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common anode and common cathode differences in 7segment display Answered

what are the changes need to do when using common anode seven segment display instead of common cathode seven segment display. hint:use transistors?

7 Replies

iceng (author)2015-02-08

See the common Cathode .... and common Anode pin wiring to a standard BCD to 7 Segment 74LS47 IC or a 4511 IC ..... thanks to


Or this VID .... a common anode tied to +5v with each of 7 segmented LEDs are driven directly through a resistor by 7 micro processor pin programmed in machine language to be able to make the LED spinner .

BTW this vid is banned in some countries ?

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iceng (author)nethmi.amanda.33442015-02-08

I wonder if you realize the depth of machine code needed to run a timing program, while running a continuous display control of all 7 LED segments producing a rolling segment of different brightness ? Which cannot be done by a driver IC !

BTW that blinking period (8th_segment) is a monitor of power to an inductive element inside the black box.

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-max- (author)2015-02-08

w/ common anode, all the anodes of the 7 segments are connected together. Likewise, in the common cathode, all the cathodes are connected together.

Tham means with the com. anode type, the one anode pin will go up to the positive supply rail, while the common cathode type, the common cathode will go down to ground or -Vcc.

If you are driving the segments with a transistor, that affects whether the transistor is on the high side or on the low side. If the output is a push-pull output, (it almost always is in modern electronics like op amps, microcontrollers, buffers, etc) then use whichever is more convenient, as long as you note that high-side segments will be on when the digital output is low, and vice versa. So you may want to use a inverting buffer, or do it in software or something.

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hkerr (author)2015-02-08

Common anode is a common positive (the common pin should be supplied with power and others to ground). Common cathode is a common negative (the common pin should be grounded and the others powered). If it is common anode the LED's will require more power, using transistors. If using an arduino you could just connect each pin to an output (through a resistor).

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