Visibility large Led-display.

Other Hardware LEDs and Multiplexing
1

Hi,
I've become volunteer at a fablab in my city, that opened its doors a few months ago. There is a lot of activity, but the big public still doesn't know us yet. To create some buzz, I'd like to build a huge, simple, interactive led display.

Situation.
The fablab itself is located close to the center of town in a public library, directly facing a 50 mtr wide (150ft) canal. Loads of people walk on the other side and I can use 2 windows (total dimension 4x2.40 meter or 13x8 feet) to create my display. Luckily the windows are in the shade most time of the day. I also found a shop right across the canal, where I can store a device to relay data.

Goal.
Display will be used partly to give some... info about the Fablab and perhaps to show time/temperature. The idea is not to display loads of info, but basically to tell there's a fablab in the building.

To create a buzz, I'd like to add a game of pong, which people can play using their mobile phones.

50mtrs is quite a lot to read detailed info without 20/20 vision, I need to think about cost as well and I won't be creating a zillion-pixel display. The idea is to build a 16x24 (or 16x32) pixel display.

Question...
Having played with normal and power leds, I know they can emit a lot of light, but I'm not sure what kind of leds/setup would be best/good enough for a project like this.

Using addressable leds, like the ws2812, would be nice since it's easy to build, with the possibility to light each led full time. I could also use brighter leds and a row-scanning technique to display 2 rows at the same time, but I wonder what the result will be since each led will be on for 1/8 of the time max.

Perhaps both techniques could be used fine, only having experience with a small 16x24 indoor display, I'd like to know more before I start to build, to avoid wasting time&money.

Thank you in advance for all the help you can give me.

2

Forget it!

Go find the biggest second-hand computer display you can, or buy an Aldi TV, and hook it up to a Raspberry Pi.

Much, much cheaper and almost as effective.

3

Go find the biggest second-hand computer display you can, or buy an Aldi TV, and hook it up to a Raspberry Pi.

It doesn't convey much of a DIY/fablab idea, does it?

4

You could build a 1.2m long, 125x16 bi-color display, by using 4 cascaded 32x16 5mm LED displays from Sure, available for about $35 each. They can be easily controlled by an arduino. You can even play tetris on it (one person at a time though), through BT.

5

florinc:
It doesn't convey much of a DIY/fablab idea, does it?

Considering the ubiquity of large full-colour LED matrix displays such as that on my local Coles supermarket, the Catholic church (though that may still be RG only) and the car-wash, not to mention all the roadside "trailer" units in Sydney, that may be moot.

The clear advantage of the LED matrices over LCD is their brightness.

6

@Paul__B
I'm afraid a large TV might still be to small, but I noticed the library has a large unused TV, I will test it.

A led display using top notch leds, tip top enclosure etc will indeed cost a lot.

I noticed mouser already sells 0.5 watt Osram leds for 12-16 cents per led, I found a local site selling 3 watt cree leds for ~$1 a piece as well and there's always Ebay. I don't want to save money on electronics required to drive the leds, I rather not buy at Ebay, but would it be impossible to build a reliable display for 400-700 dollars ?
I probably can still buy a very nice 2nd hand TV for that, but if one TV is to small the next step is 4 and I do have space for ~16 47inch displays already.

I have no experience with this size of led display though, what kind of prices do you think a 13x8 feet, 16x32 pixel, no labour cost, led display would cost me ?

@florinc,
Tetris would be nice as well, but I'm afraid blocks will have to drop from left to right with the windows I've got :slight_smile:
I have built two dotkloks using the sure HT1632 displays you mention.
Besides a pong-clock it has a funny "time eating" pacman-routine, that I'd like to use. These clocks also gave me the Idea for what I'd like to do now. I'm living in a town with 60.000 inhabitants, not las Vegas and guess the possibility to actually play a game could create the buzz.

Closest distance for my project is 50mtrs though. The sure displays itself, 5x10 inch max., are far to small and can already be hard to read on a sunny day indoors.

7

How about this - Parola library driving MAX7219s, with extra drive circuitry for the higher power LEDs per the attached App note?

MAX7219-MAX7221.pdf (451 KB)

MAX7219-7221 AppNote AN1196.pdf (42 KB)

8

maybe you could use regular 100w bulbs and solid state relays.... then, for the pixels you could make squares to put the bulbs in with a diffuser on the front.

that would take care of the brightness problem, and a 100w bulb and socket is cheap.

no rgb though....

9

Thank you for all the advice, unfortunately I'm not much closer yet.

I've started building 3x3 displays of different sizes. I do have quite a number of leds with different powerspecs and am going to do some empirical research to check what brightness/screensize I need. I've made some files I can display on the TV as well.