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91  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 06, 2013, 07:43:02 pm
Quote
Why don't you take a AC voltage reading between your iron tip and an independent path to your power ground when the iron is turned on

In other words take an AC voltage reading with a multimeter between the iron's tip and the grounding in the wall socket?
The iron doesn't need to be turned on the light the LEDs when touching them. I just needs to be plugged in.

I wonder if I can demand changing it in the store because of this... I mean, is this a defect or it's just a poor model?
92  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 06, 2013, 05:37:54 pm
BTW, this is my soldering station: http://www.amazon.co.uk/Basetech-ZD-99-Compact-Soldering-Station/dp/B003A6B27Q
93  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 06, 2013, 05:24:16 pm
Hippynerd, you are so on the spot with your last reply, you couldn't have gotten it more right!! Let me explain...

I started playing with the LEDs tonight, to see how much heat they can take. I took a new LED of the very same type (from the batch used for the cube), I set my iron to 370 Celsius degrees (same as I used with the cube), gave the LED current, so that it would be lit up while I heat it to see exactly after how many seconds it goes out and started heating it... and guess what?! after 35 seconds of constant heating near the head of the LED still no sign of burning out. OK, so I tried it on the other leg for another 35 seconds at 370 degrees. Nothing. No damage. I repeated this about 5 times, abusing the poor LED in a barbarian way, but it's still fine, lights perfectly, no damage. I tried it with one more LED, same result. Heat does not seem to burn them out. At least not in 35 seconds. And I only solder them for 3 to 5 seconds, so that cannot be the cause. I was puzzled... So what the hack was burning them out?!

I went to the garbage can and dug out the 4x4x4 cube that I had tossed yesterday night and started de-soldering the LEDs in order to have more to experiment with. At some point I thought I saw one light up while I was melting the solder near it, but there was no current connected to it, so I thought I was hallucinating or something... but no... it happened again and again.

It turns out that when I touch my soldering iron to one leg of the LED and I put my finger on the other leg, the LED lights! It's a bit dim, but you can clearly see it light. And now comes the interesting part: it doesn't matter which leg I touch with the iron and which led I ground with my body. It lights both ways. I guess that the iron is leaking alternative current and that's why it lights. It's getting 50 Hz PWM current, that's why it's dim. So I started playing with it, touching one leg, than the other. After a few touches it went dead. It's burnt. I tried this with another 5-6 LEDs, but they are fine, I did not manage to burn them out, only the first one gave in. I guess some of them are more sensitive than the others...

This perfectly explains why more and more soldering of the cube burns out more and more LEDs. They are exposed to AC for longer and longer times and eventually they burn out. At first I thought that perhaps my wall outlet into which I had plugged the iron does not have proper grounding (the iron does have grounding), so I took it to another outlet in another room. The result is the same. If I touch the LED with it, it ligths (when I also ground the other leg with my finger).

Now the real question is: what is the problem with the iron? And is it just unsafe for the LEDs or is it also unsafe for me to touch? How can I get around this problem? Should I take it back to the store saying that it's not working properly? Or is this something normal? Assuming that this should not happen normally and that it's not just a problem with my iron, but a problem with all the irons of the same type, what kind of soldering iron should I get instead? What detail should I pay attention to?
94  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 06, 2013, 10:16:54 am
Yepp, that's exactly what happened! The layers were all fine on their own, but when I tried to put them together, all hell broke lose.
BTW, what soldering temperatures do you guys use? 250-300 Celsius degrees? Perhaps more? I've read in several places where people explain how to build an LED cube that they like to use "good hot irons" but only for a second or two. I find it impossible to be in and out in 1-2 seconds, so perhaps a less hot iron would make a difference without increasing the probability of cold solder joints.
I have to find a way to do the soldering with very low probability of burning out the LEDs, otherwise the 8x8x8 cube will put me in the loony bin.
95  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 06, 2013, 08:37:26 am
I've found a really nice experiment here:
http://books.google.ro/books?id=PQzYdC3BtQkC&pg=PA114&lpg=PA114&dq=leds+burn+out+during+soldering&source=bl&ots=8kWGijzk3H&sig=BA_OdSQzM9koZz9J2Vg3Wt-ofyk&hl=ro&sa=X&ei=EVkSUaOoDsKr4ATYnYCYCw&ved=0CFcQ6AEwAw#v=onepage&q=leds%20burn%20out%20during%20soldering&f=false

It explains how you can burn out LEDs while soldering. I'll try it today. I'm curious how fast they fry.
96  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 06, 2013, 06:26:01 am
@Hippynerd: Nice article about soldering!
97  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 06, 2013, 05:25:32 am
Thank you for your answer smiley Well, you did mention that soldering a 3D grid is difficult and I was prepared for that, but what I'm experiencing is way beyond difficult. It's just impossible to work like this. The 4x4x4 cube contained only 64 LEDs and about 10 of them burned out. Dealing with burnt out LEDs in the middle of a 8x8x8 cube would be absolutely impossible, so it's not even worth trying to build it until I can find a way not to burn out the LEDs.

