Led Driver Selection/Option - Page 1
Forum section: electronics / beginners

author: bitman
author_rank: Unknown
timestamp: December 28, 2018, 06:07:42 pm
content: I think I may be going down the wrong road here - I need to drive a simple cube of LEDs (I know, that was something done 2-3 years ago - what can I say, i'm slow). I have 16 input, and 4 common leads. Very simple - just need to multiplex on the common.The issue I have is finding led-driver chips. Right now I'm driving it from an Arduino Nano and some OLD 74HC595 and it's just too slow or rather, since I have to use the Arduino to constantly multiplex it just cannot keep up with updates, multi-plexing etc. so I think I need to use an LED driver where simple flipflops and a on-chip multiplex will allow the processor to just deal with sending updates.The MAX7912 and my old AS1108 all are 8 bit and initially I wrongly assumed I just would use two of them to get 16 bits, but I cannot share the common leads this way. And that's where I am running into a wall. Searching Digikey I can easily find drivers for 16 pins or a lot more, but what I cannot find a way to do is specify the number of common pins. So I think I'm hunting for a dumb and uncommon solution. If I separate the commons so each driver chip would have it's own, I would loose the stability of the cube design as it stands right now - I don't want to treat the cube as I would a set of 7 segment displays that are all isolated. The idea is to control the multiplexer across the whole cube not treating it as several small devices put together. The old designs out there seem to share this idea too.Since my cube is very small I didn't expect there to be a need for a lot of chips. Well, since I'm not using the driver right now I have plenty of transistors - another reason I am looking for a LED driver instead.My hope is that there are drivers with more common leads too. Or is the solution to use 4 chips like STP16CPC26 and use the controller to multiplex between them? It seems it's only half a driver since it doesn't deal with the multiplexing at all.So I'm a bit lost about the right approach here. I had hoped that I could get two AS1108 going, very simple - but they cannot share the common leads (that I know of). So what's a better approach? Note, this is again a learning project. Besides the multi-plexing i'm also looking to get my current requirements right on this. So I really am not looking for "follow this instructable" - I am hoping to come away from this crazy simple project a little more knowledgeable.

author: mvs
author_rank: Frequent Contributor
timestamp: December 28, 2018, 09:27:01 pm
content: You have not written what you consider as common in your matrix, anodes or cathodes...TM1640 can drive 8 anodes x 16 cathodes matrixHT16K33 (in SOP28 package) and TM1629A can drive 16 anodes x 8 cathodes matrix

author: nsrmagazin
author_rank: Regular Contributor
timestamp: December 29, 2018, 02:17:02 pm
content: Commonly they use a microcontroller:https://www.instructables.com/id/LED-Cube-4x4x4/

author: bitman
author_rank: Unknown
timestamp: December 29, 2018, 05:45:42 pm
content: Quote from: nsrmagazin on December 29, 2018, 02:17:02 pmThanks - that's definitely an option - that said, I did start this quest thinking an ATTINY would do since we're simply talking about a latch hat's updated at a very low frequency. While I could definitely put in a ATMEGA16/32 and use all available it would end up "very busy" and eating more than just a simple clock switching the active latch? But I do actually have a few of these chips loose so perhaps I should consider redesigning this way. Another difference I see is that i have transistors on both sides of the LED - the controller has no data points that directly drive the current to the small cube.But I have to admit that beside a bit more complex code to make the refresh of the array and updating the "latches" this may be a simpler method than using a LED Driver.Thanks. Food for thought.

author: bitman
author_rank: Unknown
timestamp: December 29, 2018, 05:51:57 pm
content: Quote from: mvs on December 28, 2018, 09:27:01 pmSo my question is still how to find these? I can search on the "segment" leads but I couldn't find a way to indicate "GRID" - it seems TM1640 is pretty close if not a perfect match to what I set out to find but weren't able to. I could find a lot of chips with lots of "segment" lines but all based on a single common ground or VDD - so i would need one per section. I didn't want to do that. Thanks for the suggestions - I'll look closer at the chips. I wish my "component foo" was closer to my level of "google foo" ... well, live and learn.

author: agehall
author_rank: Frequent Contributor
timestamp: December 29, 2018, 07:15:34 pm
content: Are you going for a simple on/off setup for each led or do you want grayscale control over each LED?I'm looking at building a couple of LED cubes myself during 2019 and I'm looking at the TLC5940 or something along those lines to drive it so that I can control the brightness of each LED.

author: nsrmagazin
author_rank: Regular Contributor
timestamp: December 30, 2018, 06:50:07 am
content: Here is my guess:The MCU might not be enough to supply current for a whole layer of LEDs(16 LEDs), especially when we consider the length to the LEDs(wires). However an atmel mega or arduino should be able to supply 40mA which is enough, otherwise you will need a transistor because some of the LEDs will not light. The battery will hold "1000mAh / 40mAh = 25 hours".You can see how its done here: