8X8 LED Matrix Common Cathode


#1

Hi
I really believe I’ve searched properly this time. I also tried to create this myself, but it’s beyond my current skill levels.
Has anyone got an 8X8 common cathode LED Matrix part ? The datasheet for the one I have is at https://cdn-shop.adafruit.com/datasheets/1818_KWM-R30881XUAB.pdf
When I searched on “matrix”, all the parts I find seem to be 5X7 or common anode only.
Thanks,
Ben


#2

Try typing lbt2088ah in to the parts search bar (the magnifying glass icon on the parts bin) and hit enter.
Your search term wasn’t wide enough, led display will pull it up (along with a handful of others).

Peter


#3

That is a 60mm unit and the one they linked to is much smaller so if they need it to make a PCB it would not work.


#4

Thanks both for reply.
Just one question - should I have known to type “LBT2088AH” into the parts search ? I’m not sure where I would have got that code from ?


#5

I searched 8x8 and found it the first try. I also searched matrix and found it.


#6

If you searched “matrix” then it’s one of the ones I’ve already looked at as that’s the exact search I did too. I’ll check when I get home as to why I didn’t use that one - there’ll be a reason but I’ll need to be in front of Fritzing to remember why it was.


#7

The one you linked to has an outer dimension of 31.7mm and the matrix on it is 28mm x 28mm. The one in Fritzing core is marked as 60.5mm so it is very unlikely to work if you are making a pcb. If you are doing a drawing using the breadboard view then it should be fine.


#8

Well it’s definitely the breadboard and schematic that I am interested in rather than the PCB view so it should be OK. I’m just really intrigued to see why I thought I couldn’t use this one so I’ll report back later.
Thank you @sublimeartistry and @vanepp for the responses - it must be quite frustrating to be helping a total noob through things like this


#9

No, that is only needed to bring up only that particular unit and no others. As noted I used “led display” when 88 matrix didn’t work (I didn’t think to try 8x8) but then I knew there was an 88 matrix available in core parts too. Search is a bit odd (and usually over broad) so you need to try different keywords. Or you can use google “fritzing part 8*8 matrix led display” brings up other alternatives (although not the one in core interestingly).

Peter


#10

@vanepp - I just worked out why I didn’t pick the lbt2088ah when it came up in my search. There was no mention of common cathode or anode and the common anode ones seem to be the more popular choice when you look at what’s available out there. So I assumed this was a common anode one.
What is the best way to tell this for certain if the inspector does not show the type explicitly ?


#11

It wouldn’t matter for breadboard view.

If you drag the part out on to the schematic you will see the diodes are facing common cathode.


#12

Hmmmm - did notice two problems though - first, it’s bigger than some houses I’ve lived in and second, all the pins are the opposite way round and it’s non-flappable.
Maybe I should gird my loins and make one :thinking:


#13

Yes as I said twice before it is larger than the one you wanted. Also what do you mean by the pins are the wrong way around? Did you try rotating the part? In schematic you can also flip it side to side. If it is just the pin numbering then you can right click on it and open it in the parts editor and change the pin names that appear when you mouse over the pins.


#14

@sublimeartistry
Of course - I forgot I could just relabel the parts.
What I meant by the “opposite way round” is that the ones in the Fritzing part are like this …
1 16
2 15
3 14
4 13
5 12
6 11
7 10
8 9
… whereas the ones on mine are like …
16 1
15 2
14 3
13 4
12 5
11 6
10 7
9 8
The reason I think this is that I did a multimeter test on all corners with red on one end and then black on the others. Only one combination of these worked which leads me to believe that this working combination shows that pin 1 is the one the red lead is attached to.
Did any of that make any sense or am I losing the plot ?


#15

Is it possible just that you are thinking of it backwards? When you view it in Fritzing you are looking through the part from above but when you are testing the pins on your part you are looking from the back which would make them look backwards.


#16

This seems the most likely explaination since the fritzing part’s pin numbers match the schematic in the datasheet you provided.

Peter


#17

Yes - I had taken into account the fact that the component should be viewed from above,
This component actually seems totally non-standard to me, and as far as I can see, the datasheet is not necessarily reflecting reality. I am using this LED matrix to complete projects 21 to 24 in the “Arduino Workshop” textbook. The way that the author connects his up is totally different (and indeed opposite) to the way I had to connect mine up - is it possible that this is just a non-standard component ?


#18

The Fritzing part matches the one on the data sheet marked KWM-R30881AUAB row anode, it is possible you actually have the other varient KWM-R30881CUAB listed as row cathode which would make things incorrect. Can you tell us which part number you actually have?

Peter


#19

Hi Peter
It’s definitely the row cathode (KWM-R30881CUAB) one that I have. I must admit that I had assumed that the datasheet that came with the part was the correct one for the component they provided. Apologies if there was confusion on this. Perhaps this is why I had problems finding the part ? As I said in a previous post, I was dismissing ones that mentioned “common anode”.
Thanks,
Ben


#20

Mostly my fault. The data sheet has both parts, and when the first one matched the Fritzing part I assumed it was correct. I have a 8*8 common cathode part that I can swipe the schematic from and make you a new part in a while.

Peter