Giant seven segment displays

Color distortion

As part of the China trip last week, we had a little scavenger hunt, where the challenge was to build something with parts and tools acquired at the electronics markets.

Here's what I found: a single-digit seven-segment LED display with twelve inch digit height. (Whoa!)

In the cabinet datasheet

When I came across this display, it was in the display case of a vendor at the SEG electronic market-- it was too tall for the display area so they had to put it in sideways, next to the 8" displays. (It's the one with the green protective film.)

I'm guessing that they don't sell too many of these because they didn't have a datasheet handy. They showed me some similar displays in their catalog, indicating how each segment is wired up, and somehow communicated to me that the internal wiring of the 12" digit segments had 15 x 4 LEDs: four LEDs in series, fifteen times in parallel. While that would be nice-- meaning that it could be run off of about 9 V DC, it seemed a little improbable, based on what I know about big LED displays. So, I shopped around and got both a 12 V power supply and a 24 V power supply, just in case.


Off, safe!

Each segment of the display is an independent piece of molded plastic, on a huge but inexpensive circuit board. The circuit board is mainly just a mechanical fixture to hold the segments in the right places.


Driving a segment Transistors

WIthin each segment is indeed a 15x4 array of superbright red LEDs, but it turned out to be 15 in series by 4 in parallel. It runs okay at 100 mA, which takes about 21 V across the LED part. (Good thing that I picked up that 24 V power supply.)

My driver circuit is shown above on the left-- an AVR microcontroller just turns on the transistor to drive the segment. On the right, a photo of the seven transistors on a little protoboard. I put it all together with a $3 soldering iron.

Tom Igoe (or possibly someone borrowing his camera) managed to take several good photos as we all worked together building things late at night in a bar at the hotel.


ATmega

Here's the microcontroller part of the setup. I used one of our target boards to just drive the seven transistors as GPIO outputs. The ATmega168 was purchased locally. There's nothing on this board except for the microcontroller, the programming header, and the wires to the transistor drivers. Power was provided by USB, through my USBtinyISP.

(Note: the scavenger hunt rules were a bit nebulous, but it had been agreed upon that everyone was allowed access to Arduino-class development tools.)


Color distortion

And it's almost painfully bright. You can see the wall being lit up by the pure red glare, while the segments themselves,also pure red, only give washed out colors on a digital camera. Not a problem: you can always turn brightness down. :)


Embedded video #1: A "hello world" demo put together in the hotel room in Shehzhen:


Embedded video #2: A demo put together back home in California: A single-digit clock.

There's some interesting potential here. (Of course, maybe six in a row would look better).


Finally (since people are asking us already-- before we've written this up!) it looks like we'll be getting some of these for our web store. Woo!

18 comments

The following comments are owned by whomever posted them. This site is not responsible for what they say.
Authored by: Anonymous on Wednesday, March 04 2009 @ 09:58 AM PST Giant seven segment displays
Cool. Bigger always is better. ;-)

And, I like the serial digital clock. However, I'm still waiting for someone to implement a one bit clock, where the time is sent by flashing the single LED the appropriate number of times (e.g., 12:47 would be blink blink-blink blink-blink-blink-blink blink-blink-blink-blink-blink-blink-blink). Unfortunately, as near-sighted as I am, I wouldn't even be able to read a 12 inch clock without my glasses from much more than a few feet away (Yes, I'm THAT near-sighted.).

Dave
Authored by: Windell on Wednesday, March 04 2009 @ 03:22 PM PST Giant seven segment displays
Well, we're getting 20-inch displays next, so maybe that would be better?

---
Windell H. Oskay
drwho(at)evilmadscientist.com
http://www.evilmadscientist.com/
Authored by: Anonymous on Wednesday, March 04 2009 @ 02:10 PM PST Giant seven segment displays
I bet the Spark Fun guys wish they knew about these a few years ago!

http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=47
Authored by: Windell on Wednesday, March 04 2009 @ 02:53 PM PST Giant seven segment displays
Nathan from Sparkfun was one of the people in our group. Didn't look like he had anything to regret about that project!