You wrote that several LEDs lighting up simultaneously is due to shorts or opens. Well, there were definitely no shorts caused by LED pins touching wrong parts or by misplaced solder. The only way shorts could have occurred was through burned out LEDs. That was probably the case. I don't know what an LED does when it burns out, does it conduct electricity or not, but it seemed to me that it did. I can't imagine simultaneous light-ups being caused by opens. I mean in my LED cube each LED is connected to a single cathode column, so if I'm not touching that column at all (and I made sure of that!), how can the LED still light up when I'm touching a completely different cathode column with the multimeter's negative tester? The only way I can imagine it through some other burned out LED which conducts electricity...

I talked to a friend about this, who is skilled in soldering and he says that he has abused LEDs several times by soldering them for even 10 seconds, heating them up, etc. and they have never burned out... I don't know what to think. When I arrive home tonight, I'll start heating up some of my LEDs to see how they take the stress. I want to prove to myself that indeed heat is what's damaging them. Perhaps this is a very bad batch of LEDs and I should buy some others...
98  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: February 05, 2013, 07:17:12 pm
I'm afraid I have very bad news smiley-sad

A few days ago I've started working on a 4x4x4 cube to see how I can build it, before I jump into the real one (the 8x8x8 cube). So I drilled a 4x4 matrix of 3 mm holes into a piece of wood to help me assemble the horizontal layers of 4x4 LEDs, filled the holes with 3 mm LEDs, cut the craft wire to pieces of appropriate length and set out to solder the pieces of craft wire to the LED anodes. Now this already turned out to be a huge pain. The craft wire is 0.8 mm thick and the LED legs are way thinner so it's close to impossible to hold them together with clips while you solder them together because the clips will only close to the thickness of the craft wire and will not be able to grab the LED legs properly. Because of this the building process was about 3-4 times slower than I thought it would be. I have wasted hours and hours trying to hold the LED legs together with the craft wire, while I was soldering them. Anyway, after about 8 hours of work I managed to  make 4 layers of 4x4 LEDs connected by their anodes into planes.

While I have built the layers, 2 LEDs burned out or something, because after testing the layers, they were not working anymore, even though they had worked before being soldered into the layers. I didn't think much of it at the time, I just replaced them with new LEDs. But the ordeal began when I tried soldering the cathodes together into columns. Holding the LED legs together with the craft wire was a pain, as usual, but that was the least of problems. After soldering the cathodes of 3 layers together  (into 16 columns), several LEDs started not working and instead they seemed to conduct electricity directly, without lighting up, which resulted in several LEDs lighting up instead of just one when I tested the intersections of layers and columns. In other words, when I put the multimeter's positive lead to layer x and the negative lead to column y, instead of having only one LED light up at (x,y), I saw 2 or 3 LEDs light up. This was not for all (x,y) pairs, just for a few. I managed to find some LEDs which did not light up at all, so I figured that they are the problem. I managed to solder them out and solder new ones in their place through very painful work. Imagine if this would have happened in the middle of a 8x8x8 cube, it would have been impossible to replace them. But the problems were far from over. While I replaced those LEDs, others have burned out. And so on, until I had to throw out the whole darn thing into the garbage. Hours of work gone.

Now the question is: what made the LEDs burn out in massive amounts?
1. My best guess is that they are burning out because of the heat from soldering.
2. My second guess is that perhaps the multimeter's diode testing mode is burning them out.
3. Is there any other explanation?

God knows I've tried to limit the soldering time to 3-5 seconds, with a few exceptions. I can't do it faster, the solder just won't adhere any faster. Maybe the soldering iron is too hot? I think it's a bit above 300 degrees Celsius, although it doesn't show the temperature, so I'm only guessing. Turning it lower seemed not to heat the solder fast enough and I had to keep the iron on the LED legs longer because of this, so it wasn't good either. I've watched several videos about how to solder properly and I'm using standard 40-60 rosin core flux, so I don't think the problem lies there.

This is such a disappointment. After spending 150-200 $ on components and who knows how much time on planning and soldering, I'm close to giving up the whole project because I just don't see how I could avoid these problems. This wast just a 4x4x4 test cube. If just one single LED fails in the middle of a 8x8x8 cube, I'm screwed and my whole work goes down the drain, so I'd rather not even start working on it. The only solution I can think of is to somehow solder the LEDs together with some non-traditional, cold soldering method. Honestly, I've never heard of such a thing, but hopefully it exists, otherwise the whole project is wasted.

