Hey guys

I'm currently brainstorming on how to build a circuit for a school project. Basically we've built a model city on a huge board. Let's say as big as an average chalkboard or whiteboard in school.
The board is filled with a two rows of LED's, so that's a huge number of LED's. The gist of our experiment is that when someone types in a certain number let's say 1234, the LED's light up. So if 1234 is written LED's will light up low. However if 5678 is typed then the LED's shine bright. Basically there are only gonna be like 3 or 4 number combinations that are going to be allowed to type in. So dim, medium, bright and very bright.
Any ideas how this can be accomplished?
I was recommended to use a microprocessor? Any recommendations which one? Cost efficiency is something I am considering.
So if I use a microprocessor will I still have to use a laptop for someone to type the numbers in from?

 

You don't want microprocessor. What you want is microcontroller, commonly abbreviated uC.

As far as led brightness. A more sophisticated approach would be: off, dim, bright, or bight and very bright. The bright and very bright might be possible or might not be.

If you don't use computer to input number, you will need a circuit for input, a simple keypad for example.

So. So far you will need (if you do it without computer):
* microcontroller (uC)
* led driver circuit connected to uC (you may need three/four of them, one for each brightness)
* keypad connected to uC (to input number to select brightness)
* lcd display connected to uC (to display user input so that user knows which brightness was selected)

 

I'll start with a bit of a quibble. "huge board" "filled with 2 rows of LEDs" "so that's a huge number of LEDs". We need you to clarify that because there are no 2 rows of LEDs that will fill up 3 or 4 feet of board.

Now, it seems you want to make up 3 or 4 input sequences that will cause a change. Is that most of the educational part of the project? I mean, there are some really simple ways to do this, as opposed to decoding ASCII characters or 10 digit keypad inputs.

Microcontrollers are dead cheap, but you need to bake this idea a little more. Probably waiting for a bit of education on how complicated each method gets, right?

I didn't say anything about changing the brightness of LEDs because that's trivial.

Remember, this is a conversation. Your turn.

Edit: Please go to "User CP" and type in your location so we can find parts for you if we need to.

 

I think I understand the project a little differently. My understanding is that you have built this model city on a huge board, and there are some LEDs on the board, and you want to control all the LEDs at the same time. At any one time, all the LEDs should be in one of five states: (1) all the LEDs off, (2) all the LEDs on dim, (3) all the LEDs on medium, (4) all the LEDs on bright, and (5) all the LEDs on very bright.

Is that correct?
How many LEDs are there?
Are the LEDs all the same?
What is the model number of the LEDs?
Better yet, what is the color, forward voltage, and maximum current rating of one of the LEDs?
What is your power source (voltage and current) for lighting the LEDs?

That may seem like a lot of questions, but the answers will ensure that you get good help here.

 

Yep that's it!
I want to control the LED brightness at the same time.

I have access to our Lab whenever I want and I know we have Arduino microcontrollers but we probably have other types too. I was wondering if I could maybe do the project on a small scale and then build it on the board.

Is their like a prototype I should build on a breadboard and then ask you guys further. My main concern is what are the numbers going to be inputted into and then how are all of the LED's going to be connected to the main controller.

I'm not in the lab right now that I can tell you the LED properties, I will probably go there in an hour. But any prototype suggestions are welcomed.

 

The voltage of the LED is important. Too much voltage and they overdraw current rapidly and poof! Bright ones can be up over 3 volts, but red or yellow may only handle 1.5 volts.

Are they wired up yet? If so, how are they wired to each other?

 

So we have the 2-2.4V of red LED's. We have multi colors of the standard LED packets. They are not connected. This is the first phase of the project.
I'm browsing through ideas of how I can connect like 20 LED's series/parallel and control their brightness with a micro-controller.
Another thing confusing me is that I am not building this on a breadboard so how are they going to be connected.
any suggestions are highly appreciated

 

So I need to decide:
1) What the user will enter the combination of numbers in.
2) How the combination of numbers will be received by the LED's so they understand what level of brightness they need to shine on.
3) How the LED's are connected to each other

 

If you would answer some of the questions you have been asked, you might get better help.

Bob

 

Okay here are the answers:
1) Approx. 20 LED's
2) Yes all the LED's are the same
3) COM-00533 is the model number of LED's
4) Red, 1.8-2.2 VDC forward drop, max current 20mA
5) Power source is yet to be decided

 

That's better.

Depending on the voltage of the power supply, you would connect some number of LEDs in series with a current limiting resitor. Mutiples of these series connected strings would be connected to the power source in parallel.

When you know the voltage of the power supply, we can give more details about the number of LEDs in series and the resistors.


Bob

 

But I am not building this on a breadboard so how are they going to be connected in series and parallel?

 

So I have E3647A which can provide voltage from 0-35V

 

Edit: Please go to "User CP" and type in your location so we can find parts for you if we need to.

Maybe the user name is a clue?
Max.

 

My location is in the U.S

 

If I were doing this, first measure Vf of each LED & put them in piles separartd by 1/10's V per pile. Ballance highs & lows so that you have 2 = strings. Assuming that at 20 mA there is a 20 V drop / string. Add a 200 Ω resistor for each string, tie strings in parallel, & crank up power supply to 24 V. If you want to try it out before mounting to city board, & assuming LEDs have leads, solder tips of leads together, add resistor & tape to a sheet of cardboard. When moving to new position , just cut off the tips, keeping the strings seperate. Use PWM for brightness control. Note the duty cycle that gives desired brightness steps. You may not see much difference between 80% & 100 %. A single transistor or FET can interface μC to LEDs.

 

As for the wiring I guess I can connect the LED's through wiring them together in wither series or parallel
So the main question for me is
1) How to enter a number combination
2) How the LED's understand which brightness level to get to by the numbers inputted

Also which microprocessor do you recommend?

 

Many microprocessors include PWM

 

But I am not building this on a breadboard so how are they going to be connected in series and parallel?

With wires?

Bob

 

As for the wiring I guess I can connect the LED's through wiring them together in wither series or parallel
So the main question for me is
1) How to enter a number combination
2) How the LED's understand which brightness level to get to by the numbers inputted

Also which microprocessor do you recommend?

From these questions, you have a lot more to worry about than how to connect your LEDs.

It sounds like you have no experience with microcontrollers. You have a lot to learn.

Bob