---
Windell H. Oskay
drwho(at)evilmadscientist.com
http://www.evilmadscientist.com/

Authored by: erik on Thursday, March 05 2009 @ 05:01 PM PST Giant seven segment displays
Hi guys,

I love this site!

I live in Shenzhen, so if you need help getting more of those 12 inch digits (or anything else) just let me know.

I go to Hua Qiang Bei (the electronics market in Shenzhen) all the time to drool over all the gizmos and components for gizmos.

Cheers

Erik
Authored by: davidhaile on Thursday, September 24 2009 @ 06:35 AM PDT Giant seven segment displays
Erik,

Do you have a source for extremely large 7-segment displays? 12" is good! 15" even better. If they aren't too expensive, I'd buy 100 at a time.

David Haile
Fort Collins, CO USA
haile dot david at gmail dot com
Authored by: Anonymous on Thursday, February 25 2010 @ 01:28 PM PST Giant seven segment displays
Hi Erik.

Thanks for your offer. Have you seen any 15" or 16" displays similar to this one? That would be the ideal size for my application.

Thanks ....... =PR=
Authored by: Anonymous on Friday, March 06 2009 @ 09:32 AM PST Giant seven segment displays
As I am severely nearsighted, I could use these to build a clock I can actually see from my bed with my glasses off. Of course, it would be so bright we'd never actually be able to get to sleep, unless I drove the things at extremely low power.

(And there's also the little matter of it costing over $300... not sure my wife would be too keen on that.)
Authored by: Anonymous on Saturday, April 18 2009 @ 10:52 AM PDT Giant seven segment displays
I too could do with a clock with digits that size. At the moment I sleep about a foot from a standard size LED clock and I can still barely make out the time when I wake in the night! Though I also may struggle if the price tag is $300.
Martin
Authored by: Anonymous on Tuesday, June 30 2009 @ 05:44 AM PDT $300 ?!
I don't get it. Why would something like this cost $300 ?

~ Matt,
Authored by: Anonymous on Tuesday, September 08 2009 @ 02:00 PM PDT $300 ?!
May be because it would take at least four of them?

One solution to clock-is-too-bright is the computer with voice-activated response. My old iMac running OS 9 with monitor off will reply to voice command "Computer, what time is it?" with the audio response.

Another is 16 10mm LED's mounted into a plastic pipe, displaying the time in BCD. mine alternates between 4-digit year, 2-digit month + day of month, and 2-digit hour + minutes.

Any larger, and those 7-segment displays can be read from space. They probably already can be seen from space.
Authored by: Anonymous on Tuesday, September 08 2009 @ 02:18 AM PDT flow chart
could you show or help us in creating the flow chart of the count down clock or give us any example and we will further modifier similer thing here is my E-Mail Lwandle2@webmail.co.za
Authored by: Anonymous on Friday, October 23 2009 @ 09:34 AM PDT Giant seven segment displays
hi
i would like to know where u bought ur display from
Authored by: GoatRider on Friday, February 26 2010 @ 11:47 AM PST Giant seven segment displays
From the article:

He found them in China, and now sells them in his web store.
Authored by: GoatRider on Friday, February 26 2010 @ 11:49 AM PST Giant seven segment displays
Hmm, odd, it gets an error if I include a link to the web store in my comment. Anyways, the link is in the last sentence of the article.
Authored by: Windell on Friday, February 26 2010 @ 12:00 PM PST Giant seven segment displays
I'm very sorry about that error- I reported it yesterday and the developers of our CMS (glfusion) have just sent me a new library that should fix it. Fingers crossed.

---
Windell H. Oskay
drwho(at)evilmadscientist.com
http://www.evilmadscientist.com/
Authored by: Anonymous on Wednesday, March 10 2010 @ 12:22 PM PST Giant seven segment displays
Hello!

Can you provide additional information on how to controll it?
Authored by: Windell on Wednesday, March 10 2010 @ 12:32 PM PST Giant seven segment displays
I'm not sure what you're asking... we explained how we controlled it in this article.

---
Windell H. Oskay
drwho(at)evilmadscientist.com
http://www.evilmadscientist.com/
Welcome to Evil Mad Scientist Laboratories. New projects are posted on most Wednesdays.


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