I found an 8 x 40 LED array at a surplus store online and thought I'd see what I could make it do. Here's the tale

Display Front:

Display Back:

Turned out to be a fun project.

Rick

WOW
What are the dimensions of the array & cost?

Thanks Jim

Great project Rick, and pretty cool website too!

So where did you find the (surplus) display, do they have a stock of these? Or did you get the only one?

I'm not at home right now, but I'd guess it's size is roughly 2" tall by maybe 10 - 12" long.

The board was on eBay for $15. I bought a second one to double the length. I think minor code mods will get that going. Last check he still had 26 of them left if you search 8x40 LED I think you'll find them.

Thanks for the website compliment. I don't know if ill keep up with it or not. We'll see.

Rick

I'm home now, the display is 11" long x 2-3/8" tall. Here is the link to the display on ebay. It still shows 26 available. I figured at $15 that was a fair price -- esecially now that I have it working.

Rick

Looks like some of you have been busy... I see there are only 22 left now.

One thought I have for this project is to turn it into a clock using the RTC module I've documented here on the forum. I think having it show the time, date, temp.. would be neat. I should have enough pins to allow for the button inputs for setting it... That's a project for another day though.

Rick

Hi
I just bought 4 of them. They will work for my Tractor Pull Sled display for the grand stand area. I think I will set up 2 rows of 2 pannels each. One for the distance pulled and one for the weight pulled.

Will use the 2.4mhz radio link fom the sled to the displays.

Thanks for the info and how to make it work...

Jim

RICK

I tried to download your source code and get an error "not found".

Could you maby add it here on Nerdkits???

Thanks Jim

That's odd, it pops right up for me. It even downloads on my phone so I don't think it's a permission thing. The reason I have it there is because it is 3 files in a zip, the font file, the program file, and the makefile. If you highlight the link, what does it say it is linking to?

Rick

Rick

Downloaded fine this time.

Our internet was down for about 4 hours..

Thanks again will post more after I get the boards.

Jim

Ok, Glad you got it.

Rick

Well, got a second display today. Updated the post with the info for the 8 x 80. These displays make it pretty simple. I'm thinking about an enclosure now ...

WOW AGAIN

A second thanks for all your work...

Jim

No problem Jim, I've always had an attraction to the LED Array project here. It was the project that pushed me over the edge to really try to learn basic C programming. I'm far from an expert in C, would consider myself an advanced rookie.

After building my display with the blue Chrismas LED's as documented on the forum here, I had a desire to make the display more than 5 pixels high and longer. The 5 x 5 font just didn't really do it for me. I have played with shift registers for a while so I was pretty familiar with their function. I had also gotten pretty intimate with the code for the LED array. So when this board came along, I figured it could be a marriage of the two, and I knew now was the time to see if I could do with the code what I always wanted to... Make the code work with shift registers. Happily, I was successful.

BTW, I don't know if any more of you have purchased these or not, but if you haven't, and are interested, you may not want to wait. It seems since I have posted about these, 8 have sold - so as of this morning, they are down to 18 left.

Rick

Okay guys, I got 3 coming withint the next week. Once I get these, I'm going to see if I can add this to my rocket launcher project. I think the kids will enjoy seeing the bigger text vs. the LCD text anyhow.

Thanks for all the hard work guys, I really appreciate it!

Kevin / killercow

Are you planning on putting them all three in a row? I'm not sure if there would be enough time in the interrupt to fill 120 bits and leave much time for anything else... but I guess we could find out. I know with 80 there was a noticable decrease in speed and I had to change some of my delay's to make it appear smooth.

Rick

Rick I have been meaning to ask the difference in speed between a shift register and an I2C port expander.

It seems as if one could use the port expander in place of the shift register but I wonder about the speed.

You did a great breakdown on I2C mcu to mcu timing.

Also chaining mcus (Nerdkit Expanded Array) might help with speed issues.

Ralph

I didn't do an mcu to mcu timing thing, probably Noter. He was the one with all the I2C mcu to mcu stuff. I just did a port expander. As for the shift registers, they are built into the displays I'm talking about in this thread so there is no changing them unless you wanted to toss away their driver circuitry and replace it with your own.

Rick

The shift registers can be much faster than I2C. The max I2C rate on the Atmega is 400khz compared to the max SPI rate of (clock / 2) or about 7Mhz on the standard nerdkit.

Thanks Paul, that is what I suspected but did not have any numbers.

Yeah Rick I was just thinking in general not for your specific array which are very attractive, nice find.

Ralph

Rick, I like spending money at times. That and I wanted to have a spare one just in case. But, I'm willing to try 3 in a row. I haven't seen any e-mails from GA yet......kind of like Christmas in July!

Kevin

GA?? Sorry didn't catch what that references...

Georgia....The state that has peaches and bells. Just looked, there are 12 left now. There were 18 or 16 when I placed my order late last night. I've been looking more at your site, very nicely done.

Duh... I'm sorry, I must have been a little slow on that... Wasn't thinking Georga at all.

As for their inventory, it does seem to be dropping quickly. They had 26 left a few days ago when I started this thread.

Thank you for the compliments on my site. I've tried a couple of times to start a site. I typically end up not having enough time to dedicate to it. Hopefully this time will be different. I like the blog software I'm using and the template I found was very customizable to give it the look I wanted.

