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31  Using Arduino / LEDs and Multiplexing / Re: 5x5x5 LED cube help on: January 18, 2013, 02:35:10 pm
But then again diffusing the leds will take the same light output of the led and spread it over a wider beam, so I don't think you gained anything by starting out with 'high brightness' in the first place just to then sand them down Vs getting diffused leds in the first place. However the proof is in the tasting of the pudding so maybe when you are done get a single diffused led of the same size and see if you did indeed gain any overall brightness.

Lefty
yeah, that makes sense. but i guess we'll find out when i get the LEDs. they are supposed to come next tuesday. i'll update you guys with my progress throughout the build. but i am expecting to have issues with coding. i know java so c++ shouldn't be hard to learn. ill probably watch a bunch of arduino tutorials on coding, but i may still need help with coding for the shift registers.
32  Using Arduino / LEDs and Multiplexing / Re: 5x5x5 LED cube help on: January 18, 2013, 02:21:02 pm
i bought 10,000mcd LEDs because i figure i can always make them dimmer with code or resistors, but if i get like 1,500mcd LEDs i cannot make them brighter. CrossRoads also recommended high brightness LEDs. unfortunately they did not come diffused, so i plan on putting them in a drill and using that to sand them down. i know it will be a lot of work, but oh well. i wanted the higher brightness LEDs to be safe and not risk having a super dim cube.

edit: this is the link to the LEDs i bought. i bought 2 lots.
http://www.ebay.com/itm/100-x-3mm-round-Blue-LED-superbright-bulb-lamp-light-/230634491097?pt=LH_DefaultDomain_0&hash=item35b2e30cd9
33  Using Arduino / LEDs and Multiplexing / Re: 5x5x5 LED cube help on: January 17, 2013, 09:25:41 pm
awesome! thank you so much for all of your help! i really do appreciate it! ill try to post pictures of the finished cube when i finish it. i do believe i have all the information i need to feel comfortable ordering parts and not worrying about buying the wrong things.
34  Using Arduino / LEDs and Multiplexing / Re: 5x5x5 LED cube help on: January 17, 2013, 09:20:49 pm
so does that mean i can use the pwm ports on the arduino? i do believe, if i remember correctly, the arduino uno has 5 pwm pins.
*edit: i looked it up and it has 6 pwn pins
35  Using Arduino / LEDs and Multiplexing / Re: 5x5x5 LED cube help on: January 17, 2013, 09:15:52 pm
You are misunderstanding - only 5 LEDs at a time will be on. That's why the discussion of cycling thru the 5 groups, and the 5 layers.
5 x 20mA = 100mA max.
oh ok. now i understand why you broke it up into sections. that makes sense now. so i wouldnt even need an external power supply for this since it will be using very little power. correct?
36  Using Arduino / LEDs and Multiplexing / Re: 5x5x5 LED cube help on: January 17, 2013, 08:40:21 pm
You can drive the anode with 5 arduino pins.  PNP transistors are not needed.
i am now confused. wouldnt that draw too many amps from the arduino? if i have all the anodes of each layer connected and i have 25 LEDs per layer, that would be 500ma per pin from the arduino to power it. am i misunderstanding something?
37  Using Arduino / LEDs and Multiplexing / Re: 5x5x5 LED cube help on: January 17, 2013, 06:36:45 pm
ok, so for driving the LEDs i plan on doing what is described in this video (or something similiar with the ideas recommended by you guys). this is what i was trying to describe before. but i will use a pnp transistor where he uses a MOSFET (because i had a hard time finding those MOSFETS and transistors are much cheaper). skip to about 32:30 in the video to see what im talking about. https://www.youtube.com/watch?v=wVYXAR1GWxU
38  Using Arduino / LEDs and Multiplexing / Re: 5x5x5 LED cube help on: January 17, 2013, 05:21:42 pm
"wouldnt turning on group 1 section 1 turn on that whole section? not individual LEDs?"
Only if the anodes were driven high for all LEDs. Otherwise, just the LEDs with High anodes turn on.

The idea is you enable 1 group of 5 LEDs at a time, a 5x5x5 cube would have 25 groups to cycle thru. 4% duty cycle.
Driving each group for 1667microseconds would yield a 24 Hz refresh rate - leaving over 25,000 cyckes in between writes to do other stuff.
I would imagine a loop within a loop to cycle thru the groups & layers, reading from a 25-byte array (upper 3 bits ignored) to send out a new byte every 1667uS. 2nd array of 5 keeps track of group enable pins, 3rd array of 5 keeps track of layer enable pins.
There are 5 anode drive pins, 5 group select pins, 5 layer select pinsl, so the whole cube is multiplexe with just 15 pins, directly controllable by a single '328P chip with no extra shift registers. Just 15 resistors and 20 transistors.
I didn't make one myself, just helped the original requestor with a design that could be done.
oh ok. that makes more sense. i thought you were saying to have constant current driving the anodes at all times. so you would just have transistors to control the anodes (or an LED driver like you posted earlier)?
39  Using Arduino / LEDs and Multiplexing / Re: 5x5x5 LED cube help on: January 17, 2013, 01:04:42 pm
The first 3 layers are shown. Columns are the anodes.
Each layer is made of 5 groups of 5 common cathodes  - one group of one layer is turned on at a time.
but wouldnt turning on group 1 section 1 turn on that whole section? not individual LEDs?
40  Using Arduino / LEDs and Multiplexing / Re: 5x5x5 LED cube help on: January 16, 2013, 08:11:41 pm
Here it is.
I only did 3 of 5 rows, the other 2 are connected up the same.

