Comments on: LED matrix projector

By: Josh

Josh — Wed, 24 Aug 2011 20:51:50 +0000

Where is the code? Is it posted?

By: led

led — Sun, 19 Sep 2010 13:18:21 +0000

thanks Alex, that is what I was suspecting. Is there an alternative to the ULN2803 for the type of displays I have.

By: puzzled

puzzled — Tue, 31 Aug 2010 17:53:51 +0000

has anyone ese got this working from the schematic? Im not a tard and I know how to build from a schematic , I have all the parts and I built it about 8times and it doesnt work. Just wondering before I try again. Nice project BTW

By: smart

smart — Fri, 25 Jun 2010 17:10:26 +0000

Hi! How to fix this:

In function ‘void setup()’:
error: ‘TCCR2A’ was not declared in this scope

I use Atmega8.

By: Paul

Paul — Mon, 15 Feb 2010 16:27:33 +0000

Thanks Alex.

Thats very interesting about the LED duty cycle and current. I didn’t know that.

By: Alex

Alex — Sun, 14 Feb 2010 13:09:36 +0000

Yes, 150 ohm is more reasonable. On the other hand, if you take into account, that every row lights up only 1/8 of the time, you can use higher currents than 20 mA. Most LEDs can be pulsed with 1/10 duty cycle at 1 kHz and then go up to 50 mA or so.
The real reason was, I had these laying around.

By: Paul

Paul — Sun, 14 Feb 2010 04:37:34 +0000

Hi Alex.

Nice Tutorial.

Newbie question though:

Can you tell me why you use 100R resistors please. Don’t they allow too much current through the Red LED’s (according to the spec sheet)?

Here’s my logic…

The shift registers output is 5v and you typically want 20MA @ 2.0V for the red LED’s Therefore the resistor should be
3v/0.02A = 150R minimum

Thanks.

By: Kevin

Kevin — Sat, 06 Feb 2010 21:27:41 +0000

thanks Alex, that is what I was suspecting. Is there an alternative to the ULN2803 for the type of displays I have.

By: Alex

Alex — Sat, 06 Feb 2010 09:01:23 +0000

If you use a common anode, then you can not use the ULN2803, because that chip can only sink current, but not source. That means that chip can not provide current for the anodes of your display.

By: Kevin

Kevin — Fri, 05 Feb 2010 21:40:19 +0000

hi again

I have some Le-mm103 bi-colour displays made by sure electronics. I want to use them in place of the one you used. I think the LE-MM103 is common anode rather than common cathode.

How should I connect it to work correctly

thanks