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Topic: How to power the board directly (Read 969 times) previous topic - next topic

marsy

Hi all,

I want to power my arduino uno without an adapter or battery. I am trying to connect to a host device that has a +12V out pin (which should be VERY consistent). Can I take that and plug it into the Vin port on the arduino? I also want to hook up a ps2 controller and I understand it needs +5V ( I do not need the motor so I don't need the 7.5); Can I just plug that into the 5V near the Vin port? Essentially this is going to be acting as a ps2 controller adapter for the host device.

CrossRoads

Yes & Yes.
Using Vin byasses the reverse polarity protection diode;  be sure to connect it correctly.
5V pin can supply 500-600mA of current. Regulator may get quite warm running from 12V.  You may need to provide some cooling openings in any enclosure you use.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

AlxDroidDev

#2
Oct 25, 2012, 05:15 pm Last Edit: Oct 25, 2012, 05:18 pm by AlxDroidDev Reason: 1
In theory you can do that, but...

... check what is the current requirement for the controller, because the 5V regulator in the arduino (NCP1117, datasheet here) can provide only up to 1A. Consider the arduino itself can use up to 350mA, so that leaves only 650mA for the controller and anything else you have connected to the arduino.

12V of power input is the upper limit recommended for the onboard voltage regulator. If you feed it with 12V, it's good to check how hot it is getting from time to time, because it does have to dissipate all that power somehow.

If the controller has a current requirement higher than 650mA, my suggestion is to have a LM7805 (up to 1A) or  LM317 (up to 1.5A) feed it instead, and use the 12V supply you have power the input of the LM7805/LM317 regulator.

Also make sure GND is common for everything: Arduino, 12V source, 7805/LM317 and PS2 controller.

Learn to live: Live to learn.
Showing off my work: http://arduino.cc/forum/index.php/topic,126197.0.html

marsy

Thanks for the fast replies! I've read about using a zener diode to siphon off extra voltage from the 12V. Would it be wise to do that so it doesn't get so hot?

Also, I am pretty new to electronics, this is going to be my first project, so I don't know what you mean by make sure I have a common ground? The host device supplies a ground pin, do you mean I should plug that in next to the Vin pin and plug the ps2 controller ground into the GND near the 5V pin?

AlxDroidDev


Also, I am pretty new to electronics, this is going to be my first project, so I don't know what you mean by make sure I have a common ground? The host device supplies a ground pin, do you mean I should plug that in next to the Vin pin and plug the ps2 controller ground into the GND near the 5V pin?


Yes. All the GND nets should be connected at some point.

You should be fine with the 12V supply, since the NCP1117 can accept up to 20V input. It is wise, however, to allow for proper ventilation of the regulator. The more current it has to supply, the more cooling it needs.

Learn to live: Live to learn.
Showing off my work: http://arduino.cc/forum/index.php/topic,126197.0.html

marsy

OK, so just to make sure, the following diagram shows exactly what I plan to plug in and where. This setup is 'safe' then I take it?



Thank you so much everyone, this is really helpful information to know!

AlxDroidDev

Yes, that is OK!

But like I said, make absolutely sure you check the current requirement of the controller that will be plugged to the 5V pin. If you don't check and it is too high, you'll fry the voltage regulator in the arduino.
Learn to live: Live to learn.
Showing off my work: http://arduino.cc/forum/index.php/topic,126197.0.html

marsy


CrossRoads

Not so fast - what do you mean by "SPI connection" on the analog pins?
SPI has a specific meaning, and the '328P has specific pins to drive signals:
D13 SCK
D12 MISO
D11 MOSI
D10 tyically used as Chip Select/Slave Select. Other pins can be used; D10 must be set as an output to enable Master SPI operation.

A4/A5 are I2C pins (I think A4 is SDA and A5 is SCK,  I might have those swapped).
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

marsy

The library I am using (PS2X) does SPI in the memory so it can be mapped to any pin and not just the PWM ones.

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