i do not really understand that. i understand the logic and how it works, but not how you would implement it in the cube. it looks like it would control each colomns cathode, and then somehow have a second transistor to control the cathode a second time, but it would be based on each layer. i just do not know how you would wire that. maybe i am understanding it wrong. sorry for my questions, i am just trying to learn. as previously stated, i am a noob. i have been messing with electronics since i was a baby, but never anything like this. thanks so much for your help!
41  Using Arduino / LEDs and Multiplexing / Re: 5x5x5 LED cube help on: January 16, 2013, 05:35:11 pm
I know where it is, I had it open to maybe copy part for what I had posted earlier in this thread.
Be home in an hour or so, will post it then.
awesome! thanks!
42  Using Arduino / LEDs and Multiplexing / Re: 5x5x5 LED cube help on: January 16, 2013, 04:15:40 pm
What crossroads says is pretty accurate. Basically what he is saying is that using parts that meet or exceed your needs will reduce your chance of premature failure. You could get away with 595s, they wont break right away, but your needs exceeds the parts specifications, and *may* cause premature failure, and its not the proper way of doing things.

There are actually a lot of ways to solve this problem. I do like your idea of controlling 5 LEDs at a time, and doing that in a loop of 5 that is inside another loop of 5, and you have controlled all 125 LEDs. I dont think that I have seen that one before. It will have an extremely low duty cycle, so It will probably end up very dim, which is probably why we dont see that technique being used. It also means electrically isolating rows, which maybe tricky to make the structure hold up. its still an interesting idea, and may be worth playing around with.

If you limit the current to 8ma to your LEDs with resistors, you could reduce the current to the diodes to 8ma, then you would be within the 70ma max current spec of the 595s, and well within the LEDs specifications.

Another option is to simply run the LEDs and shift registers over spec, and expect to replace them sometime i the future, it can take months to wreck your leds or shift registers. You could build a spare in that time, and have it ready if this one fails.

well, i was going to isolate each layer, not the rows. that way it requires less transistors and less pins on the shift registers. and i was planning on having the layers be the cathodes for the LEDs. but to do that with transistors i would have to use a npn transistor to control a pnp transistor for each colomn. i will try to attach a pic of the circuit. but that is a lot of transistors, a lot of wiring, and a lot of work. lets say i decide to do it completely with transistors and the 74HC595's. What would be the easiest way to do it? keep in mind i do not want to spend a lot of money on this. it is mainly just for learning. it probably will not stay together for very long. after i finish this i am going to make an 8x8x8 RGB cube based off of this one. this one is almost like a prototype so that i know what im doing. thats one reason i do not want to spend much money on it.

basically the circuit is just something i made really quickly. it just shows how i would control the anodes of the LEDs on each colomn. In the Circuit the LED represents a colomn of LEDs. the transistors are just ones that the circuit creator tool had. i will use whatever will work best. same goes for resistors and power. i do still need help on that. i still do not really have a good answer on the best way to power these 3.2v LEDs. any help with that would also be appreciated. thanks for what you have told me so far. everything helps.
43  Using Arduino / LEDs and Multiplexing / Re: 5x5x5 LED cube help on: January 16, 2013, 12:09:42 pm
https://avnetexpress.avnet.com/store/em/EMController?langId=-1&storeId=500201&catalogId=500201&action=products&term=tpic6b595&Nn=25&N=100153+4294956112

78 cents. avnet.com is a US supplier.
I ordered a tube of 20 a while ago. Don't recall what shipping was. You have other parts to buy also?
If not, 74HC595 and NPN transistors will work too.
ok. thanks for the help!
44  Using Arduino / LEDs and Multiplexing / Re: 5x5x5 LED cube help on: January 16, 2013, 01:21:50 am
TPIC6B595 are 83 cents at avnet.com
Who is asking $2 each?
Less likely to make wiring mistakes with fewer parts I would think.


That's what they were asking on eBay. From a US seller, that is. I can get them cheaper from China, but they might take a month to get here. So I only buy from US sellers.
45  Using Arduino / LEDs and Multiplexing / Re: 5x5x5 LED cube help on: January 15, 2013, 10:50:16 pm
I would suggest PNPs for common anode layers, and open drain shift registers, TPIC6B595 type, on the cathode columns.
Can use 5 '595s, 25 for cathode, and 5 to pull the PNP gates low to turn them on.
Each TPIC6B595 can easily sink the 160mA from  8 LEDs all on at once at 20mA if want them good & bright.
that makes a lot of sense and would probably be the best way to do it, but i am on a tight budget. i do not want to spend more than i have to. right now i can get 20 of the 74HC595 shift registers for $5. but it would be $10 to get 5 of the TPIC6B595's. so it wouldn't end up costing much more, but i wouldn't have any spares in case something happened. i am pretty much a noob, so if i accidentally wired it wrong or shorted something out and fried all of the shift registers (or TPIC6B595's) i would have plenty to replace them. but if i bought some TPIC6B595's i would probably buy only a few since they are much more expensive. yes with regular 74HC595 shift registers i will have to buy transistors, but those are extremely cheap and they are always nice to have laying around in case i need them for something or for future projects.
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