LED matrix questions

Design Concepts
1

Ok, no replies, lets try again…

Darlington array’s or not?

the original BLM doesnt require these, but the protodeck uses ULN28003 darlington array’s and BC547 NPN transistor’s. i have seen posts where people say you can not provide enough power with out these, but the BLM seems to work with out it.

anyone have any input?

Original post:

Im working on a LED matrix, just standard Red LED’s designed in Eagle CAD to go under my Nintendo DS touch screen (when i get it working <___base_url___>/index.php?/topic/12950-controlling-pic-pins/&do=embed)

Im using a PIC18f452, custom coding my MIOS app. DOUTx4 board for the LED’s and i would rather use an LED matrix than 2 DOUTx4 boards.

Have a few questions.

  1. the Protodeck uses ULN28003 darlington array’s and BC547 NPN transistor’s, but the MB 6582 SID doesnt use them for the LED matrix. Are these required?

  2. I was thinking of having 2 LED matrices one which is 8x8 red LED’s, and another that is 2x8 LED’s. is it possible to treat this as one 10x8 matrix?

  3. anyone with experience in PCBs, is my design ok? the LED’s are on one side, and the resistors are on the bottom.

  4. the DIL’s pinning for the LED’s are not what the BLM code expects, is it easier to change this in the code to the correct order? or by the wires going from this board, to the DOUT board?

cheers,

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2

bump… anyone have some more info, im lost at the moment.

3

The MB-6582 does use BC547 for sinking both common cathodes of LED “columns” (up to 16!) and also the switch in the switch matrix.

I just posted why here: <___base_url___>/index.php?/topic/13916-led-matrix-column-dimming&do=embed

They aren’t always required, it all depends on how many LEDs you want to use, their brightness at low current levels, how much current will be sinked by one DOUT pin, etc. You can get away with no transistors (re sammichSID) or play it safe and put them in.

I used BC547 instead of Darlingtons because the collector emitter voltage of Darlingtons would be too high for use in a switch matrix, i.e. the voltage at the DIN input if I used Darlingtons would be close to or maybe over the logic low voltage threshold, depending on current sinked through the Darlington.

4

about the design, you could check my protodeck’s page.

this one could help too: