Asked — Edited


Hey guys,

I tried to use the original LED that comes with the WALL-E U-Command with the EZ-B, but the LED does not turn on (using digital ports).

Should the original LED work, or should I use another type of LED with the EZ-B?


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Must be connected backwards. LEDs are polarity specific: LED Info


Thanks for the quick reply DJ :)

Tried LED both ways (polarity), but still not turning on. Maybe I have 2 faulty LEDs...?

They were working before pulling apart the WALL-E though.


Connect one side to GND and the other to a SIGNAL pin of the EZ-B?


Yes, that's what I did.

Did you use the original LED for the eye on WALL-E?


I can't remember. I probably would have. I usually do use the LED's that come with the toys


Hey Hexxen,

Sometimes LEDs cannot self limit the current going through them and burn out when direct voltage is applied. Usually a 330 ohm or 220ohm resistor is needed to limit the current going through the LED to around 20mA for common 5mm LEDs.

EZ-B puts out 5V (TRUE) on each I/O pin, so using ohm's law Voltage = I(current) * Resistance 5V = 20mA * R

R = 5V/20mA = 250 ohms so the closest more common resistor values are 220 and 330 ohms. 330ohms is the safer value cause it limits the current going through the LED to 15mA. This resistor can be in series with the LED on either the anode (+) or cathode (-) of the LED.

Hope the mini-tutorial is useful:)


I never use a resistor with the EZ-B because digital I/O on the EZ-B has a source supply of 25mA only. All of my robots are just LED's connected directly to Signal and GND.

*Note: If you were to use Signal and +5, then you will need a resistor. And your LED would always be on.


Thanks for your help guys.

It turned out to be both original LEDs were faulty (I must have blown them somehow).

Tested a LED I pulled from a LED torch & it works fine with the EZ-B.

Now that I need to get some new blue LEDs for WALL-E, was thinking of using "color changing LEDs" instead to simulate Wall-e's different moods.

Will the color changing LEDs work with the EZ-B?


I have no experience with a color changing led, sorry. Let us know what you find though:) ... I usually use BlinkM's

You can easily blow an LED if you connect the power directly to +5 and GND without a resistor (even for a brief second while testing polarity). You do not need a resistor if you connect the LED directly to the EZ-B's DIGITAL I/O


I didn't know what a BlinkM did till you mentioning it now blush

That's exactly what I need so I'm getting one straight away instead of using the color changing LED.

The BlinkM has PWR - + & I2C d c pins, how do I connect the 2 d c pins to the EZ-B?


Answering my own question here.

Just looked at the EZ-B manual & it mentions the I2C header onboard :)


I have used RGB color changing LEDs with the EZ-B and had no problems. I`ve connected them to gnd and digital out pin.

United Kingdom

DJ, you should add the info about not requiring resistors if hooking up the LEDs to the signal wire on to the LEDs page of the hardware compatibility tutorial section.


I have RGB leds hooked up to the EZ-b I/o ports, no resistors. They work just fine. The only thing I've noticed is that when changing the intensity of a led or animating for instance a light pulse, that the leds will flicker excessivly every so often when the intensity is changed. Would using a resistor reduce this flickering?


@steveBurkett you don't need a resistor if the LED is connected to the I/O for its +5. The chip has internal resistors on the i/o:) .. However, you can't power anything more than LED's with the chip's I/O


Only potential issue I see is many if not most 5mm LEDs are not 5v. Most blue are 3.0- 3.7 v max as well as white , green, uv . Red is 2v so maybe the 5v smoked the led.


@ jstarne1

Hi, do you also experience flickering when changing the intensity of leds that are directly hooked up on the i/o ports?


If you are noticing flinkering while using PWM - you can probably fix that with a cemaric capacitor. It because there is practically no resistance in an LED, you could be visually seeing noise


cool! Thanks, ill give that a try. You guys are up late and must be drinking lots of coffee, I hope work is going well.