I have made a board for Arduino that has an DS1307 and an L298P. The board looks that it is working correctly. I have an RGB LED at pins 31, 33, 35 and I try to make them HIGH but the volts that Arduino gives is 1.6 Volts. I do not know if there is any problem with the circuit I think there is one. The circuit is in general free on internet for the 2 of the chips also I saw the datasheet of the chips.

Between Arduino and the board I have an ethernet board.

I used an external power with 10A at 12 volts also the USB cable and the problem is the same. Also before I make this combined board I was using two separate boards one for DS1307 and one for the motor. The RGB LED was working correctly.

The circuit for the motor does not get power from the Arduino, it has an external power supply input so only the ethernet and the DS1307 need Arduino's power in order to work. I will give the schematics and a photo. If there is any solution please help me.

I admit at the schematic there is a mesh at the lines of the RGB but this happened in order to have straight lines at the board.

schematic 1/3

schematic 2/3

schematic 3/3



  • \$\begingroup\$ Hi Kyrpav, please note the following: It is customary to place a space after sentence punctuation and also to capitalize "I" when referring to yourself. I have edited your question accordingly. \$\endgroup\$
    – JYelton
    Oct 25, 2013 at 19:20

1 Answer 1


I can see something strange:

your LEDs are connected between the MCU pins and the GND, without any resistors in series. Thus the voltages at the pin will not exceed the Vf of your LED.

And this is a problem, because it's likely that you are overloading your MCU pins. You should patch your PCB and add a resistor in series with each LED.

By the way, on the schematics, there are resistors close to the LED, but it seems they are just connected between MCU pins and GND. Is it a mistake ?

  • \$\begingroup\$ there are 3 pull down resistors for 3 pushbuttons at pins 32,36,40.This is something different in the pcb.Also in order to light a led to arduino you do not need to add a resistor of course we need a resistor for the led tho but is this realy the problem(that i did not place a resistor? \$\endgroup\$
    – kyrpav
    Oct 25, 2013 at 13:48
  • \$\begingroup\$ When i use an rgb led on a different pin in without a resistor i lights brightly with 1.9 volts and probably 30. In the rbg led that you saw in the photo the volts are 1.6 and probable the mA are the problem. \$\endgroup\$
    – kyrpav
    Oct 25, 2013 at 14:04
  • \$\begingroup\$ In the Arduino Mega schematics, there is no pin with an integrated resistor in series. You may rely on the internal output resistance of the pin to limit the current. Are you sure that your power supply is at the right voltage. Can you measure it and make sure it is at the right voltage? \$\endgroup\$
    – Blup1980
    Oct 25, 2013 at 14:07
  • \$\begingroup\$ Something more i used the same rbg led(smd) at another pin without resistor and it works perfect.I use the usb cable now and also the power supply i used was 12v dc and 3 amps and i checked it with a fluke multimeter it seems to be fine. Could the problem be at a soldering? Case there is no pin that connects with another to have problem at the circuit \ \$\endgroup\$
    – kyrpav
    Oct 25, 2013 at 14:10
  • \$\begingroup\$ The basic premise of your answer is faulty. If the led is connected without a resistor then sure, the current maybe too much for the IO pin but it will light the LED. \$\endgroup\$
    – Andy aka
    Oct 25, 2013 at 15:49

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