http://forums.leaflabs.com/topic.php?id=598 A place to share, learn, and grow... en-US Fri, 22 Jan 2016 00:09:30 +0000 http://bbpress.org/?v=1.0.2 q http://forums.leaflabs.com/search.php http://forums.leaflabs.com/topic.php?id=598#post-3382 Tue, 18 Jan 2011 18:40:18 +0000 gbulmer 3382@http://forums.leaflabs.com/ <p>The natural log of 64 is over 4 (and most things in nature seem to be natural logs :-), so isn't it less than 1/4 the brightness?</p> <p>That aside, if you've tested it, and are happy, everything is fine; that's all that I was trying to alert you to. </p> http://forums.leaflabs.com/topic.php?id=598#post-3374 Sun, 16 Jan 2011 22:20:55 +0000 MessiahAndrw 3374@http://forums.leaflabs.com/ <p>I haven't wired it up since I'm sending my Maple back due to my USB connector coming off. </p> <p>Anyway, the code for the PWM and timing interrupt is done, and I was able to test it with just two LEDs connected being lit at 1:64. The RGB LEDs I'm using are bright enough to make me squint when constantly powered, and also because our perception of brightness increases logarithmically not linearly 1:64 appears to be about a 3rd of the normal brightness. This is acceptable because I'm building a display where I just want to 'pixels' to change colour and not glow. </p> http://forums.leaflabs.com/topic.php?id=598#post-3373 Sat, 15 Jan 2011 21:12:16 +0000 gbulmer 3373@http://forums.leaflabs.com/ <p>Have you wired this up and got it working? Does it look okay?</p> <p>Each LED row will have a mark:space ratio of 1:63, so I'd expect it to be dim.</p> <p>When I've run 8 columns x 16 rows (using a couple of 8x8 LED matrix displays) they seemed noticably dim.</p> <p>So it wouldn't need all wiring up, it'd just need to run the LEDs at a mark:space of 1:63. </p> http://forums.leaflabs.com/topic.php?id=598#post-3362 Thu, 13 Jan 2011 20:55:54 +0000 MessiahAndrw 3362@http://forums.leaflabs.com/ <p>Here you go:</p> <p><a>http://img40.imageshack.us/img40/5043/ledmatrix.png</a> 1208x844 - 54Kb. </p> http://forums.leaflabs.com/topic.php?id=598#post-3358 Thu, 13 Jan 2011 11:19:58 +0000 poslathian 3358@http://forums.leaflabs.com/ <p>wow 960 channels off of 21 GPIO's? can you post a simple schematic? Im not sure I fuly understand how youve managed to pull that off. Very interesting... </p> http://forums.leaflabs.com/topic.php?id=598#post-3356 Thu, 13 Jan 2011 08:53:02 +0000 MessiahAndrw 3356@http://forums.leaflabs.com/ <p>Charlieplexing proved promising at first with its higher LED-count-per-pin (n(n-1) LEDs to pins) that conventional LED matrices, but by binary selecting the row you can dramatically save on pin count (p(2^n)). I use the 15 PWM pins to power the column pixels, and 6 other GPIO to binary select the row to ground (leading to a maximum of 64 rows even though not all rows are used).</p> <p>The system I've implemented allows up to 960 LED channels (I use the term 'channel' rather than 'LED' because I'm using RGB LEDs) even though the number actually used are a lot less. I haven't done a large scale test yet since I need to construct the board the LEDs will be placed on. </p> http://forums.leaflabs.com/topic.php?id=598#post-3344 Wed, 12 Jan 2011 15:26:31 +0000 poslathian 3344@http://forums.leaflabs.com/ <p>Be careful driving current into an output pin. For example if you wire two GPIO's together, both as outputs and drive a 1 into a 0, you risk frying the internal gpio circuitry. </p> <p>If you are trying to drive LED's in a matrix style, I recommend wiring them up with each row sharing a single cathode and each column sharing a single anode - then using one transistor per row to source current through that row, and one transistor per column to drain that current to ground. Err I dont have a diagram but I can provide more info if needed, we did this in an 8x8 grid for some project a while back and it worked fine. </p> http://forums.leaflabs.com/topic.php?id=598#post-3320 Fri, 07 Jan 2011 13:38:01 +0000 soundcyst 3320@http://forums.leaflabs.com/ <p>right, changing the pin direction only comes into play when there are more than two pins in use so that only two pins are source/sink-ing at a time.