Maybe the LEDs that I've ordered are poor quality and weak, maybe they can't take as much heat as regular LEDs? Or maybe I should try soldering at really low temperatures? I doubt that it would work. Maybe I'm burning them out with the multimeter's diode test mode? I don't know. It all seems really hopeless right now...
99  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: January 25, 2013, 05:35:31 pm
Well, all you have to make sure is that the craft wire inside the anode planes never touches any cathodes. The 64 (8x8) cathodes go down and all the anodes are soldered together in the same horizontal plane, including with craft wire. In other words, you solder the LED anodes together along the X axis. You strengthen the anode plane with craft wire along the Y axis (X and Y are in the horizontal plane) and the cathodes go down along the Z axis.
100  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: January 25, 2013, 04:26:37 pm
My intention was to use craft wire only to strengthen the cube where necessary (diagonally relative to the LED anodes, inside the planes), but given the short legs, I might need to make the whole cube frame from craft wire. That would require twice as much soldering, though...
101  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: January 25, 2013, 10:43:08 am
Finally all my parts for the LED cube have arrived (except some minor things that I can start without) smiley I plan to start working on it soon, I will show you pictures when I'll have some results.
The only problem is that the LEDs that I bought seem to have very short legs. The Anodes are 18 mm and the cathodes are 15 mm. It will be a crowded cube...
102  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: December 31, 2012, 03:27:04 pm
Well, I'll sacrifice those 2 millimeters then smiley
Thanks!

BTW, happy new year!
103  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: December 31, 2012, 08:29:06 am
CrossRoads, is there a special reason why the LED cube that we've discussed here uses the cathodes as columns (64 cathode columns) and the anodes as planes (8 anode planes) and not the other way around? Many other cubes that I've seen use anode columns and cathode planes and it seems to be more practical that way because the anodes are 2-3 mm longer, which compensates for the fact that the LED heads are taller than wide, so the horizontal and vertical distances between the LEDs could be longer and still equal if we used anode columns and cathode planes. Is it possible to do this reversing of anode/cathode roles? If yes, how?

Thanks,
Andras
104  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: December 31, 2012, 03:09:27 am
Hi!

I'm planning to run 64 20 mA LEDs from one of those MOSFETS.
That price of 142$ includes components for the big 8x8x8 cube, but also for the small 4x4x4 learning cube and some spares. I guess that if I tried to but onyl as many components as necessary for the 8x8x8 cube only, I could have pulled it off for about 100$.

6m of craft wire is definitely not enough. But I have bought 3x6=18m, which is probably twice as much as I need. I do not know how soft or hard it is, I bought it blindly from eBay based on the suggestion of somebody who has already used the same or similar craft wire to build a LED cube successfully. It is 0.8mm thick and is sold rolled up, I'll have to straighten it before soldering.
105  Using Arduino / LEDs and Multiplexing / Re: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 on: December 30, 2012, 06:38:47 pm
For anyone else who might be interested in the future to build a LED cube based on this design, I've put together a component list with prices based on what I have bought for the project. I tried to buy the components as cheap as I could, most of them off eBay, but for many of them I have bought more than actually necessary, because they sell in bulk or because I wanted some spare parts. Here's what I got:

NDP6020P: 14 pcs 33.3 EUR (43.8 USD)
3mm diffused blue LEDs: 1000 pcs 19.4 EUR (25.5 USD)
TPIC6B595N shift registers: 20 pcs 9.3 EUR (12.3 USD)
1K variable resistors: 100 pcs 7.4 EUR (9.8 USD)
5V 3A power supply: 1 pcs 7.1 EUR (9.4 USD)
Craft wire 0.8mm 6m: 3 pcs 7 EUR (9.2 USD)
Jumper cables 40 PCS: 2 pcs 6 EUR (7.9 USD)
Capacitors (0.1 uF) + resistors (82R, 220R): 3 pcs 4.6 EUR (6.1 USD)
PCB 18x12 cm: 2   pcs 3.9 EUR (5.2 USD)
Female pin headers: 200 pcs 3.8 EUR (4.9 USD)
TO-220 heatsink: 10 pcs 3.4  EUR (4.5 USD)
IC sockets DIP-20 for TPIC6B595N: 10 pcs 2 EUR (2.7 USD)
Crocodile clips: 2 pcs 0.8 EUR (1 USD)
Total: 108 EUR (142.3 USD)

Sorry, I just can't get the data into a well-formatted table.

This does not include, of course, the price of the Arduino driving the cube or other miscellaneous stuff like soldering materials or the prices of some tools that you use for other projects too.
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