Picture of Build a huge 7 segments 8 digits red LED display
This instructables presents how to make a huge 7 segments 8 digits LED display panel. The purpose of this display is to display the time, date, temperature or to be used as a chronometer at various running contests, mountain bike contests, trail running contests and so on (organized by NGOs with low budget). The display may show elapsed time (hours, minutes, seconds and hundreds of a second). In order to use the display, a microcontroller or digital interface is needed and this is above the scope of the current instructable.
The display may work as a stand alone device driven by a microcontroller (Arduino stuff) or may be driven by a PC / laptop (interfaced by some discrete digital logic).

Design constrains / requests:
-to be big enough to be readable from 20-30 meters
-to be bright enough to be visible / readable in sun light
-to use energy efficient light emitting devices (bulbs, LEDs) / (low electrical power consumption)
-to use feasible and long lasting light emitting devices
-to withstand to harsh environment (some contests may be during fall, winter times, during rain, strong sun)
-to be light and sturdy in the same time  (it has to be carried from point A to B)
-to have a reasonable size in order to fit on regular vans or on the roof of a car - it must be carried from a location to another
-to show hours, minutes, seconds and miliseconds (hundreds of a second) as a chronometer
-to show as well the temperature (negative and positive), local time and current date
-to separate the pair of digits by ":"  - 2 separation dots
-to allow multiplexing of segments and digits and separate control of minus and separation points
-to have a reasonable cost
-to involve a reasonable amount of work
-to look nice

Based on these requirements, my choice was to use red LED strips for 12Vdc (these are comming in reels and you can cut the desired length), polycarbonate panels and a wooden frame. All the LEDs were connected using cheap network cable (8 wires inside, full copper).
The LEDs were connected to form 7 segments per digit and 8 digits (6 digits are big size and 2 digits are small size (these 2 digits are used to display hundreds of a second)). Also in front of the first digit is a big minus sign (for negative temperatures) and between each pair of digits are 2 separation dots.

Tools needed:
-wire cutter (wire desoldering tool is nice to have)
-soldering iron and related tools for electronic parts soldering
-drilling machine and drill bits
-wood saw (any, you need to cut wood a few times)
-brush to paint
-silicone pistol
-hot glue pistol
-printer to print A4 sheets
-others (?!)

Materials needed:
-red LEDs - 2 reels at 12Vdc with adhesive back tape, one reel is 5 meters or 300 red LEDs  (update 2014: you can look for LED reels with 120 LEDs per meter, the result is improved, see here another nice project: Giant Two-Digit Countdown Clock)
-polycarbonate panels for constructions - roofs (transparent preferred - mine was on sale and it is light brown)
-wood to build the wooden frame
-wood paint
-network cable 20 meters (UTP cable)
-sanitary silicone 2 tubes 
-hot glue sticks 4-5 sticks
-thick paper pattern to align the segments and the digits - 6-8 A4 sheets (2 types - small and big)
-transparent packing tape
-plastic crosses for ceramic tiles 100 pieces pack should be more then enough (the thickness matter, so 3-4mm is ok or use 2, each one on top of the other)
-others (?!)

Unfortunately at the moment of building this huge 7 segments 8 digits LED display I didn't take too many pictures, I had no intention to share that experiment, but now I realized that it may be interesting for others as well.
Due to this reason, the instructable did not documented with pictures each detail, some of the existing pictures are not the best or the most explicit, so you need to understand my English or to imagine another way of performing the same operation. Or simply to ask where you don't understand :) !

Let's start!
2012/12/10 Edit: LED stripes -> LED strips - see comments for more explanations
azurechnica15 days ago

Would you say your display is visibile outdoor during the day? For eg. at a football ground.

nikhil_ms1 month ago
Can you suggest an alternative for the npn pnp transistor pair which is connected to the common anode pin of the segment.
Can i use a pnp Darlington pair transistor to do this or any ic. Because in my design i need 8 similar transistor pair circuits. If i use this circuit i need 16 transistors and 24 resistors to do this, which consumes more pcb space.

