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binxalot
11-14-2006, 10:33 PM
I'm looking to build a very simple LED grid of about 24 LED lights in a grid 4x6 which I want to be able to scroll text messages·on from left to right.· Like a BETA BRITE but I'm looking to make it bigger than a beta brite and I want it to be mobile.·

Should I look into purchasing a BASIC stamp +·programming board·to accomplish this?· Is that the best route to go in order to make something like this?·I'm starting completely from scratch here as I've never programmed anything like this before, but I figured it would be a neat project to learn and I· can reuse the finished product at work.·

Any ideas?

-Binx

Bill Chennault
11-14-2006, 10:53 PM
Binx--

Like you, I am a novice, as well. However, unlike you, I have some stuff from Parallax and my LEDs are blinking! It is marvelous! :)

The Stamp comes in several flavors, most of which have 16 I/O pins that will allow you to control--often with additional circuitry--things like LEDs and relays and motors. HOWEVER, you mentioned 24 LEDs. You will have to determine how much current they draw and how many will be on at the same time and compare that to the ability of the STAMP to support directly. But, that is not what I wanted to mention: Specifically, take a look at the BS2p40 and the "Professional Development" board. The BS2p40 has not 16 I/O pins, but 32, which sounds much more ameniable to your ultimate goal.

Speaking of your ultimate goal, if you are starting anywhere near my level, you will want to begin with a BS2 (I chose the BS2p24) and the "Board of Education" Rev. C., along with "What's a Microcontroller", all available from Parallax (http://www.parallax.com/index.asp). You will learn a tremendous amount, including how to make multiple LEDs blink . . . including the very simple additional circuitry (supplied) you will need.

--Bill

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You are what you write.

Franklin
11-15-2006, 04:52 AM
The board you referenced seems to have MANY more than 24 LEDS (several hundred) Each letter on that board is 56 LEDS.

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- Stephen

Tommy Bot
11-15-2006, 06:08 AM
The betabrite has 700 (7x100 array) RGB LEDS, each one able to light up as one of 64 different colors.

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(Frequently heard from other's)

Tommy, I know it wasn't designed to·x, but can you make it·do x·anyway?

·

binxalot
11-15-2006, 06:30 AM
The beta brite isn't what I'm looking for here. I want something I can lay across the entire back winshield of a ford explorer that can display messages scrolling across the back winshield.

I've spend the majority of today researching what I need to do and this is what I've got so far:

I need to make two 5x7 LED matrix arrays.
I need to get 2 7414 Hex inverter ICS
I need a PIC to program the inverter to show different letters in the grid and scroll them
other misc parts are resistors, caps and a power tranformer

Franklin
11-15-2006, 10:14 AM
5X7 is just enough dots for one letter. how well will your scrolling look with only two letters?

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- Stephen

latigerlilly
11-15-2006, 03:59 PM
Yes,

You can control all the LED's with just one (yes ONE) I/O pin. Here's how... look at the following schematic:
http://i15.photobucket.com/albums/a371/MINGMAY/Multilight.gif
You can have one coil (I just used multiple coils for ease of illustration) connect to different capacitor & LED combinations. A different value capacitor is used to optimize for each unique frequency. Therefore, using the FREQOUT command, you can control almost an infinite number of LED's using different frequencies. For example, in the schematic I posted here, a 1000 Hz tone will light the LED attached to the 3 uF capacitor, 2000 Hz will light the LED attached to the 0.758 uF capacitor, and 3000 Hz will light the LED attached to the 0.337 uF capacitor.

To figure out the capacitance necessary given a particular mH coil and frequency, use the following calculator:
www.opamplabs.com/cfl.htm (http://www.opamplabs.com/cfl.htm)

To calculate how to make your coil, use this calculator:
web.telia.com/~u85920178/begin/calc-00.htm (http://web.telia.com/~u85920178/begin/calc-00.htm)

A 8.352 mH coil is 6 inches in diameter, 20 winds each layer, and 1.5 inch thick. It is made of 12 gauge solid copper wire.

Here's the shameless plug... PLEASE (please, please) return the favor by answering my questions.
I just need a thumbs up (it will work) or thumbs down (it won't work, here's an alternate schematic) for this:
http://forums.parallax.com/showthread.php?p=615389

I just need a part number for a DPDT relay for the following schematic:
http://forums.parallax.com/showthread.php?p=615420

Thank you and God bless,
Lilly.

Post Edited (latigerlilly) : 11/15/2006 11:02:50 AM GMT

Bean
11-16-2006, 09:33 AM
Binx,
· Most displays of this type are multiplexed. Google for "multiplex led display".
· Basically you need one pin for each column and one pin for each row.
· So for a 5x7 matrix you need 12 pins.
· For a 10x7 matrix you need 17 pins.
· There are also ICs that will do the multiplexing for you.
· You'll need at least 4 characters if you want the display to be readable while scrolling.


Bean.

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Cheap used 4-digit LED display with driver IC·www.hc4led.com (http://www.hc4led.com)

Low power SD Data Logger www.sddatalogger.com (http://www.sddatalogger.com)
SX-Video Display Modules www.sxvm.com (http://www.sxvm.com)

"People who are willing to trade their freedom for·security deserve neither and will lose both." Benjamin Franklin
·

Zoot
11-16-2006, 09:46 AM
I'll echo Bean's comments and strongly suggest getting an LED driver IC which will take care of the multiplexing/scanning of the LEDs for you. Since many LED driver chips can be cascaded, the pin count on your Stamp will not be an issue (for example the MAX8221/8219 only needs 3 pins -- data, clock, load/chip select). Each MAX8221 can drive 64 LEDs and they can be cascaded together. That's just one example because is there is a lot of code for that chip floating around the forums.

Another advantage to a driver is that you generally only need one resistor to set the current for ALL the LEDs, plus you get features like being able to set brightness with your code "on the fly".

There are other driver chips that will handle many more LEDs, as well as the ability to set colors on 3 and 4 pin LEDs, but they get pricer (MAX82xx chips can be had for $10-$20 each).

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When the going gets weird, the weird turn pro. -- HST

Post Edited (Zoot) : 11/16/2006 1:50:41 AM GMT