Neat project I was asked to do

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This will be my first real AVR project and I'm pretty excited to start it. Just need some suggestions first.

My church asked me to make a sign or display that they can put up on a wall. The sign will display a number that can be programmed via keypad or something that will turn on at request. The idea is to secure the nursery and children's school. They are making a new policy where you are assigned a token when you drop your child off that signifies you are their parent. When you pick up your child you need to present the token to teacher. This is the same sort of thing they do at birthday party events.

The deal for the sign is when a child is acting up, the teacher can punch in a number and it would be displayed on a wall. Then the parents can see the number and come check on the kid. I was thinking 2 big 7-segment displays and a keypad interfaced to an AVR. Maybe a "clear" and a "set" button on the device to erase the numbers on the big display. I am not sure if they make large 7-segment displays..maybe there is some sort of dual digit LED sign I can use instead. Thanks for any feedback.

Chief Tinkerer

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How big do you want to make the wall-display ? Can you provide specific dimensions ?

How far from the control keyboard is the position of the display ?

I do not know how much is the budget of your project, but a "cooler" security method is to display the picture of the child with his guardian in a big tv display, instead of displaying a number in correspondence to a specific child.

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I agree..that would be a lot cooler, but the cost difference from a picture display to a LED display would be quite big (I would think). The sign is about 40 feet away from the keyboard. I was thinking about using CAT5 cable to carry the signal and some sort of buffer/driver to amplify it from the control unit to the sign.

Each number on the wall should be big enough to see from 75 feet away. I was thinking maybe 1 foot high and 6 inches wide.

Chief Tinkerer

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Here is a pretty big led display for some inspiration.
CLICK ON LINK

I was playing around with using some 6" ccfl to make a 7 segment display, and that might be an alternative. But I think some super bright leds would be better.

You might also consider being able to display multiple number to notify multiply parents. Maybe just cycle them.
A scrolling alpha numeric (ledmatrix) sign would be more flexible, but a somewhat more complex design.

-carl

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I was just at our local driver license office. Its the sort of place where you take a number when you go in and there is a number display on the wall.

In this display, the numbers were about 8" x 6" and in a 7-segment arrangement. But the segments were made of standard (probably high brightness T-1 1/4 or larger) LEDs. They were easy to see in normal room brightmess/ There were several displays.

Once you make one, a second is easy and you link them all to a single keyboard device with RS422 or such. The keyboard outputs the number to be displayed (or no number). This way, you can have as many displays as you want. CAT5 would be a good choice.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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Quote:
...a second is easy and you link them all to a single keyboard device...

...might also consider being able to display multiple number...


If you make them addressable in some minor way (4 position DIP switch, for example) you would have the option of expanding the system by hanging more than one on a single wire and displaying the same, or different, numbers on each.

Chuck Baird

"I wish I were dumber so I could be more certain about my opinions. It looks fun." -- Scott Adams

http://www.cbaird.org

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Quote:
when a child is acting up, the teacher can punch in a number and it would be displayed on a wall.
666 ? :lol:

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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If you want to avoid running wires in the building, you might consider an IR or RF link. Since this is you 1st project you'd be wise to get it "working" using a wire link, then perhaps upgrade with IR or RF. You can easily go 75 ft with high power LEDS. I worked on one that would go several hundred feet outdoors in direct summer sunlight.

You can probably "make" your own digits using perfboard & a bunch of leds strategically placed. There will be plenty of room to install your processor. Then put it all in a nice box with some red plastic on the front.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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Quote:
...you might consider an IR or RF link...

X10 (power line zero crossing) would be another easy way to go for such low bandwidth. There are schematics for lots of MCU-X10 projects floating around.

edit: Google has 99,900 hits for X10 AVR.

Chuck Baird

"I wish I were dumber so I could be more certain about my opinions. It looks fun." -- Scott Adams

http://www.cbaird.org

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H. Carl Ott wrote:
Here is a pretty big led display for some inspiration.
CLICK ON LINK

I was playing around with using some 6" ccfl to make a 7 segment display, and that might be an alternative. But I think some super bright leds would be better.

You might also consider being able to display multiple number to notify multiply parents. Maybe just cycle them.
A scrolling alpha numeric (ledmatrix) sign would be more flexible, but a somewhat more complex design.

-carl

Now that is a pretty badass clock I must admit. I think I'll go for something like this using some superbright LED's. The project will defenitely be done with wires at first as wireless is out of my range of knowledge at the moment. Does anyone know where to get LED light bars like he uses? I will let you guys know how it goes.

Chief Tinkerer

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Two 7" high 7 segment led displays cost nearly as much as a cheap 17" LCD monitor. So, unfortunately, A scrap PC with a new LCD panel would be a faster and cheaper way to do this...

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triden wrote:

Each number on the wall should be big enough to see from 75 feet away. I was thinking maybe 1 foot high and 6 inches wide.

If you can construct manually the large digits of the wall display then your plan is valid, or else the cost of that big digits is very-very big one! Especially if you plan to place the display in a bright hall. Then, you need a very bright display also.

I suggest to consider the following alternative:

Use a TV set with a VGA compatible input, with the appropriate brightness and size.

Drive the VGA signal with this mini board http://www.dontronics-shop.com/p... combined with http://www.dontronics-shop.com/p... (or with similar products)

You can control the mini VGA circuits with a simple controller, and you can draw on the TV screen whatever you want.

When your system does not use the TV set, it can be used for other purposes accordingly, with infrared control from your keyboard-controller.

This way, you can also achieve a low budget solution.