Please help.
CatalinRO (author)  nikhil_ms1 month ago

Which PNP/NPN pair are you referring to? The application requests to control each anode and each cathode (upper and lower sides), for the upper side you need to drive the P channel using the NPN transistor. Try to use dual transistors or transistor arrays if you encounter real estate constrains (e.g. IRF7307, ULN2004 etc)

How can i use it as a count down timer with a microcontroller ?

Neat, you can easily build this as a wireless display. Just add a bluetooth module to your microcontroller.
jeffer882 years ago
nice, and you have the schematic for the connection with a microcontroller?
stage power  or use of transistors?
CatalinRO (author)  jeffer882 years ago
You need transistors because a microcontroller is too weak to drive such load and also the load is at 12Vdc (micronctrollers usually need 3.3 - 5 Vdc). You need a P channel MOSFET to connect the +12Vdc to the LED segment and an N-channel MOSFET to connect the GND to the LED segment. The N-channel can be driven directly from the microcontroller, but for the P-channel you need to use an NPN transistor to drive it. Later on this year I'll come back with a nice instructable about this topic.
Please, when do you suppose to post instructable about controller? Please please
CatalinRO (author)  Lukas_CZ1 year ago
Initially I started to make this project with a concrete purpose, but after a while the purpose disappear :). What I can tell you is that the electronics for controlling the LEDs is pretty simple and I tested it, I can share that schematic. What I really don't have and someone should try is to program an Arduino for instance and to check my assumptions, instead my huge display, simple small 7 digits displays can be used. Does it make sense?
This is a well done project.
Not sure what I would use it for, but the LED strips are a great way to overcome the huge wiring issue that accompanies a Seven Segment Display.

How about a Debt Clock. Don't know how you would drive the display but it would turn heads. 14 digits unless you wanted to enumerate cents too. Then you would need 16 digits.

Great Job!
CatalinRO (author)  burningsuntech2 years ago
A Debt Clock? I want something more optimistic :)
Driving the LEDs is pretty straight forward: for this setup (7 segments and 8 digits) I have a bus of 7 lines for each segment and another bus of 8 lines for each digit, each of these lines is controlled by a microcontroller pin (15 pins in total) and using multiplexing, the result is displayed.
Due to the fact that the LEDs are powered at 12Vdc, I cannot drive them directly from the microcontroller pin, so I need to drive them through an external transistor. Basically I need to separate the positive supply from the anode of the LED strip and the ground from the cathode of the LED strip, this is done using a P channel MOSFET and an N channel MOSFET. I tested on a breadboard the configuration and it worked - check the attached schematic, if I apply logical 1 (5Vdc) on both transistor inputs, the LED strip is glowing, if one command is 0 logic (0Vdc or ground), the LED strip is off. My digits bus is the anode (+12Vdc), my segments bus is the cathode (ground or GND / 0Vdc).
Manny B2 years ago
Wow. That is GREAT! Kudos to you fine sir or madam.
tristantech2 years ago
I love big LED projects! Nice work. I have been planning on making a similar one (with alphanumeric characters) for a while now. This is a good inspiration
CatalinRO (author)  tristantech2 years ago
Hmm.... that is something more interesting to be seen than my display. I'm looking forward to see that one. More LED strips (you need 16 LED segments per digit), more work, more wire, but more info to display => just better! Good luck! :)
It would be a challenge and tons of work to get all of those LEDs installed. I really like how you used the tape instead of mounting discrete LEDs and soldering them all by hand.
CatalinRO (author)  tristantech2 years ago
Initially was the idea of having some kind of display to count the time at a local cross-country mountain biking contest, LEDs were the choice, but I was not happy about soldering so many LEDs, I had doubts about the feasibility and so on. Therefore I came to the conclusion that LED strips can make it possible, I tested the concept and I built the display, but in spite of all my efforts, I didn't succeed the microcontroller command in time, only the display. But that is another story for another instructable :)
jingobd2 years ago
My friend asked how to make it.. Now im going to ref. this tuto to him.
Mr_Anderson2 years ago

