Monday, 4 August 2014

arduino - Segment display – Why selecting segment by GND


I bought display and for my surprise it works same as display i already had. I must chose segment i want to light up by GND and not by output pin on my Arduino.


Is it normal or there is something what have to be done when working with this kind of displays?



For completeness, here is data sheet (SD-36)


Image 1 Image 2



Answer



This is quite normal. Segment displays like that are usually available in both common anode and common cathode types. What you originally had was a common cathode type. What you have now is a common anode type.


Segment display


Common anode displays are sometimes preferred because you can easily drive them with a darlington driver array, like the ULN2803:


ULN2803 driving common anode LEDs


The ULN2803 can sink quite a lot more current than a microcontroller GPIO pin, and so drive large, high brightness displays.


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