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I wish to power this GPS module, but its typical current usage is 55mA, and in the datasheet of a similar GPS, it says it can peak at 60mA during acquisition.

How can I safely power it with the 5V of an Arduino Uno?
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Connect it to +5v and GND. The 5v regulator should be able to supply the additional 60ma. According to the specs, it is the 3.3v regulator that is limited to 50ma.

edit: This is how the ethernet shield (w5100) gets it's power, and it uses about 140ma.
« Last Edit: December 04, 2012, 07:29:46 am by SurferTim » Logged

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Any such limitations on the 5V?

I also came across this over here:
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Unfortunately, I believe all the pins on the arduinos are only rated for 40mA. So while your power supply might be able to provide more, if you take it from the power pins you should not draw more than that.
How true is this?
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That is applicable to the I/O pins on the Atmel processor, not the power supply. Like I said before, the w5100 gets power from the +5v on the Arduino the same way, and it uses over 100ma.
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Very well. Thank you  smiley
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The limitation on the 5V current drain is a bit more complex.

Firstly if running off USB then the USB 5V supply is used directly and it will typically have a limit of 500mA (though
this depends on what is providing the power - some USB power blobs provide more for instance).  There is
a 500mA poly fuse on the Arduino board to protect the USB supply I think.

If the board is powered via either the barrel jack or the Vin pin then the on-board regulator comes into play
to provide 5V.  Its main limitation is thermal - if it dissipates too much power it will shutdown to protect itself.

The power dissipated in the regulator is the voltage drop across it times the current through it.  Thus for a 12V
input supply there will be 12V - 5V = 7V across the regulator.  If 100mA is drawn by the Arduino and the GPS in
total (roughly right), that means 0.1A x 7V = 0.7W is dissipated in the regulator - this will make it hot, will probably
 cope though.   Using a 7V input supply would reduce that to 0.1A x 2V = 0.2W which is no problem at all.

So in general the more current from the regulator, the lower an input voltage you want.

Alternative methods of powering are to provide an external regulator (either linear like the on-board one,
or switch-mode DC->DC converter) to provide 5V - heatsinking can then be used to deal with higher
currents (or the DC->DC converter option is less wasteful anyway, typically > 80% power efficiency).
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Quote
Alternative methods of powering are to provide an external regulator (either linear like the on-board one, or switch-mode DC->DC converter) to provide 5V - heatsinking can then be used to deal with higher
currents (or the DC->DC converter option is less wasteful anyway, typically > 80% power efficiency).
You mean 7v (not 5v) to the barrel jack, correct? Both the Uno and Mega spec sheets now warn about supplying 5v power directly to the 5v pin. It can cause damage.

From the Uno reference page:
Quote
Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.
http://arduino.cc/en/Main/ArduinoBoardUno
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I was considering using a different GPS due to availability issues for something similar to this instructable. Minus the accelerometer. Will the 5V be enough for the GPS and the SD card socket?

Considering that this unit should work continuously for 3-5 days. What kind of power supply should I look at?
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If you are powering the Arduino from the usb port, you should be fine. It is the 5v regulator on the Uno/Mega that causes the heat problem. They are linear type regulators, and generate heat to drop the voltage to 5v. The higher the input voltage to the barrel jack, the more heat must be dissipated by the regulator to drop it to 5v. The minimum recommended input voltage to the barrel jack is 7 volts, and that voltage would produce the least heat on the regulator.
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So, using a 7V input to the barrel jack, what kind of battery capacity is needed considering the unit needs to work for 3-5 (12-hr) days?
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Quote
You mean 7v (not 5v) to the barrel jack, correct? Both the Uno and Mega spec sheets now warn about supplying 5v power directly to the 5v pin. It can cause damage.

The barrel jack is on the Vin not the 5V pin. Its normally  9V to the barrel jack.

Mark
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So, using a 7V input to the barrel jack, what kind of battery capacity is needed considering the unit needs to work for 3-5 (12-hr) days?

Well that depends on the total current draw of your complete project. A basic arduino board consumes about 70Ma or so, your GPS says 55ma. So are there any other 'loads' consuming power such as LEDs and such used in the project? Once you know the total mA draw then you can calculate the battery duration time using the batteries mAH rating.

Lefty

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