Large 8inX10in 7 Segment Displays Netduino Mini Powered

Hello,
So I shoot fireworks for my local town professionally on the 4th of July and for our Winter Wonderland display the Sunday after Thanksgiving. We have a long 45min show filled with ground and aerial displays and we have rounds. Each round has specific display piece's that we shoot with a team of about 8 on the ground team. When the explosives are going off and the adrenalin is pumping though our pyro blood it is easy to lose track of what round we are on. So I was asked if I could come up with a large display this year that would indicate the round we are on for the shooters. what i came up with was a large 8inX10in 7segment Display using a SN74HC595 for each Digit. Since we shoot 12 rounds I needed 2 digits.

For this design I used several different construction materials however it took me longer than it should have to build. So I have designed a board that I want to use for next year and replace my low intensity Red Led's with High Intensity Blue LED's. The display only really worked well once the lights went out. I also only had 2 led's per segment where I think three would be better.

Because of this I designed a board for my uses next year. However since it is 8inX10In it is a little pricey to produce only the number I need for my purposes. So I was wondering how may people would be interested in a kit to build your own clock or large 7segment displays with netduino drivers. Since I am part owner and president of a electronics design and distribution company it seemed Ideal that I make this into to kit we can sell. However the kit would likely be in the range of $40 for just 4 7segment Display boards. it will contain 21 high intensity LED's of your chosen color and instructions on how to build your own large display and drivers for the netduino. I have added a poll to this post. Also Each board has it's own 5V regulator with power direct from the 6-12VDC Power source provided throughout the displays. This resolves other issues encountered with the fast 2 day build with supplies on hand. For instance when both displays were showing 8 the available power dropped off dramatically and was noticeably in the intensity of the LED's.

Below is a potential Candidate for the production Board. I will follow up this post with pictures of my quick display.

Hi Terry.
The idea is pretty nice indeed, but...
If you were proposing that display 2-3 months ago, probably you could have count on me. We had a village festival and we need such a large display for show the queue counter for serving the dinner. I solved in a hurry with a lcd frame.
Perhaps I could have need in the future, but no ideas at the moment.

Anyway, I'd point out some perplexities about the circuit...

• IMHO, such a large display deserve more than 3 leds per segment. Why not five, for example?
• It looks that the leds are in parallel, instead of series: that sucks much higher current. Why don't connect them in series?
• Each segment is driven by the HC595, but it cannot sink so much current. Why don't drive the led by a transistor?

Cheers

Hi Terry.
The idea is pretty nice indeed, but...
If you were proposing that display 2-3 months ago, probably you could have count on me. We had a village festival and we need such a large display for show the queue counter for serving the dinner. I solved in a hurry with a lcd frame.
Perhaps I could have need in the future, but no ideas at the moment.

Anyway, I'd point out some perplexities about the circuit...

• IMHO, such a large display deserve more than 3 leds per segment. Why not five, for example?
• It looks that the leds are in parallel, instead of series: that sucks much higher current. Why don't connect them in series?
• Each segment is driven by the HC595, but it cannot sink so much current. Why don't drive the led by a transistor?

Cheers

Thanks Mario
Yea like i said this is a purposed design not the final. I did that one in an hour after getting tired of perf board for my two day project. I was planning on using a transistor for drive. it was more to show what a 7 segment is. The other thing is I use while acrylic as a diffuser and I block the light with a foam template between the acrylic and board. The reason behind parallel and not series. Is 2 reasons series if one led goes the whole segment is out. secondly if a person wanted to go with 2 LED's or just one if they have a high enough intensity they could in parallel not in series not unless they ran wires instead of the led's. I also plan on a resistor for each LED which is not shown in the quick board layout. I however could make it so 5/6 LED's could be used and in my scenario the end user could decide how many he/she wanted.

I forgot the link for the solution I had.
http://highfieldtale...-display-board/

Have you tested the display when in an environment like the mine above?

Okay for the reasons about the design.
I surely approve the idea to use one resistor for each led. That should balance the luminosity of the sibling leds, being not perfectly equals.
Cheers

PS: I didn't add a vote to the poll, because I would vote for "maybe".

Mario, I have not tested it in your Scenario I finished my original prototype with 2 led's per segment 2 days ago and used it last night for the first time. for my use it worked ok I would have preferred higher MCD LED's for mine but Mine were pretty low. here is a pic of mine after I finished my first segment. I will post more pics later this evening of the finished prototype. http://dl.dropbox.co...68/_MG_6155.JPG