Not properly working digital pin

Hello everyone,

I got a problem with some LED's on my Arduino. The circuit has 4 LEDs (with 150 Ohm resistor) all of them are separately wired to 4 digital pins. 3 of the LEDs are working just fine but the 4th one is not working good. It is not shining bright enough. I measured the voltages of the output pins to gnd: on the 3 working leds I measured about 4.6V. On the not properly working led are just 2.5V. How is that possible? It is connected to a digital pin just like the other ones.

I am using an Arduino Nano. To the nano are not only the leds connected but also an SPI Display, an A/D-Converter, 9 LDR's (4 of them to the A/D-Converter, all of them are wired to a 5 kOhm resistor), and the 4 leds. I attached a picture of the circuit diagram. Is it possible that there is not enough current for the circuit or something like that? But I dont think so. I am using a 5V 2A power cord. 2A should be enough.

I checked in the Code if the pinMode is set to OUTPUT and it is. I switched out the Arduinos but the problem still occured.

The 3 working leds are connected to digital pin 2, 3 and 4. The not working one is connected to d12. Does this affect anything? I cant think of anything else that could be causing that.

The lower right device is SPI controlled? D12 is part of the SPI bus, when SPI is active it is an Input pin.
I don't think you can override that to use it as an output.

Ahh yes. Youre right. I'll probably use the last analog pin for the led instead. Thank you very much!

I'll probably use the last analog pin for the led instead.

Note that on a Nano A6 and A7 are analogue-in only.
Only A0-A5 can be used as digital I/O.