[SOLVED] related selection of Common Cathode or Common anode seven segment displayes

Hi to All,

I have two different type of Seven segement displays from market...

1) Common Cathode
2) Common Anode

I had did some search for selection of seven segment displays for design....i.e. when to use common Cathode and when to use common anode....in another word what are the advantages that one will get if one is using common cathode displays over common anode and vice versa....but could not able to get satasficatory answers....

I will be more than happy if somebody higlights this points.....also please share some of your experience on this...

Looking fowards for responce...

Thanking you in advance....

milind.a.kulkarni said:

Hi to All,
I have two different type of Seven segement displays from market...
1) Common Cathode
2) Common Anode
I had did some search for selection of seven segment displays for design....i.e. when to use common Cathode and when to use common anode....in another word what are the advantages that one will get if one is using common cathode displays over common anode and vice versa....but could not able to get satasficatory answers....
I will be more than happy if somebody higlights this points.....also please share some of your experience on this...
Looking fowards for responce...
Thanking you in advance....

Click to expand...

hello,
from my personl experience i am never gonna use common anode.. take dis way..
suppose you have a 3 volt battery and you wired a led, it will glow fine now add 1 more led to same battery both will glow fine but not brighter as the single one was, now add another one as you keep on adding 7 led's to a single source of supply there glow fade away.. same in case of common anode suppose you have to display 1 on it 2 leds will b glowing but dey are fine but what if you want to display 8?? it looks very odd when you have to keep on diplaying digits 1 willl glow brighter but 8 will look very dim..
now take another case when you have 7 batteries and 7 leds and you are wiring one led with one battery.. all eill glow fine or say brighter that the case of common cathode..
sorry i was in a hurry, hope you got my point.

Nice point tushki7 ......I like your thought....Looking foward to have some more simillar thoughts.....

Thanks

milind.a.kulkarni said:

I had did some search for selection of seven segment displays for design....i.e. when to use common Cathode and when to use common anode....in another word what are the advantages that one will get if one is using common cathode displays over common anode and vice versa....but could not able to get satasficatory answers....

Click to expand...

The choice between Common Cathode and Common Anode usually comes down to whether the LED driver, MCU pin, transistor, etc, can source or sink the required current to drive the LED.

If the LED driver can reliably source the current required, then a Common Cathode configuration is warranted.

However, if the LED driver must sink the current required, then a Common Anode configuration should be utilized.

The active signal level of the LED driver may also influence the choice, Common Cathode requires an Active High Signal and Common Anode requires an Active Low Signal.

MCUs not only have a per PIN current sinking or sourcing limit, but a device Vdd and Vss, current sinking and sourcing limit as well.

By carefully planning which pins will being sourcing current and which pins will being sinking current, the Maximum Limits of the device can be preserved.

When planning your design you may find it advantageous to sink current from a Common Anode LED, than source current to a Common Cathode LED.

BigDog

I think a common cathode are a better choice when muxing several displays using BJTs, since NPNs are preferable choice for MCU interfacing.