Nice One!
CorriePover2 years ago
Hello You
I think what plan back Rounding times If that's annual New year 2013 for completion time walking 10,9,8,7,6,5,4,3,2,1, 12 hours, hurray New year
Therefore I want new building with large plate members gezoekte lighting.
I would like to build something, I know not on Electronic print
I hope that with your answer?
With friendly greetings; Corrie Pover
CatalinRO (author)  CorriePover2 years ago
Yes, it can be used as well to countdown the last seconds of 2012 :) 10,9,8,7,6,5,4,3,2,1 -> 2013 Hurray A happy new year 2013 :)
You can build such a device but you need an electronic board to command the LEDs to display the message. Search the internet for a count down timer with 7 segments digits and you can start from there.
Hurray :)
jbh1232 years ago
One of the design constraints was "reasonable cost." Were you able to meet that requirement? Are you willing to say how much you spent?
CatalinRO (author)  jbh1232 years ago
Good point! :) I didn't count yet, but let's give it a try:
-LEDs - 2 reels - 60$ both
-polycarb sheet - 20$
-network cable - 5$
-hot melt - 3$
-sanitary silicon - 5$
-screws, plastic crosses, cable ties - 3$
-wooden frame - this is hard to estimate, I think it would cost me around 30$ (someone did it for me and didn't charge me)
-some paint for the wooden frame, hooks and carabiners - 10$
*these prices are here, you may have cheaper stuff in your country.

Did I miss something? If not, ~140$ (136$ to be more precise), so maybe you can say a maximum 150$ for the display panel itself. Of course you can make it cheaper, but even 150$ looks cheap for a 6ft display.
This display is useless without some electronics behind, but that is another story I'm working on (a microcontroller board with buttons, LCD display and power MOSFETs for driving the LEDs).
Johnny 5C2 years ago
Not being picky CatalinRO. Your English is better than mine, and I'm English...

Lots of uses for those LED strips.
CatalinRO (author)  Johnny 5C2 years ago
No, never said anything as a blame, I found Instructables as a chance to improve knowledge as my English as well. but seriously, initially I used strips and later on I did a find and replace to stripes :))) and now I did a more extensive research and I found that it is strips (Kurt E. Clothier explained me pretty well the differences). Anyway, thanks for the notification! :)
Johnny 5C2 years ago
Good job.
Going to look at the polycarb as the base structure for a solar panel after seeing this.
Am I the only one reading stripes, as in what you get in toothpaste?

Strips right?
CatalinRO (author)  Johnny 5C2 years ago
I received a good explanation and I will correct my wording in this instructable, thanks for pointing to that issue! :)
CatalinRO (author)  Johnny 5C2 years ago
Yes, I was thinking that the polycarb is a good base for the solar panel, light and cheap.
Regarding the stripes / strips, sorry, I cannot help you :) aren't the same thing? (English is not my native language). Thanks!
Awesome job. I think if I ever have to make one this big, I will combine your techniques with my own: DIY Large LED Lit 7 Segment Display.

I love using those strip lights when I can - they make it so much easier to do!
CatalinRO (author)  Kurt E. Clothier2 years ago
I just saw a comment about stripes or strips, so are there strips? I mean for me was almost the same term, since English is not my native language. Thanks!
Maybe this will help...

A stripe is usually a pattern, not a tangible thing. A zebra has black and white stripes, and you can paint striped lines. The American flag is composed of 13 stripes.

A strip is a description of an object (tangible or not) that is long and slender. Airplanes take off and land on an airstrip. The famous road with casinos in Las Vegas, Nevada, is called "The Strip." The LEDs in this project come attached to an adhesive strip.

I know English can be a confusing language, and there are many variants: British, American, Australian, etc. The word strip can be used to describe a single stripe, but the opposite is generally not true.
CatalinRO (author)  Kurt E. Clothier2 years ago
Thanks explaining! I have to correct my wording :)
This is fantastic, the polycarb diffuser really makes it work. Definitely going to be on my to build list.
CatalinRO (author)  Edwardswolentoe2 years ago
I wish I would have the chance to try more polycarb colors before making a final decision, but I was in a rush. So if you build this and you have the possibility, it worth give it a try, please let us know the result :) Thanks!