# Arduino current output [closed]

Simple question: I'm researching before buying. Can any of the Arduino products output current on a 4-20mA scale? I've seen them with Analog inputs but not outputs. And if they do not, are there add on cards/Shields/Modules that you can add to use that as a function?

Thanks a bunch!

## closed as unclear what you're asking by Milliways, MatsK, user31481, gre_gor, MazarykOct 18 '17 at 13:39

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

• What does "output current" mean? – Milliways Oct 17 '17 at 6:45
• When in doubt, add a MOSFET as a switch to power directly from supply to load, without involving Arduino – user31481 Oct 17 '17 at 7:45
• What are you actually trying to do? Did some device spec say it needs 4-20mA? – gre_gor Oct 17 '17 at 17:27

Assuming a GPIO pins outputs 5V, and you need 20 mA (0.02A), why not use a resistor of 250 ohm?

``````V = I * R <=>
5 = 0.02 * R <=>
R = 5 / 0.02 = 250 ohm
``````

For 4 mA you use a resistor of 5 = 0.004 * R <=> R = 5 / 0.004 = 1,250 ohm

If you want it from the same GPIO pin, you can use also a trick:

• Take a LED from a GPIO which you control by PWM
• Tie a photosensor against the LED and put tape around both the LED and the photosensor
• The photosensor will have a certain resistance (you can control it by the LED)
• Run your circuit needing a current from 4-20mA through that photosensor.

Can any of the Arduino products output current on a 4-20mA scale?

It can be done but with limitations so severe that it may not be a practical solution. Use external circuitry / dedicated chips, however, it is quite doable.