I even setup a forum. I set it so I would have to confirm personally every new user (hoping to offset spam users) and all I kept getting was bogus users from African and European servers. So I made registration there require human input. I really don't know if it will take off at all though since there isn't anything there to talk about.

Anyway, Let me know how it works out when you get them.

Rick

I ordered two yesterday.

They will probable just set around for a while before I come up with a project for them but I thought they were really neat plus now we have a direct discussion forum we should be able to expand some great ideas of application.

See you there.

Ralph

RICK

I got the 4 displays today. Very nice units. My use will be to display steady info but will update live via radio link. I will not use the scroll feature...

Jim

Cool, post your progress. Right now the code only displays pre-programmed messages. It will be interesting to see an outside datastream.

Rick

I got my 3 boards today. Playing Playstation with my great-nephew now. I'll try to post something after we're done.

I just got mine also.

I need lots of help with these, but I will have to find the time first.

Ralph

I'm thinking about getting a couple more and using a couple 3-8 decoders cascaded - through an inverter so I have enough I/O for the 16 rows. I've already ordered the decoders and inverters and will be posting a 16 x 40 once I get that in. From there if I decide to go to 16 x 80 the code wouldn't require much change.

I don't know why but I just love the marquee projects.

Rick

Incase you get the 16x40 to work I just ordered 4 more of the boards. A 16x40 should allow for a taller & larger readout. Perfect for static display.

If not I will have spare boards for my regular display.

Thanks again for your super work & ideas..

Jim

Apparantly their surplus store has much more of these than initially listed. I noticed this morning that their quantity jumped up to 50 units.

Jim one thing to keep in mind. Even a static display is really not static. The display is constantly having each row written to quickly enough that it appears to stay on. So really there isn't much difference in a static Vs. animated display except during the time inbetween display writing, you adjust the array that holds the display variables. The display interrupt simply writes one row of data from the array to the display successively each time it's called. The array is more or less the "display memory" and the interrupt the "refresh circuitry". Thus animation of the display simply becomes a matter of fiddling with the display memory.

Rick

Thanks Rick for the info. I used the term STATIC in error. I should have said I will use a "NON SCHROLL" type display.. Will be neat to see if the 16x40 will give me a larger display.

I am glad he has more of the units. They seem to be super & very reasonable.

Jim

Well, I got my parts for my interface board to try to do the 16x40. Here's a photo of the prototype.

The hardware seems to be working just fine, but it looks as thought the software will require some major tweaking. The software works based on the assumption that the font is the same height as the display. Since my font is only 8 pixels tall (currently) the "blank" space gets filled in with whatever the last pixel was (on or off). You can see a full writeup HERE.

I haven't decided what I'm going to do, but I'm leaning toward adding another parameter to the display routines for a row coordinate. As long as you guys are still interested, I'll keep you updated.

Rick

Thanks for the update. I would not have figured all this out. Am very interested in the 16x40 display. I got the other 4 boards so have 8 on hand now.

I admire your ability to do the fantastic write ups. Very clear and to the point.

Thanks again for your work... Jim

One of my 4 has a dead pixel and another had a bad column. The column was an easy fix (just a bad solder connection) The bad pixel is looking like a bad LED. If so, I may just buy another board for spare parts so I can ensure the LED's match. I noticed he raised the price $3 :(

I offered him $9.00 for the boards. He accepted the offer both times for 4 board each order..

Jim

Hey Rick how do I download your Array code?

I looked on your RS-micros site but did not see a download link!

Ralph

Did you go to rs-micros or rs-micro.com? Anyway, the link is here for the 4 x 40 My site is rs-micro.com. The blog is at http://www.rs-micro.com/wordpress

Rick

The blog says DS8220, but the picture looks like it's DS8820N. Is that right?

I believe the N suffix just designates the PDIP packaged chip. I just didn't include the suffix in my part number. Didn't mean to mislead.

Sorry, wasn't the suffix I was asking about, but the number. 8220 vs 8820

Whoops. Yep, that's a typo. It is a DS8820N. I'll fix that when I get home tonight.

Good catch.

Rick

Another different LED array source: Sure Electronics DC-LE15111. This is 10 blocks of 8x8 two-color LEDs for $12.90, enough for a 40x16 display with red/green/yellow. Doesn't have any controller hardware.

That's the nice thing about the boards I found. Having a built on driver board is great. Another great thing is, if you want, you can easily remove the driver board from the array and just have an 8 x 40 matrix that you can add your own driver to.

Another driver-less array, 16x16 red for $7 here. It seems like a bad design because you'd be stuck with a 1/16 duty cycle, or am I missing something?

Yeah, they'd be a 1/16 duty cycle but depending on how fast you can fill your rows then switch, I'm sure you could get a pretty good refresh rate to make them flicker free to the eye.

But dim, even if you pulse them at their max current rating. There's a diminishing rate of return on brightness with increased current, even if you go to the pulsed max current. And if you do that, e.g. 130mA times 16 is 2 amps to control. Gets yuckier the more I think about it.

However, can't you pulse above max current since the duty cycle isn't 100%? Isn't that how the NK guys get away with it on their LED Array w/o limiting resistors?

30mA would be a typical 100% duty-cycle value. My 130mA number comes from the max pulsed current with 100us pulses at 1kHz, which is what the Nerdkits red LEDs are like (basic kit, I don't know about the LED array kit).