HELP:electronic billboard

Hello Nayr If you are allowed only logic gates, then this is going to be a large project. I mean that there is going to be a lot of circuitry. Are you allowed to use counters, flip-flops and latches? This is doable if you can use counters and latches (e.g. anything from the '74' TTL logic range), but it will involve a lot of circuitry and the message it displays will esentially be hardwired into it. If can use 74 logic, will post design on website

(when I get it running). Robert

You do realize that this is almost cerainly a project assignment for school.

I can't think of any other reason why somebody would attempt to do this discrete logic unless they were trying to enforce combinational and sequential logic design.

Personally, I am getting really tired of reading "Please Send Me" from everybody that want to be handed a design for their homework. When I was in school, I would have been delighted just to have a usenet group to be able to get hints from.

Yes, It's obviously a school project assignment. Just had some time on my hands and thought it sounded like an interesting thing to do. Robert

Yup. Probably not a direct assignment, more like a "choose your own project". No teacher would ask students to do something like this directly. Not only that, but this is going to be expensive.

Mr. Kupal has a couple of options, as I see it. He can go back to his teacher and ask for another project, because this one is gonna be "acres o' digital". One possibility more within the reach of a novice electronics student would be getting one 16-segment alphanumeric LED display, and then scrolling the letters at one per second, with two blanks after the word. Still a bit of '70s digital logic, but very doable, especially if he's allowed a couple of PROMs. And within a student's budget, too.

Second, he can find a copy of Don Lancaster's TV Typewriter Cookbook (Mr. Lancaster will be more than willing to send a copy

) and look for hints as to how to do something like this. I'd figure he's doomed unless he can use an EPROM at least to store the data, then he can probably use a triple counter (one for multiplexing, one for data, and another for data start position) to achieve the scrolling effect. Not easy. There's a good reason why these things didn't exist before microcontrollers.

The third option is to utilize this newsgroup as the OP says -- you do the work, and send him the bill. Ask for cash in advance.

Good luck Chris

Use a mechanical 'paper tape' loop. Columns of 7 LEDs; when the hole in the tape is under the led, it is grounded, and allows current to flow through. Each LED should be connected to the supply through a small resistor, the value of which is dependent on how bright you want the LED to be. Use a little DC motor to turn the tape on a spindle. If you did it properly, you could use the actual LED leads as the contact points. A gearmotor that runs fairly slowly is the best way to turn it, unless you want to get into your own gears or belts.

--
Regards,
  Bob Monsen

We should take care not to make the intellect our god; it has, of
 course, powerful muscles, but no personality.
    Albert Einstein

Or just use the tape itself to do the scrolling. Perforate a tape that's about 3" wide, put it in front of an EL panel or some kind of backlight, and put a "diffuser" on the front that's got like an array of little bumps, like a bee's eye - that'll give the strobing effect.

Cheers! Rich