</p> <p><a href="http://en.wikipedia.org/wiki/Charlieplexing#Charlieplexing" rel="nofollow">http://en.wikipedia.org/wiki/Charlieplexing#Charlieplexing</a></p> <p>if less than two pins are source/sink, then it won't work, and if more than two pins are source/sink, more than one LED will light up at a time.</p> <p>so, my comment above about changing pin directions is really only applicable to the 2-led version </p> http://forums.leaflabs.com/topic.php?id=598#post-3315 Fri, 07 Jan 2011 10:38:15 +0000 gbulmer 3315@http://forums.leaflabs.com/ <p>I don't believe it is essential to change the pinMode when using two pins to drive two LEDs, but it would do no harm when both LEDs are off.</p> <p>It is not essential to change the pinMode of pins when driving a simple matrix of LEDs (single LEDs), but again, it would do no harm.</p> <p>But, I have never found a way to drive a matrix of 'Charlieplexed' LEDs (i.e. LEDs which are 'paired' to be driven with inverted signals) without setting some pins to high-impedance, i.e. INPUT. </p> <p>I think a good place to start is driving 8 LEDs with 4 pins. It is also important to ensure their are no pull-up or pull-down resistors active, otherwise there will be a dim LED glow even when the pin is in INPUT mode. </p> http://forums.leaflabs.com/topic.php?id=598#post-3301 Wed, 05 Jan 2011 14:51:35 +0000 soundcyst 3301@http://forums.leaflabs.com/ <p>yeah, you definitely want them both to be outputs, but you shouldn't need to change the pin mode in the loop.</p> <p>try:</p> <pre><code>void setup() {   //config directions   pinMode(0, OUTPUT);   pinMode(1, OUTPUT);   //init to both off   digitalWrite(0, LOW); digitalwrite(1, LOW); } void loop() { digitalWrite(0, LOW); digitalWrite(1, HIGH); delay(1000); digitalWrite(0, HIGH); digitalWrite(1, LOW); delay(1000); }</code></pre> http://forums.leaflabs.com/topic.php?id=598#post-3297 Wed, 05 Jan 2011 05:31:48 +0000 MessiahAndrw 3297@http://forums.leaflabs.com/ <p>I've solved this problem, rather than use input, I must use OUTPUT_OPEN_DRAIN. </p> http://forums.leaflabs.com/topic.php?id=598#post-3296 Wed, 05 Jan 2011 04:42:59 +0000 MessiahAndrw 3296@http://forums.leaflabs.com/ <p>Hello,<br /> I'm trying to charlieplex a large array of LEDs through the Maple. However to start with I am just trying to control 2 LEDs via 2 pins like in this diagram:</p> <p><a href="http://upload.wikimedia.org/wikipedia/commons/a/ad/Complementary_Drive.png" rel="nofollow">http://upload.wikimedia.org/wikipedia/commons/a/ad/Complementary_Drive.png</a></p> <p>What I tried to do is connect an LED from pin 0 to 1, and another LED from pin 1 to 0, then alternate which is glowing by running:</p> <p>void loop()<br /> {<br /> pinMode(0, OUTPUT);<br /> pinMode(1, INPUT);<br /> digitalWrite(0, HIGH);<br /> delay(1000);<br /> digitalWrite(0, LOW);</p> <p> pinMode(0, INPUT);<br /> pinMode(1, OUTPUT);<br /> digitalWrite(1, HIGH);<br /> delay(1000);<br /> digitalWrite(1, LOW);<br /> }</p> <p>But nothing happened.... I tried using just 1 LED from pin 0 to 1..<br /> void setup()<br /> {<br /> pinMode(0, OUTPUT);<br /> pinMode(1, INPUT);<br /> digitalWrite(0, HIGH);<br /> }</p> <p>void loop()<br /> {<br /> }</p> <p>But still nothing happened.. However by connecting from pin 0 to ground, the LED was able to glow. I ruled out that this was an issue with pin 1, because I tried other combinations of pins and they didn't work.</p> <p>Is there something I am missing, or cannot the Maple do charlieplexing? </p>