Pages: [1]   Go Down
Author Topic: Connecting a 7 segment display....  (Read 383 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Full Member
Karma: 2
Posts: 181
So, you want to make something, huh?
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I recently bought two 7 segment numeric displays. But it turns out that they have common positive instead of positive negative. I am unable to figure out how to drive them with an arduino. Can any one help me out?

And by the way what is cathode and what is anode? Positive or negative??

Thanks in advance. smiley

If you want to meet a beautiful nurse you must be patient.

South England
Offline Offline
Full Member
Karma: 3
Posts: 205
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Positive = Anode, Negative = Cathode.

And if it was me, I'd use the CAT4016 chip to drive common anode ones. If you want to drive them directly from the arduino there's no reason you can't (as long as you follow a few simple rules so you don't burn out your I/O pins). Try googling for "7 segment common anode arduino" and see what it throws up.

Global Moderator
Boston area, metrowest
Online Online
Brattain Member
Karma: 518
Posts: 26344
Author of "Arduino for Teens". Available for Design & Build services. Now with Unlimited Eagle board sizes!
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Another option is to use a couple TPIC6B595 shift registers to pull the cathodes low. High current, can handle 160mA from 8 LEDs on at once.
Available in DIP package, easy to breadboard with.
If you decide to make a big display, say 3 LEDs in series with 12V source for each segment, can drive that too.
Or just connect the 14 cathodes to 14 output pins (you have 20) with appropriate current limit resistor on each pin:
(5V - Vf)/.02A = Resistor
Vf usually ~2V, so (5V-2V)/.02A =  150 ohm.
Confirm the voltage drop across the LEDS you plan to use.

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at
Arduino for Teens available at

Pages: [1]   Go Up
Jump to: