Wall-wart power supply

I've asked the following question twice elsewhere on this forum & I haven't gotten a reply. I hope that I will get a reply this time.

I have a wall-wart that has an output of 12V DC @300 mA. I know that the input voltage to the Arduino is between 7V & 12V DC. I don't know what the current requirement is. Is 300mA not enough or too much or just right?

It is fine for power the arduino itself as that takes about 40mA. It limits you for powering things like motors with external transistors or servos.

I think that there are 2 sizes of DC plugs - 1/8" & 1/4". The outside diameter of the plug on the wall wart is .25 inches. That will fit the Arduino, won't it?

I was concerned that 300 mA would be too much current, but apparently it isn't.

Did you actually measure the output voltage ? Is it a simple tranformer or is it a switching supply ? Is the output regulated to not exceed 12V ? Are you making any assumptions about actual output voltage based on the marketing of the product as a 12V supply?
Have you confirmed that it is indeed 12V and not 14V ?

Macnerd: I was concerned that 300 mA would be too much current, but apparently it isn't.

Where voltage is regulated "things" only consume as much current as they need. It's quite fine to use a power supply capable of many thousands of milliamps of current with an Arduino.

If, by your circuit error, the Arduino tries to consume over ~1A of current it will temporarily open its onboard fuse so you do have some level of protection there.

Macnerd:
I think that there are 2 sizes of DC plugs - 1/8" & 1/4". The outside diameter of the plug on the wall wart is .25 inches. That will fit the Arduino, won’t it?

I was concerned that 300 mA would be too much current, but apparently it isn’t.

Yes, 1/4’ is OK, provided the hole in the middle is minimum 2.1mm, and most are 2.5mm.

The 300mA is current available, current is not force-fed. If Arduino wants 40mA, that is the current demand, and that is all it takes. For all that, messing around with a 300mA supply is probably something you will regret. You will be better off getting a proper 9v 1000mA supply and using the 12v for something else. Your Arduino will thank you for it by running cooler.

Is it a simple transformer or is it a switching supply ? It is a simple transformer. The label states that the output is 12V @ 300mA.

For all that, messing around with a 300mA supply is probably something you will regret. You will be better off getting a proper 9v 1000mA supply and using the 12v for something else. Where do I get a "proper" 9V 1,000mA supply?

If, by your circuit error, the Arduino tries to consume over ~1A of current it will temporarily open its onboard fuse so you do have some level of protection there. Is the fuse resettable?

Did you actually measure the output voltage ? Is it a simple transformer or is it a switching supply ? Is the output regulated to not exceed 12V ? Are you making any assumptions about actual output voltage based on the marketing of the product as a 12V supply? Have you confirmed that it is indeed 12V and not 14V ? It's a wall wart. It came from a fluorescent tube emergency lantern. The lantern doesn't work. I haven't measured the output voltage. I guess that I should get a digital multimeter & measure the voltage of the wall wart, before I spend money on an Arduino, shouldn't I? In a DC plug, which is the positive & which is the negative? Is the outside of the plug negative or positive? I'd rather use a wall wart than a battery.

I just retired in February & I want to take up electronics as a hobby.

Macnerd: For all that, messing around with a 300mA supply is probably something you will regret. You will be better off getting a proper 9v 1000mA supply and using the 12v for something else. Where do I get a "proper" 9V 1,000mA supply?

EBay

The fuse resets. I don't think any of the other questions are relevant

Macnerd: Is it a simple transformer or is it a switching supply ? It is a simple transformer. The label states that the output is 12V @ 300mA.

For all that, messing around with a 300mA supply is probably something you will regret. You will be better off getting a proper 9v 1000mA supply and using the 12v for something else. Where do I get a "proper" 9V 1,000mA supply?

The walwart you have is fine. I use a 12V 2A one myself. And a 9V 1500mah, sometimes. The Arduino's can work with 7V - 12V (max 6v - 20v) Less volts is better though since it produce less heat.

Most applications will only use as much A as it needs. So even if you have a 10A power supply, and your circuit only needs 40mah, it will only consume 40mah.

I'm thinking about getting the Mega2560 ADK & the Arduino website recommends getting a 1.5 A power supply because the Android draws 750mA, I think. Perhaps I should get a wall wart that outputs more than 300mA. I don't know if I will ever get a smartphone, but couldn't I use the USB host on the Mega2560 ADK for something other than an Android? The ADK version is literally only a few dollars more than the non-ADK version. Or am I better off getting the non-ADK version & get a Beaglebone Black if I want to be able to control USB devices? Eventually, I'd like to have both an Arduino & a Beaglebone Black, but an Arduino would probably be easier for me, as a newbie, to understand. What could I use the USB host for on the Mega2560 ADK other than connecting it to a smartphone?

Macnerd: I'm thinking about getting the Mega2560 ADK & the Arduino website recommends getting a 1.5 A power supply because the Android draws 750mA, I think. Perhaps I should get a wall wart that outputs more than 300mA. I don't know if I will ever get a smartphone, but couldn't I use the USB host on the Mega2560 ADK for something other than an Android? The ADK version is literally only a few dollars more than the non-ADK version. Or am I better off getting the non-ADK version & get a Beaglebone Black if I want to be able to control USB devices? Eventually, I'd like to have both an Arduino & a Beaglebone Black, but an Arduino would probably be easier for me, as a newbie, to understand. What could I use the USB host for on the Mega2560 ADK other than connecting it to a smartphone?

I don't know anything about Beaglebone but I wouldn't bother getting an ADK unless you can see a real reason for one. You can always get a USB host shield later. Mine is gathering dust. I got it to host a dumb phone but I have not succeeded. The USB host enables you to connect to a swag of USB devices - keyboard, controllers etc.. I suspect that connecting to an Android smartphone is a minor aspect, but I have never understood that side of it. In the meantime any Arduino can connect to any Android phone by bluetooth, which is painless and costs $7. This what most people do.

I got a $50 smartphone last year primarily to use with Arduino. I just log data, but others use them as controllers.

You can always get a USB host shield later. I had forgotten about that. So, I really don't need to get the ADK version. I can get the non-ADK version instead. I've seen the Mega2560 at Radio Shack.

In the meantime any Arduino can connect to any Android phone by bluetooth, which is painless and costs $7. This what most people do. Fascinating.