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triden wrote:
H. Carl Ott wrote:
Here is a pretty big led display for some inspiration.
CLICK ON LINK
-carl

Does anyone know where to get LED light bars like he uses? I will let you guys know how it goes.

Sparkfun sells those light bars, you just have to look around their site. Not really cheap. I'd be tempted to just get a pile of high efficiency red leds and make a modular pcb, and use them to build up to a 7 segment display.

I also like lpapad's idea. It's certainly more flexible. And if you have a spare lcd laying around, pretty cheap too.

You could also go this route,
Pick up something like tis on ebay:
http://tinyurl.com/yhjcq9
And start hacking away.

-carl

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While a video monitor might wind up being cheaper, the LED sign has the advantage of being "dead" when no number is displayed. It seems more descrete, a requirement when this is set up in a church. A photo popping up on the monitor would definitely attract unwanted attention.

We have such a system (two digits so no 666 possible). It works well as long as the parents think to look at the display when it flashes on. Few people who don't have a child in the nursery pay attention to it. I'm pretty sure it is a commercial product.

Besides summoning parents, our display has been used (on rare occasion) to flash ball game scores, though never during the sermon - the pastor is cool, but likes no competition.

"It's easier to ask forgiveness than it is to get permission" - Admiral "Amazing" Grace Hopper.

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My church used a system exactly like what you're describing for years. We just recently (last Oct) moved into a new facility and now they hand out pagers to the parents (kind of like what you get when you're waiting for a table at a resturant). The signs (one on each side wall) looked like they had standard LEDs arranged like a 7-seg display (maybe 3 or 4 LEDS per segment). They were also housed in wooden cabinets so it's possible they were custom built, I don't know (before my time). I don't have any details as to how they were controlled, but this is definitely not a new idea. It's possible they just bought them off the shelf, in which case it may be cheaper than reinventing the wheel.

Before I found out that they were going with the pager system (less intrusive to everyone else) I was thinking of voluteering to design new ones for the new building, oh well. It does sound like a fun project though.

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A couple of years ago I did a similar project to the Sparkfun one, though nowhere nearly as large or as cool. Rather than lightbars, I used individual high-brightness LEDs, mounted to styrene I-beams. These were then arranged in standard 7-segment digits.

These I-beams can be had from any hobby/modeling store - Tower Hobbies online for example. They're perfect for the job. The I-beam width was exactly right for 5mm LEDs, and the I profile hid the wires very nicely. The whole channel of the I-beam glowed, since the LEDs poked through holes in them. They're bright white, so any side-scatter light is reflected all over.

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I forget exactly how many LEDs were used - 6 or 7 in series with a single current limiting resistor per segment, and a 12V power supply. We used an Allegro LED driver - an 8-bit latch. A6821 maybe ? I don't recall exactly, it was a one-off knock-together job on protoboard. It used an 8515 to receive digits (phone numbers, time, scores, etc) via UART and spit them out (scrolled no less !) to the digits. Actually, the scrolling part was easy - the drivers could cascade one to the next, so there was no actual real scrolling code :oops: It just happened/worked.

Dean 94TT
"Life is just one damn thing after another" Elbert Hubbard (1856 - 1915)

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tcouey wrote:
My church used a system exactly like what you're describing for years. We just recently (last Oct) moved into a new facility and now they hand out pagers to the parents (kind of like what you get when you're waiting for a table at a resturant). The signs (one on each side wall) looked like they had standard LEDs arranged like a 7-seg display (maybe 3 or 4 LEDS per segment). They were also housed in wooden cabinets so it's possible they were custom built, I don't know (before my time). I don't have any details as to how they were controlled, but this is definitely not a new idea. It's possible they just bought them off the shelf, in which case it may be cheaper than reinventing the wheel.

Before I found out that they were going with the pager system (less intrusive to everyone else) I was thinking of voluteering to design new ones for the new building, oh well. It does sound like a fun project though.

You wouldn't happen to know what paging terminal they use? I designed a paging terminal several years back. One of the target markets for the 'lite' version was churches.

Writing code is like having sex.... make one little mistake, and you're supporting it for life.

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triden wrote:
I agree..that would be a lot cooler, but the cost difference from a picture display to a LED display would be quite big (I would think). The sign is about 40 feet away from the keyboard. I was thinking about using CAT5 cable to carry the signal and some sort of buffer/driver to amplify it from the control unit to the sign.

Each number on the wall should be big enough to see from 75 feet away. I was thinking maybe 1 foot high and 6 inches wide.

Check this shop with low cost big displays:
http://www.futurlec.com/DisplayB...
http://www.futurlec.com/Single_7...
http://www.futurlec.com/Lg_LED_7...

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Thanks for the insight guys. I ended up ordering some big 5" 7-segment displays from futuerlec.com. They were only $11 each http://www.futurlec.com/LED/7SR5... (I thought it was a bargain). I'll make a little enclosure to hold them on the wall and power them with an ethernet cable.

Right now I am working on the circuit schematic. I am thinking of having the AVR drive two BCD to 7-segment latching decoders and then have them trigger a driver IC to power the displays. The BCD decoder will cut down on the I/O lines needed and some code. This way I can just print 0x01 to PORTB for a 1. Depending on the number going out on the bus, I will latch the decoder so only that display will print that number.

Chief Tinkerer

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Quote:

I am thinking of having the AVR drive two BCD to 7-segment latching decoders and then have them trigger a driver IC to power the displays. The BCD decoder will cut down on the I/O lines needed and some code.

If you really care about reducing i/o lines I'd be tempted to just use a couple of shift registers. A very small amount of code overhead. Gives you flexibility in what gets displayed and might also simplify the board layout.

A buffer or just 14 transistors would give you all the current drive you need.

-carl