose the #of cells to wire in series to fit the
application. I use 5 or 6 cells in my robots that use R/C servos.

The same should be good for powering your Arduino board, and the v.reg shouldn't overheat. 6 cells might be
better than 5 cells, as individual cell voltage drops to about 1 volt when the energy is depleted, and 6*1V = 6V,
which is about the low end to keep the v.reg from dropping out.


I'd prefer not to have to order any extra parts or regulators or dividers or anything. We can get batteries easily, but I'm trying to make this as simple as possible.

Quote
The Rev of the Uno will determine how much 3.3V current is available. The later revisions had a seperate 3.3V regulator which I'm pretty sure are more capable than the 50mA that the FT232 was capable of supplying. Have to check the schematic for your board and see what is used.


What is the 'Rev' ? (reg. maybe?) And I do not have a Arduino Uno board or an Xbee Pro in my possession right now. We will order whatever the latest Arduino Uno is available (R3?) and the exact Pro model we are ordering I don't have the website link for on this computer, but I can post it tomorrow.

Can I use the 3.3v pin slot on the Uno to power the Xbee?

Daanii


The Rev of the Uno will determine how much 3.3V current is available. The later revisions had a seperate 3.3V regulator which I'm pretty sure are more capable than the 50mA that the FT232 was capable of supplying. Have to check the schematic for your board and see what is used.


CrossRoads is right. I didn't know that. It looks like the voltage regulator is an LP2985, with a "guaranteed" 150 mA output current. Should work fine for an XBee, but may not be enough for an XBee Pro.

You would also be pulling a lot of 12 Volt current through the Arduino if you power both the Arduino and the XBee Pro.

Daanii


Can I use the 3.3v pin slot on the Uno to power the Xbee?


It might work. It depends on how much transmitting you will be doing. An XBee module should be safe. An XBee Pro module probably takes too much current.

CrossRoads

Uno Rev 3
LP2985-33DBVR
http://search.digikey.com/us/en/products/LP2985-33DBVR/296-18476-1-ND/809911

This guy is good for 150mA. It gets its 5V source from the 5V regulator when powered externally.
If you need 215mA for an XBee Pro you need an external source.

Or maybe a board with regulator built into it:
http://www.sparkfun.com/products/9132
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Daanii

#23
Feb 29, 2012, 10:33 pm Last Edit: Feb 29, 2012, 10:35 pm by Daanii Reason: 1

Or maybe a board with regulator built into it:
http://www.sparkfun.com/products/9132


That board too can only put out up to 150 mA of 3.3 Volt power. Datasheet for its voltage regulator is here: http://www.micrel.com/_PDF/mic5205.pdf

Not enough to handle an XBee Pro when transmitting.

CTE_T

#24
Feb 29, 2012, 11:02 pm Last Edit: Feb 29, 2012, 11:43 pm by CTE_T Reason: 1
I don't think powering the Xbee from the Arduino board itself is an option now that I'm drawing things out. I will need the Vin and a ground pin for the 12v battery to power then I have a pot. that I need to connect to the 5v and other ground pin on the Uno and also to an Analog Input (not a problem). That leaves only the 3.3v pin left right? Assuming I'm wiring everything correctly.

EDIT:
I wrote Arduino where Xbee is now originally -.-"

CrossRoads

You will need all the grounds from your different devices connected. That connection can be made at one of the devices and then brought to an Arduino pin.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

CTE_T

More research, more changes in the design itself. The grounds need to be all hooked together, this makes sense, however I had to make a whole new thread about the pot because I am unsure of how it will affect my project, including the power design, not including I still need to figure how to power the Xbee Pro :/

CrossRoads

XBee pro, go with an external 3.3V regulator as suggested earlier:

http://search.digikey.com/us/en/products/OKI-78SR-3.3%2F1.5-W36-C/811-2195-5-ND/2259780

Pot can use a simple voltage divider to get down to 0-5V level for analog input:
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Brad Burleson


Not enough to handle an XBee Pro when transmitting.


Looks like actual power usage of an XBee Pro depends on the model being used.

For example, according to the XBee Pro Series 1 datasheet (http://www.sparkfun.com/datasheets/Wireless/Zigbee/XBee-Datasheet.pdf), the non RPSMA modules use 250mA when transmitting (and the "international versions" use under 200mA).

Seems that the Adafruit module (http://www.adafruit.com/products/126) may work as-is.

FWIW,

Brad.

CTE_T

Maybe this will help... Here are the components we are using:

Arduino Uno
+
http://www.trossenrobotics.com/store/p/6367-XBee-Shield-V1-1.aspx
+
http://search.digikey.com/us/en/products/XBP24BZ7PIT-004/602-1179-ND/2344899

This is why I am so confused. It seems like I just plug it all into the Arduino and the Arduino will power it?

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