MKR Voltage resistor

Hi.

I’m a newbie bulding an IR emitter with an MKR wifi board. This board have an operative voltage of 3,3 V and by my calculations a resistor between 50 end 60 ohm is the ideal for my project. Can someone help to confirm this values? Technical Data Sheet of the IR Led in attatch. Thanks in advance to everyone.

017-0275.pdf (388 KB)

Are you going to drive a power LED directly from a (7mA absolute max) 3.3volt MCU pin?

Better use a 2-transistor constant current driver for that LED.
Leo..

The GPIO of the microcontroller installed in MKR wifi basically only allows currents up to 2mA.
When the port is in high current mode, it allows 7mA source and 10mA sink, but neither is enough for your using.
It is not possible to directily drive the IR LED high power at the port and you have to use a transistor.

The two transistor constant current sink is the best solution, however you can also use a Logic Level MOSFET and a resistor to drive the IR LED. Expect the Vf to be in the range of 1.2V.

Só, i test it connecting the positive led leg to GPIO 9 and and negative to ground, without any resistor.. After load a sketch to the board the. Ir signals are emitted correctly. Better put a resistor on this?

When current is passed through the port beyond the specified value in the datasheet, the in chip port driver will be damaged.
If left untouched, your board will eventually bricked... :confused:

petersain:
Só, i test it connecting the positive led leg to GPIO 9 and and negative to ground, without any resistor.. After load a sketch to the board the. Ir signals are emitted correctly.

Nothing like "newbie" persistence to do it wrong. :roll_eyes:

Note the table shown above is NOT absolute maximum ratings! The "max" means "maximum current able to source to guarantee V_OH". Very different characteristic. The MCU does not have AMR current per pin but only maximum total current per group of pins. And that is quite high, 45 mA IIRC. If the other pins are not loaded heavily it is unlikely any damage will happen - the drivers are probably so weak they are unable to damage themselves.

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