GPOs and LEDs

bacall213 · Post by **bacall213** » Sun Sep 11, 2005 8:54 am

Hey,
I was wondering about the GPOs. I opted to not get the LED indicator because I have a couple leds I bought for a another project along with mounts and all, and so I'd like to hook them up myself, but I'm a bit confused with that whole +5 and GND. I see the positive and negative terminals for 3 GPOs, but what is the 4th +5 and GND for? I notice that the LED Indicator bus plugs into that entire plug, so does that mean I need to be using the GND when hooking up my LEDs?

Also, anyone know the required resister to bring a 5v connection down to 3v? I've got those darn forulas to figure it out somewhere, but I figure it's a common question and someone might know off hand. If not, I'll just look it up evenually. A little clarification would be useful, thanks!

Thanks!
Brian

Tom · Post by **Tom** » Mon Sep 12, 2005 11:02 am

Hi Brian,

Thank you for posting on the forum.

The fourth connection isn't for anything at all, and the +5V and gnd is for anything you would like to do with it. We had the unit connected like this so a standard 5pin connector would fit on the header.

If you would like an explaination on how the GPOs work, you can refer to http://www.lcdforums.com/forums/viewtopic.php?t=2898

I'm not sure why you would want to bring the resistor down to 3V. If you were to make a voltage divider with the 240ohm current limitting resistor, you can put a 360ohm resistor in series with it, and it would be 3V across the 360ohm resistor. There are other was too like 3V regulater or somekind of voltage attenuator. It's up to you on how to lower the voltage though.

If you have anymore questions or concerns, please feel free to post them.

Best Regards,

bacall213 · Post by **bacall213** » Mon Sep 12, 2005 2:15 pm

Hey, thanks for your help. I actually need to bring the voltage down to 3v from 5v because the LEDs I happen to have lying around are 3v to my knowledge. Thanks for your help, I'll see what I can do.

Brian

Tom · Post by **Tom** » Mon Sep 12, 2005 3:20 pm

Brian,

You won't need to lower the voltage to 3V, if you are using a LED. Since we put the resistor in series with the GPO, 3V will be dropped across the LED and 2V will be dropped across the current limiting resistor.

Best Regards,