Can LED 2 pins be used on port A1-A5?

NETMF & Gadgeteer
21

Could I use these LEDs with the proper resister? [url]http://www.frys.com/product/625972[/url]

Looks like I would need a 82ohm resister according http://www.ledcalc.com

I couldn’t find any LEDs that were specifically less than 4ma.

I’m a expert C# programmer, but a total amateur at electronics.

Your assistance is greatly appreciated.

-Eric

22

EricM,

that seems correct.

23

Do not use 80 oh resistors.

Use 220 or 330 ohm resistor with any small LED you have (3mm or less), even if it is more than 4mA.

If you want larger LEDs then you can use the ones we offer which have built in transistor…or build your own of course.

24

Maybe this is what killed my FEZ Domino?
Im used to the Arduino 40mA pins and was not aware of that the FEZ only could handle 1/10 of that current. The LEDs Im using are regular 5mm that draws about 20-30mA. So if I connected that to an IO pin and a 220R resistor to ground, I could fry my processor?

This is probably in the documentation but I have obviously missed it. Can you point out where to find it as there might be more issues I need to be aware of.

25

That is a possibility. I will forward this to the team so they can make sure this is documented clearly if it is not.

26

Here comes the benefit of LED component board on tinyclr.com.
A transistor is driving the BIG LED. 8)

27

I thought about this more. If you are using 220 ohm with 3.3V an the LED has 0.7V drop then you end up with 11mA. This is more than 4mA but I doubt this will cause any problems.

So, you can use any LED you like as long as the resistor is 470 ohm. Of course the LED may not come on if it is large but it will not damage your FEZ.

The way I like this, use small LEDs (20mA or less) with 330 ohm resistor and you will have about 8mA which should be just fine. Going slightly over 4mA will lower the voltage but should not damage the processor. With voltage going lower you will even have less than 8mA.

28

How about a schematic for the recommended LED usage. Including the transistor if that is what is recommended.

This conversation is really making me gun-shy about tinkering … I don’t want to fry my Domino like others have.

My problem with ones you sell is they are freaking huge and require a cable and one of the plug connectors. I just wanted something I could wire up on a bread board.

-Eric

29

Buy a Panda for initial interfacing experimentation? ;D

30

You can wire your (3mm or smaller) LED through breadboard without any worries. You need to add 470 ohm resistor in series

I found this online if this helps [url]http://www.intl-lighttech.com/applications/light-source-apps/discrete-leds/img/appl-leds_basicdc.jpg[/url]

31

I should have I guess, but I wanted the option of having USB host functionality.

-Eric

32

Sorry I lost track. We started with an old thread and started talking about LED and now USB!

Can we make new thread for each question so we are able to help you better?

Edit: oh I see, you are commenting on FEZ Panda not having USB host :slight_smile: Do not worry, your FEZ Domino will do the job just fine. If you are not sure, always come and ask and we will always be here to help

33

You guys are great … no worries. I’m still waiting for my Domino to arrive. Can’t wait!

-Eric