LED Matrix kit, what would you prefer 8x8, 16x16, 8x32...

[Sceadwian]

3 bytes? A 7x24 matrix is 21 bytes..

Souper. An 8x8 module that has an output into the next modules input that uses latching registers could be made as large as the update rate allows. For each extra module you add the update rate would just get slower.

Economy of mass, it would probably be very cheap to assembly the individual modules into a matrix of any size desired.

 

[blueroomelectronics]

Sorry I meant 3 bytes wide. You're right 21 bytes.

 

[Mike - K8LH]

How about modular boards that allow you to put together any size matrix? You've probably seen the modular 8x8 design below before... Instead of putting all of that logic on each board, just put a 20 pin dual row connector. The important thing would be to design the boards in such a way so that they could be mounted onto a frame with no LED gaps between boards.

 

[Sceadwian]

That is exactly what I had in mind Mike.

 

[Marks256]

Hmm. i like that idea, but how expensive would it be?

 

[blueroomelectronics]

The 8x8 would make a nice kit but its lack of built in cpu means it would be a slave to some other board.

Hand wiring scads of LEDs by is not fun nor durable. And by not using too many LEDs makes the kit affordable and simplifies the both the driving circuits and power supply.

The 7x24 would allow for four 5x7 letters (with 1 space between) and looks like a nice size, I would have liked 8x24 but text seems to be the use of choice.

Since the design uses normal 5mm LEDs it will only be seemlessly expandable side by side. 24LEDs running at up to 60ma each can draw nearly 1.5 amps so a switch mode regulator may be called for, but a linear is cheaper and more common an will run hot. Reducing the current per LED will help, 30ma @ 1:7 duty will be bright even with standard LEDs and draw a less costly 770ma

 

[Suraj143]

Reducing the current per LED will help, 30ma @ 1:7 duty will be bright even with standard LEDs and draw a less costly 770ma

Hi in LED matrix circuits what is mean by duty cycle? Is it the number of times the scan calls or else....?

I mean like this

call SCAN
call SCAN
call SCAN

Thanks

 

[blueroomelectronics]

Hi in LED matrix circuits what is mean by duty cycle? Is it the number of times the scan calls or else....?

I mean like this

call SCAN
call SCAN
call SCAN

Thanks

To keep the number of wires and amount of current required resonable you only turn on 1 row of LEDs at any given moment.

So for a panel of 7x24 LEDs you'd select column 1 light your row leds (24 in this case), leave on about 2ms the turn them off, go to column 2 and repeat. It would take 7 passes to complete so a row of LEDs are only on almost 1/7 of the time. You need to get the LEDs as bright as you can as they will be dimmer than if they were directly driven. Often you can boost current beyond the normal rating of the LED to get peak brightness.

Here's an article on the process
https://www.best-microcontroller-projects.com/led-dot-matrix-display.html

 

[Mike - K8LH]

Another important design consideration is Refresh Rate which is how often each LED is refreshed or scanned each second. So for Bill's 7 row display scanned at 2 msec per row you'd have a 1/7th or 14.29% Duty Cycle and a 71.43 Hz Refresh Rate (each led is scanned or refreshed once every 14 msecs --> 1/0.014 = 71.43 )...

 

[Mike - K8LH]

Here's another design for your consideration. You could certainly use discrete LEDs instead of 5x7 matrix displays. And, populate it with LEDs and drivers as you see fit.