Basically a three foot tall digital clock. Four 7-segment displays.
I think it would be a good idea to start off with a single LED for each segment and then scale it up once I can make LEDs work. Pretty much everything I have seen uses multiplexing but that won't work because I will ultimately be using relays and LED strips for each segment (unless someone has a better suggestion).
7 x 4 = 28, so I will need at least 28 outputs.
I have never used an arduino before but the Mega seems to be what I am looking for? Since I don't need seconds, accuracy within 60 seconds should be good enough but I think it will be better than that. I've seen the wifi shield so maybe later I can expand for auto setting and DST. I think I need an RTC (how do I pick one)?
I have an automotive background, I've been through two C++ classes and am currently enrolled in assembly but I have never tried anything like this.
For multi-led segments, you will likely use LED strips, which are generally 3 LEDs in series with a current limit resistor. If the segments are 3,6,9,12 LEDs long they are strings of 3 LEDs in parallel. Current will be ~20mA for each 3-LED string.
TPIC6B595 shift register is awesome for driving LED strips like that. High current capable, and the strips are generally powered from 12V.
This board I offer drives up to 12 digits. http://www.crossroadsfencing.com/BobuinoRev17/
CrossRoads:
TPIC6B595... High current capable, and the strips are generally powered from 12V.
Bob, the OP wants to build digits 3ft high (~1m). If the LED strips are 60 LEDs/m, I estimate each segment will be around 30 LEDs, so current could be 30 * 20mA / 3 = 200mA.
Will TPIC6B595 be overloaded if the display is not multiplexed? Would TPIC6A595 be a better choice in this case? Can your board be populated with the 20pin version of TPIC6A595?
3 feet high = 1.5 foot segment = 18 inches, 6 triple LED segments? 180-200mA sounds about right.
In that case, this board would make more sense, 32 drivers = 4 digits with 1A/segment.
Holes for mounting Uno right on the board.
There's a couple clips of it driving 9-LED strips on the website Cross Roads Electronics, scroll down to just after the '1284 boards.
Would someone mind posting a link to the triple LED segments you are referring to?
If 6 of the triple LED strips need ~200mA and the board will do 1A per segment, then I should be able to add more than the 6 correct? I was thinking of doing wooden boxes with diffusing panels for each segment to make it glow. Do you think the 6 strips per segment will be bright in a well lit room?
toylocost:
So I need an UNO, and CrossRoads' board...
That's one option. Others include:
using a Mega (so no shift registers are needed) and 32 MOSFETS
using an Uno or Nano 3 and 4 TPIC6A595 chips
toylocost:
Would someone mind posting a link to the triple LED segments you are referring to?
We are referring to the ordinary 12V led strips you can buy on reels from a thousand sellers on eBay for example. On these 12V strips, the strip can only be cut after every 3rd LED. That's because each trio of LEDs is wired in series, with a resistor, to the 12V supply.
toylocost:
If 6 of the triple LED strips need ~200mA and the board will do 1A per segment, then I should be able to add more than the 6 correct?
Yes, quite a few more. But I'm not sure you will need them.
toylocost:
Do you think the 6 strips per segment will be bright in a well lit room?
6 strips of between 18 and 30 LEDs per segment will light an entire room by themselves! Especially if you are not multiplexing the digits.
One strip of between 18 and 30 LEDs per segment should be more than bright enough for indoors. Maybe too bright!
If using TPIC6A595, the maximum current would be 350mA per segment, which would limit you to around 54 LEDs per segment, so the digits would be around 6 feet high. With 1A MOSFETs, each segment could be as many as 150 LEDs, which would be digits over 12 feet tall!
Check me if I am wrong, but CrossRoad's board would do 1 LED per segment while you generate the program. then as you assmbled your full scale unit, all you need to do is to wire your LED's accordingly.l
If you want to control lots of three-color LED's, why not use the NeoPixel strips sold by Adafruit, or similar strips found on EBay? They come in various lengths, but you can power and control them using only Gnd, power, and one communication line.
My board will drive 1 LED per output, or 1 segment of 3, or multiple segments of 3, for example here's eight 9-LED strips http://www.crossroadsfencing.com/BobuinoRev17/MVI_2864.AVI
so can easily scale up in size. 1 segment of 3 would be easiest for development as the current limit resistor is then included.
Can also send PWM signal to the board to control the OE/ pin on the 'HC595 for brightness control while testing, like here Arduino Power! - YouTube
Can arrange the strips to use 2 or 3 side-by-side in each segment if you want fatter, brighter segments.
Just remember that you will use ~20mA for each 3 LEDs. A 15-LED segment then needs 100mA -> 700mA for a digit -> 2.8A for 4 digits. 30-LED segment, either really tall or double-width, then needs 5.8A.
3-color LEDs was not a requirement.
The Neopixel/RGB LEDs have the disadvantage of consuming a lot more power - You can't power from 12V for example and have 3 LEDs in series share the same 20mA.
