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Topic: Maximum Current/Voltage into an analog pin on an Arduino Uno (Read 34192 times) previous topic - next topic

Sonia

What is the maximum voltage and current that I can input into an analog pin on an Arduino Uno? The Uno website says:
- Input Voltage (recommended): 7-12V
- DC Current per I/O Pin: 40 mA

Is this correct?

Thanks
Natasha

RuggedCircuits

7-12V is the maximum input voltage you can apply to the external DC input power jack.

The analog input pin voltage is limited to 0V-5V. Anything outside that range will damage your microcontroller.

And to clarify, you do not "input" current into a pin. The pin decides how much current to draw in response to an applied voltage. If your applied voltage is in the range 0V-5V then the amount of current that will flow into the pin is very close to 0. Just make sure you configure the analog pin as an input, and not an output.

--
The Rugged Motor Driver: two H-bridges, more power than an L298, fully protected

CrossRoads

If you are using the pin as an output , make sure to use an appropriate current limit resistor to avoid sinking more than 40mA (absolue maximum) when driving an output low, or sourcing more than 40mA when driving an output high.
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.

Sonia

#3
Feb 12, 2011, 06:42 am Last Edit: Feb 12, 2011, 07:00 am by Sonia Reason: 1
Thanks for the clarification guys! I just have one more question, when defining the analog pins as input in the pinMode function, am i referring the the analog pins as A0, A1.... ie:

pinMode(A1, INPUT)

thanks

Grumpy_Mike

If you are only using the analogue inputs as analogue inputs then simple don't do anything it gets set automatically. If you are using them as a digital input or output then use pin number 14 for A0, 15 for A1 and so on.

The 5V input limit only applies to an arduino that is powered from 5V, lower voltage arduinos like those that run from 3.3v then that is the limit. This applies to not only analogue pins but also to digital pins.

Sonia


1oldfox

Hello all,
One more clarification please. I am building a 10 step resistive divider across the Uno 5v and gnd. Is it safe to apply the "5v" end of the string directly to the analog pin for a 'analogRead()'? If not, what size resistor would be suggested for a limiting resistor (resistor # 11)? The Uno is powered by the USB input.

TIA,

"If it ain't broke, fix it 'til it is". (unknown)
If it ain't broke, fix it 'til it is!

MorganS

Yes, for a 5V Arduino such as an Uno, 5V applied to any pin is safe.
GoForSmoke: "What GShield? You never mentioned a shield."

1oldfox

Thanks Morgan. Now I don't have to worry about filling the shop with smoke. :smiley-mr-green:
If it ain't broke, fix it 'til it is!

Wawa

If you have to measure "something" that is 5volt, use a resistor between that source and the input pin (4k7).
Just in case the Arduino is off, and the other device is on.
That limits fault current to 1mA.
Not needed ofcourse if the 5volt comes from the Arduino itself.
Leo..

Hardhack

Great question. I'm adding an Mega to a project that monitors the state of 18 TTL 5V logic ports and note a current draw when the Mega is off.  I've been considering adding currently limiting resistor would this be advisable when connecting an Arduino to a Logic circuit even if it is 5V powered?

Grumpy_Mike

You should not connect any input voltage to an un-powered anything. It causes parasitic powering and can lead to latch up. It is a great way to destroy electronics. A series resistor while cutting down the current does not change much. The real solution, apart from don't do it, is to use transistors to interface into your system.

Paul__B

Great question. I'm adding an Mega to a project that monitors the state of 18 TTL 5V logic ports and note a current draw when the Mega is off.
So - don't turn it off!  That should be a "given".

(Use 47k series resistors for monitoring logic circuits.)

raschemmel

Quote
Great question. I'm adding an Mega to a project that monitors the state of 18 TTL 5V logic ports and note a current draw when the Mega is off.
You can't have anything connected to the analog pins if you are going to turn it off. It will backfeed and power the entire mega through the analog pin because the Mega is off. I already tested this with an Uno.

If you have to power off the mega you need a relay to disconnect any analog inputs.

FYI, when the Mega is ON, the analog inputs draw 1.6 nA. If you turn the Mega OFF , it will draw whatever necessary to power the entire mega. In short, as stated. DON'T TURN IT OFF.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

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