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Topic: Connecting a 7 segment display.... (Read 429 times) previous topic - next topic

Ufoguy

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. :)
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BulletMagnet83

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.

CrossRoads

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  www.crossroadsfencing.com/BobuinoRev17.
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