One question. To power the Arduino you can use 5v from your usb port or an adapter, which should be rated between 7v and 12v. A 5v adapter could work, but is not recommended.
I have some mobile phone chargers laying around, which give 5v and have a usb connection. Since these connect to the usb port of the arduino and not the normal adapter port, could I safely use them although they give less voltage than is recommanded if I used a normal adapter?
A 5v adapter could work, but is not recommended.
No a 5V external output would be fine (disconnect the USB powering linlk). Just connect it to the 5V line of the Arduino. If it is over 5V then connect to the Vin.
Hello Mike,
Thanks for your reply. But I'm afraid I dont understand your answer.
I want to power the arduino by an adapter, not with my pc.
But I do want to use the usb port, by connecting the arduino to an iphone charger. This one gives 5v, similar to my pc.
I did understand that if you power the arduino on the other socket, it needs to be >5 volts, otherwise the voltage might fluctuat. I want to use the arduino to temperature logging, so a stable voltage is necessary.
Would you recommend the iphone charger, or should I buy a 6+V adapter?
You should be able to power am arduino via a power-only "USB Charger" just fine (complete with standard USB cable.) In fact, it's probably safer than going directly to the +5V lines...
But I'm afraid I dont understand your answer.
YOU CAN USE AN EXTERNAL POWER SUPPLY THAT IS 5V IF YOU CONNECT IT TO THE PIN MARKED 5V (AND GROUND) ON THE ARDUINO.
This is NOT powering it from the USB connector it is a separate plug in the wall supply that gives you exactly 5V.
If you have a power supply that gives you more than 5V then connect it to the Vin connector.
Read this:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html
I have powered the Arduino from a device that plugs into the mains and supplies 5V power through a USB connector. This works fine. The device uses the USB connector just for 5V power, and does not supply USB data at all.
Any power supply that gives more than 5V must go to the Vin and Ground connections.
I want to power the arduino by an adapter, not with my pc.
But I do want to use the usb port, by connecting the arduino to an iphone charger. This one gives 5v, similar to my pc.I did understand that if you power the arduino on the other socket, it needs to be >5 volts, otherwise the voltage might fluctuat. I want to use the arduino to temperature logging, so a stable voltage is necessary.
Would you recommend the iphone charger, or should I buy a 6+V adapter?
Can I try and summarise this (and incidentally test my own understanding of the fine detail)?
A decent charger that pretends to be a usb connection should supply something quite close to 5v and is easily connected via the Arduino's usb socket.
Most such chargers (and I'd hope all of Apple's) will give close enough to 5v, and steadily enough, to satisfy Arduino operation.
However, if you are really picky about a/d accuracy, you could meter what its actually delivering to the board. A suitable place to do that is from the "5v" connection point (near the analog in connectors).
The point about accuracy is that the actual voltage on that "5v" line is the default 'full scale' on the analog inputs.
(For use with some sensors, and at some temperatures, you can get much better accuracy by setting the analog reference to 'Internal' whereby you get a (separately regulated) 1.1 volts as full scale. Confusingly it gives you 2.56v on the old Mega8 analogReference() - Arduino Reference )
If you want to supply your own 'trust me its pretty close to 5v', then you could connect it either to the '5v' connection or the usb socket -- they are directly connected together on the board. Your choice of which connection to use can be determined by whatever is most convenient for you to cable to - probably the usb!
The alternative is to supply a voltage that is higher and not necessarily as stable -- and let the on-board voltage regulator do its stuff.
Going that way, 7 to 12v would be better than the 6v that the poster mentions - so as to ensure a stable '5v' output.
To connect that sort of supply to the on-board regulator, it could be connected either to the 'power jack' next to usb socket, OR to the '9v' connection point alongside the analog-in block - whichever is most convenient for you.
Using the Arduino's regulator like that, you need to set the power jumper to "EXT". But if you use your own regulated '5v' supply, whether its connected to the usb or the '5v' input, set the jumper to 'USB'. Naturally, if you have a Duemilanove (2009 Arduino) that switching is automagic.
Thank you, that is very clear. I'll have a look at this internal reference, as it might sound as something usefull.
Can I assume that a computer supplies a very stable 5v from it's usb port?
Can I assume that a computer supplies a very stable 5v from it's usb port?
Well, left to itself, it should be fairly 'stable'.
However, if you are powering scanners, hard disks, etc, etc from the usb then you might expect some variations. And it will likely pick up RF noise.
But, if you are using it as a reference for measurements and you want maximum accuracy, you should NOT assume that it is spot on 5.000 volts.
You can meter the voltage that is being seen at the "5 volt" Arduino pin.
Its always a good idea to recognise your assumptions -- which enables you to test them for validity.
Rather than calibrating your power supply and temperature sensor independently, might it be most practical to just calibrate the entire system as a unit?
Thanks, that is of great help.
I was already planning to calibrate the temperature sensor together with the arduino and power supply, before use.
Before, you mentioned alternative reference voltage (AnalogReference). I haven't figured out how the 1.1V works, as I don't understand who should deliver it. Does it come from the Arduino, or externally (why is it then referred to as internal?)?
I did come up with another solution, which would take care of all the uncertainties (I think). If I would use the 3.3V output of the arduino and connect it to the AREF port and use it to feed the analog input, I should have a stable signal, shouldn't I?
My understanding (and I hope someone will correct me if I'm wrong) is that the best you can easily get is the 1.1v processor internal reference (and its dead easy to use - no wiring!) The 3.3v should be pretty good too - it comes from the FTDI (usb) chip.
You'd have to check the datasheets to establish the specifications for voltage tolerance; my belief is that both would be rather better than the ±10% that usb can deliver.
Regardless of the specification, your chips could be much better (but they shouldn't be any worse) than spec.
Tinker and see!