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Am working on a project where in I had to control 169(13x13) LEDs, I chose ATMEGA 2560 processor for this task but it has absolute maximum Source and sink values as 200ma which was not sufficient. I did some research and found one can use Shift registers, LED drivers but I don't understand those stuff.

I found a solution for my source loading problem i.e to use Voltage Follower(using Opamp) which takes very less current from pin and delivers more current to the load thus reducing burden on the pin.

Now I need to sink the current to processor, I know I can't sink so much current in ,,it will damage the processor,,,now I need to reduce the current coming into the pins without lose of LED brightness since increasing resistance value will reduce the brightness as well as current

All suggestions are welcome.

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    \$\begingroup\$ I don't think using 26 op-amps would be a good idea. If you don't understand much about this I would recommend using a specialised LED matrix driver board which would take care of everything, addressing and power supply. Otherwise have a look at this: instructables.com/id/LED-Matrix-with-Arduino \$\endgroup\$ Commented Aug 21, 2015 at 9:49
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    \$\begingroup\$ Using 2 ICs (shift register + led driver) is simpler than 13 or 26 Op-amps instructables.com/id/LED-matrix-using-shift-registers \$\endgroup\$
    – Oka
    Commented Aug 21, 2015 at 10:08
  • \$\begingroup\$ hey i got the solution i think use ULN2803A IC to sink the extra current instead of reducing it,,,,am i correct??? \$\endgroup\$
    – Lokanath
    Commented Aug 21, 2015 at 10:08
  • \$\begingroup\$ Yes, you can use 2803A or any transistor array. \$\endgroup\$
    – Oka
    Commented Aug 21, 2015 at 10:10
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    \$\begingroup\$ Without shif register, you need do multiplexing by software. You can use 13 transistors (or transistor array IC) and 13 resistor. See schematic here: hackaday.com/2010/10/26/70-led-matrix-in-a-jack-o-lantern \$\endgroup\$
    – Oka
    Commented Aug 21, 2015 at 10:20

1 Answer 1

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Assuming the Opamp is chosen correctly, meaning that it can go to ground with a single power supply (not split supply). Then both ends of the matrix can be buffered with Opamps. There are two caveats though. The first is that most op amps that I've seen can't source more than 100mA at a time and that would make them poor line drivers. The second and more obvious reason this setup would require 26 Opamps to complete.

A different suggestion would be to use Mosfets as line drivers and Opamps combined with BJTs as constant current sinks. This would reduce the loading on the micro and eliminate the need to use resistors for the LEDs.

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