Comments on: LED matrix projector http://tinkerlog.com/2008/08/31/led-matrix-projector/ Alex' blog Wed, 10 Mar 2010 23:29:18 +0100 http://wordpress.org/?v=2.8.6 hourly 1 By: Paul http://tinkerlog.com/2008/08/31/led-matrix-projector/comment-page-1/#comment-95899 Paul Mon, 15 Feb 2010 16:27:33 +0000 http://tinkerlog.com/2008/08/31/led-matrix-projector/#comment-95899 Thanks Alex. Thats very interesting about the LED duty cycle and current. I didn't know that. Thanks Alex.

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

]]> By: Alex http://tinkerlog.com/2008/08/31/led-matrix-projector/comment-page-1/#comment-95828 Alex Sun, 14 Feb 2010 13:09:36 +0000 http://tinkerlog.com/2008/08/31/led-matrix-projector/#comment-95828 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. ;) 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 http://tinkerlog.com/2008/08/31/led-matrix-projector/comment-page-1/#comment-95797 Paul Sun, 14 Feb 2010 04:37:34 +0000 http://tinkerlog.com/2008/08/31/led-matrix-projector/#comment-95797 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. 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 http://tinkerlog.com/2008/08/31/led-matrix-projector/comment-page-1/#comment-95443 Kevin Sat, 06 Feb 2010 21:27:41 +0000 http://tinkerlog.com/2008/08/31/led-matrix-projector/#comment-95443 thanks Alex, that is what I was suspecting. Is there an alternative to the ULN2803 for the type of displays I have. thanks Alex, that is what I was suspecting. Is there an alternative to the ULN2803 for the type of displays I have.

]]> By: Alex http://tinkerlog.com/2008/08/31/led-matrix-projector/comment-page-1/#comment-95413 Alex Sat, 06 Feb 2010 09:01:23 +0000 http://tinkerlog.com/2008/08/31/led-matrix-projector/#comment-95413 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. 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 http://tinkerlog.com/2008/08/31/led-matrix-projector/comment-page-1/#comment-95387 Kevin Fri, 05 Feb 2010 21:40:19 +0000 http://tinkerlog.com/2008/08/31/led-matrix-projector/#comment-95387 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 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

]]> By: Alex http://tinkerlog.com/2008/08/31/led-matrix-projector/comment-page-1/#comment-94591 Alex Sun, 24 Jan 2010 17:36:00 +0000 http://tinkerlog.com/2008/08/31/led-matrix-projector/#comment-94591 Hi Kevin, attach the left pin with GND, the right pin with VCC and the middle pin with analog port 0 (zero) of the Arduino. Cheers, Alex Hi Kevin,
attach the left pin with GND, the right pin with VCC and the middle pin with analog port 0 (zero) of the Arduino.
Cheers,
Alex

]]> By: Kevin http://tinkerlog.com/2008/08/31/led-matrix-projector/comment-page-1/#comment-94586 Kevin Sun, 24 Jan 2010 13:10:08 +0000 http://tinkerlog.com/2008/08/31/led-matrix-projector/#comment-94586 Hi Your schematic does not show how the 10K pot is connected, please can you advise. Thanks Hi

Your schematic does not show how the 10K pot is connected, please can you advise.

Thanks

]]> By: shamay http://tinkerlog.com/2008/08/31/led-matrix-projector/comment-page-1/#comment-91988 shamay Wed, 16 Dec 2009 07:48:38 +0000 http://tinkerlog.com/2008/08/31/led-matrix-projector/#comment-91988 great project! what other projects regarding led matrix display can you suggest BUT using analab2.0? great project!

what other projects regarding led matrix display can you suggest BUT using analab2.0?

]]> By: 64 Pixels Roundup | Interactive Matter http://tinkerlog.com/2008/08/31/led-matrix-projector/comment-page-1/#comment-77853 64 Pixels Roundup | Interactive Matter Wed, 20 May 2009 17:26:10 +0000 http://tinkerlog.com/2008/08/31/led-matrix-projector/#comment-77853 [...] Tinkerlogs Led Matrix Projector [...] [...] Tinkerlogs Led Matrix Projector [...]

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