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### Topic: 7 Segment LED reverse voltage problem (Read 1 time)previous topic - next topic

#### Manu08

##### Sep 09, 2012, 06:47 pm
Hey guys I need someone's help. I'm new to this and may have the wrong concepts. I bought a 2 digit 7 segment led with common anode. I've done some research here and on YouTube and found that I can hook up the cathode pins to some digital output pins on the arduino and set them to low. Also I've found out that I have to put a current resistor between the cathodes and the digital pins. Also it is recommended to use the 3.3v on the a ;)node side. I'm planning of just using one led to get the basics straight. I'm currently using the arduino uno r1.
Well my question is the following: when I set the output pins to HIGH to turn off the led, wouldn't that cause a reverse voltage on the led?

Thanks, and sorry for my bad English.

#### runaway_pancake

#1
##### Sep 09, 2012, 07:06 pm
If the Arduino is running from 3V and the common anode is at 3V then there's no reverse bias condition.
If your Arduino is running 5V then have the "CA" at 5V, too.
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

#### Manu08

#2
##### Sep 09, 2012, 07:24 pm
So you are suggesting to hook up the common anode to 5V and when setting the OUTPUT pin to HIGH I won't have a reverse voltage?

#### runaway_pancake

#3
##### Sep 09, 2012, 09:53 pm
Correct.
It's a component with 5V at both electrodes.
A diode with the anode at +5 and the cathode at +5.
A diode with the anode at +5, the cathode connected to a resistor, and the other end of the resistor at +5.
What's the voltage across?  0V

(NB A resistor is required between each segment/LED and each output pin.  You could get by with one resistor in the "CA" line, but you'd have to make certain that only one segment would be on at a time.  Stay with a resistor for each until, for now.)
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

#### Manu08

#4
##### Sep 11, 2012, 04:20 am
Ok, thanks a lot. I've done that, but now my arduino just resets everynow and then. I gonna check if it is my computer or something else.

#### runaway_pancake

#5
##### Sep 12, 2012, 02:27 am
Code: [Select]

|
5V------A_K----220?----| output pin
|
"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!

#6
thanks

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