7-Segment LED Not Working
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7-Segment LED Not Working

by DangerDog2000 on Mon Dec 03, 2012 8:27 pm

Hi-
I purchased the 7-segment LED with the 4-pin backpack and I'm unable to get them to light up.

I've followed all the directions on the site:
http://learn.adafruit.com/adafruit-led- ... t-backpack

Here's where I'm at:
1. The program compiles error free.
2. After uploading it to my arduino I check the serial monitor and it outputs "7 Segment Backpack Test" - So the program appears to be working and uploaded to my arduino. I hit reset and it pops out another "7 segment..." line. It works.
3. There are only 4 pins and I've wired them, re-wired them, again and again to make sure I did not do a silly mistake... nothing makes these things light up.
4. I've checked all my soldering, went back and touched up the soldering to make sure all is just dandy... still no lights.
I've attached a photo too!

Is there a simple way to de-bug this? Is there anything else I should be doing? What is the likelihood of a defective part?

And help would be great. Thanks!
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Re: 7-Segment LED Not Working

by adafruit on Mon Dec 03, 2012 9:12 pm

try connecting to Analog 4 and 5?


Connect CLK to the I2C clock - on Arduino UNO thats Analog #5, on the Leonardo its Digital #3, on the Mega its digital #21
Connect DAT to the I2C data - on Arduino UNO thats Analog #4, on the Leonardo its Digital #2, on the Mega its digital #20
Connect GND to common ground
Connect VCC+ to power - 5V is best but 3V also seems to work for 3V microcontrollers.
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Re: 7-Segment LED Not Working

by Garyedwards on Tue Dec 04, 2012 9:43 am

DangerDog2000 wrote:Hi-
I purchased the 7-segment LED with the 4-pin backpack and I'm unable to get them to light up.

I've followed all the directions on the site:


Here's where I'm at:
1. The program compiles error free.
2. After uploading it to my arduino I check the serial monitor and it outputs "7 Segment Backpack Test" - So the program appears to be working and uploaded to my arduino. I hit reset and it pops out another "7 segment..." line. It works.
3. There are only 4 pins and I've wired them, re-wired them, again and again to make sure I did not do a silly mistake... nothing makes these things light up.
4. I've checked all my soldering, went back and touched up the soldering to make sure all is just dandy... still no peimar led lights.
I've attached a photo too!

Is there a simple way to de-bug this? Is there anything else I should be doing? What is the likelihood of a defective part?


And help would be great. Thanks!


You need to check fuses are they working properly?
Last edited by Garyedwards on Wed Dec 05, 2012 12:55 am, edited 1 time in total.
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Re: 7-Segment LED Not Working

by DangerDog2000 on Tue Dec 04, 2012 2:30 pm

Thank you for the replies. The Arduino/board was purchased complete and has been working fine. I just tested a blinking LED program and it works.

I don't know how to check fuses. I looked online and read a few articles but they looked like they were for people building their own boards. Everything on the board seems to work... How could I test the fuses?

Here is how I have the pins wired:
1) +/VCC --> 5V on the board
2) -/GND --> GND on the board
3) D/SDA --> Pin 4
4) C/SCL --> Pin 5

The instructions say: "
Connect CLK to the I2C clock - on Arduino UNO thats Analog #5...
Connect DAT to the I2C data - on Arduino UNO thats Analog #4..."
A assume that it is referencing pins 0-13 and not the Analog In pins A0-A5.

I've tried both the 'Digital' row of pins as well as the 'Analog In' ... when I look up in my little manual the pins that support pulse width modulation are digital pins 3,5,6,9,10,11. I don't see pin 4 in there.

Thanks again for your help!
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Re: 7-Segment LED Not Working

by pburgess on Tue Dec 04, 2012 3:43 pm

Yes, you actually want Analog pins 4 and 5. These perform double-duty as the I2C bus interface.

Alternately, with an "R3" Uno (looks like you have one there), the two unlabeled pins just past AREF are SDA and SCL. Those'll work too.
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Re: 7-Segment LED Not Working

by DangerDog2000 on Tue Dec 04, 2012 4:37 pm

Got it! Thanks again for all your help.

Here's what my problem was:
When I had them on the wrong pins, I would leave the controller on and test other pins and nothing worked. I tried hitting RESET between each time and when I had the pins correct, whala... it's working!

Problem solved.
Have a great day!
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