Which Type of LED 8 x 8 Matrix for an led display

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elec93

New Member
Hello,

I want to make an LED display consisting of 4 8x8 matrices (to display scrolling text) but being an idiot I can not work out whether common anode or common cathode matrices, I would be very grateful for any advice.

I was planning to a 18M2 with Max7219s but I am struggling a bit with the circuit, are there any published circuits I could refer to?

Thanks

Elec93
 
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westaust55

Moderator
I was planning ...
Click to expand...
It is better to first decide how you are going to control the 8x8 matrix.
If with discrete components and more code in the PICAXE then you have transistors whether ULN2803 and individual transistors or similar then it does not matter greatly if the LEDs are CC or CA.

If you elect to use a dedicated controller chip then the LED type must match the controller chip requirements.
 
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elec93

New Member
Thanks eclectic,

I have followed the links and it does give me some insight especially with the circuit but I am still completely stumped on how to code the multiplexing.

Never a bright spark

elec93
 
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westaust55

Moderator
Have you looked at the thread I linked to and the Datasheet.
The code as provided is the basic code and you just need to send more data for a matrix as opposed to a 7-seg display.
Without knowing your schematic wih exactly how you have connected the hardware folks here cannot provide an exact piece of code.

The code in my link sent raw data for 4 hex digits in the second part as if it was a 4x 8 display. You need to send twice as must data for an 8 x 8 matrix.
 
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elec93

New Member
Hi Westaust55,

Thanks for your input. Unfortunately I haven't been able to attach a circuit diagram, incompetence strikes again, the circuit I have is a Pixaxe 18M2+ connected to 4 8x8 matrices which are common cathode (the anodes are joined together to formed the rows). The 18m2 is connected to the anodes via a 74HC595 and appropriate sized resistors. the cathode are connected to transistors and then to a 74HC595 (there are 4 of these linked together) which are connected to the the 18M2.

The problem I have is first I have realized that I do not fully understand the sequencing to get a series of lit columns (with different patterns) to scroll across the matrix.

Secondly I am not that experienced with programming having only done some basic programming at the start of the home computing age, yep I am old.

I made a promise to some one very dear to me to make this so any help would be very appreciated.

Many thanks

Elec93
 
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westaust55

Moderator
elec93 said:
Unfortunately I haven't been able to attach a circuit diagram
Click to expand...
To attach a file, with a post window open for a new post or to edit, you can use the paperclip icon in the top row (towards right hand side) of the post edit window toolbar.

If the icon is not visible then click on the "Go Advanced" button at the bottom right of the post edit window (near the "Submit Reply" button)
 
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westaust55

Moderator
elec93 said:
Unfortunately I haven't been able to attach a circuit diagram
Click to expand...
To attach a file, with a post window open for a new post or to edit, you can use the paperclip icon in the top row (towards right hand side) of the post edit window toolbar.

If the icon is not visible then click on the "Go Advanced" button at the bottom right of the post edit window (near the "Submit Reply" button)

To drive/write the data into the 74HC595 chips with a PICAXE M2 part you will need to use a subroutine such as that in PICAXE manual 2 at the end of the SHIFTOUT command.

Are you intending to scroll the message one column of LED's at a time or 8 columns at a time.
Both are possible but scrolling one LED colum at a time will be more complex to achieve.

Suggest that you look to getting some static display workinjg first and then add code for scrolling as the second step.
 
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