maximum input current on Uno

Hi,

what is maximum input voltage for Uno board?
I have 5V 1A external input

is this possible to use Uno if connect my 3.3V device to Uno by USB cable?
If no, can I use both USB and external input?

Thank you

Your question makes absolutely no sense. I suspect you are misusing words, making your "question" unclear.

The title asks about maximum input current, then in the post you ask about maximum input voltage. Voltage and current are different things.

richardsunisa:
I have 5V 1A external input

I don't understand what a "external input" is? Aren't inputs external, by definition? I think you are misusing the word "input", which has a very specific meaning.

richardsunisa:
is this possible to use Uno if connect my 3.3V device to Uno by USB cable?

This I can't decipher at all.

richardsunisa:
If no, can I use both USB and external input?

Maybe you mean an external power supply?

Sorry for my english
I should rename this topic to input power for Uno

I mean we can power Arduino by USB cable and DC input

I see the DC input power for Uno is from 7 to 12V. Operation voltage is 5V. But it doesnt talk about input current
I have a 5V 1A DC power supply. Is this enough to supply Uno?

secondly, voltage to supply arduino via USB is 5V. So you can connect your device (e.g laptop, PC) with Arduino by USB
But my device has 3.3V USB connector. Is this enough to supply Uno?

richardsunisa:
I see the DC input power for Uno is from 7 to 12V. Operation voltage is 5V. But it doesnt talk about input current
I have a 5V 1A DC power supply. Is this enough to supply Uno?

Yes. The Uno itself takes about 50mA.

richardsunisa:
secondly, voltage to supply arduino via USB is 5V. So you can connect your device (e.g laptop, PC) with Arduino by USB
But my device has 3.3V USB connector. Is this enough to supply Uno?

I've never heard of a "3.3V USB connector". What device is it? The standard signal voltage for USB is 3.3V, but the standard power voltage is 5V.

I see many document talk about from 50 mA to 700 mA.
But I am not sure 1A is too high or damage my board

I am making a communication between Arduino and PX4 autopilot via UART
the idea is
PX4 UART <--> TTL to USB <--> Arduino

PX4 UART is 3.3V. there is the PX4 home page https://pixhawk.ethz.ch/px4/modules/px4io

Current rating of a source is the maximum it can supply.

Devices only draw what they need.

The Arduino board, by itself, draws 50mA.

If using a 5V supply, you must connect to the 5V pin AND NOT have it connected at the same time as USB.

richardsunisa:
I am making a communication between Arduino and PX4 autopilot via UART
the idea is
PX4 UART <--> TTL to USB <--> Arduino

PX4 UART is 3.3V. there is the PX4 home page https://pixhawk.ethz.ch/px4/modules/px4io

Why are you involving USB at all? You should be able to connect the PX4 UART direct to the Tx and Rx pins of a 3.3V Arduino, or via level shifters to the Tx and Rx pins of 5V Arduino. You just need to allow for the fact that if it is an Arduino with a built-in serial to USB converter, then the Rx pin is connected via 1K to the converter output, and your uart or level shifter needs to be strong enough to override that.

Thank you dc42,
I havent though abt it yet
That is the better way for this communication
How about this connection

UART Arduino
Ground Ground
CTS
TX RX
Rx Tx
5V Vin

And I dont need to use DC power?

That looks basically OK except for the following:

  1. To power an Arduino, you don't apply 5V to Vin. You either apply 5V to the +5V pin, or at least 6V to Vin, or at least 7V to the barrel jack.

  2. You can't connect the Rx pin of your 3.3V device direct to the Tx pin of a 5V Arduino, because 5V is too much for the 3.3V device. You need a voltage divider to reduce the 5V Tx output to a little less than 3.3V for the Rx pin. For example, connect a 10K resistor between Arduino Tx and device Rx, and an 18K resistor between device Rx and ground.

  3. Since the Arduino Uno has a 1k resistor between its Rx pin and the output of the usb-to-serial converter, to prevent this feeding 5V into the device Tx pin I suggest you add a 1.8K resistor between the device Tx pin and ground.