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RDEjr8
02-08-2007, 01:09 AM
Hello everyone!
Supernewbie to this forum, hopefully this post is in the correct place and is a simple question.

I·have already completed the initial reading and studying of the "what’s a microcontroller student guide" and also have some rusty knowledge of electronics.
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I plan on utilizing a BOE kit and my understanding of the basic programming will
fit for my first project.
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Initially I would like to program the simple timing of the output to flash the LED’s just like lesson 2. No problem.
Problem is: instead of powering a single LED, I want to power independent strings of LED lights. The strings are low power use approx. 2.4 watts and .02 amps. Ea.
I need to power / control at least 4 independent light strings and as my learning curve goes up I would like to expand to 8/ 16/ or even 32 or more independent channels.
As you can tell by now I would like to create a home made lighting controller.
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Once programmed I desire this unit to be self contained and “plug and play” (no further updates unless I change the programming).
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What I would like to do is create a simple “Home Rec Room Bar Sign” that has the ability to flash 4 or more independent strings of lights at different rates. I do not believe that the outputs of the BOE kit can power these strings of LED’s directly based upon reading the output stats.
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Is there a low cost product that the BOE kit can control that will operate the light strings? I have been reading on kit74 relay controllers and did not know or did not see reference to projects that used these components together.
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It really doesn’t matter what product brand is required, but the basic programming and price of the BOE is fine for my initial project, I just don’t know where to or what to use to connect the system based upon power handling to the lights.
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I hope enough info is included to get the point across and thank you in advance for any input. If I am on the incorrect path, or if you know of a easier and less expensive way to create a simple programmable lighting circuit please advise.
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Again thank you for your time and assistance.···

Mike Green
02-08-2007, 01:41 AM
If you're talking about strings of LEDs designed to run off standard AC, then you need what's called a Solid State Relay. These look like a single LED to the Stamp, but contain an isolated AC switch, much like a wall dimmer (without the dimming feature). The main problem is that you're combining wiring for AC (very dangerous) with low voltage wiring that you're likely to fiddle with

If you're talking about strings of LEDs designed to run off DC voltages (maybe 12V or so), then you need a simple transistor switch. The What's a Microcontroller? tutorial shows how to do this in terms of controlling a motor or solenoid. It's much the same thing.

I suggest you look into an integrated circuit made by Texas Instruments - the TPIC6595 (look for datasheets on the internet). It works like the 74HC595 which Parallax carries and is discussed in some of their tutorials, but includes high power MOSFET drivers that can be used to switch series connected strings of LEDs. It's a serial shift register that would allow a Stamp to control lots and lots of LEDs while using only a few I/O pins.

If you want to limit what you use to stuff Parallax carries, you could use the 74HC595 plus a ULN2803 Darlington array which functionally would provide the same capability as the TPIC6595.

RDEjr8
02-08-2007, 02:03 AM
Mike thank you for the reply,
Yes the strings are AC
I was hoping that the Stamp could run the program, and would be the input to a relay or device and then the relay or device would handle the power requirements of the LED light strings. I really couldn’t find reference projects to figure out what relay or device to use as the middle man. I am not necessarily addicted to any particular brand, but at the same time I don’t want to abuse this forum for info that doesn’t relate to the Parallax product line.
Thanks again
Tracy

Mike Green
02-08-2007, 02:37 AM
The Industrial Control tutorial www.parallax.com/dl/docs/books/edu/ic.pdf (http://www.parallax.com/dl/docs/books/edu/ic.pdf) briefly discusses solid state relays (SSR). The one they show in the appendix is for relatively high power loads (maybe 10A). You can get lower power SSRs, like 1.5A that are more compact, cost about $4 each. Even Radio Shack used to sell one. Look at Jameco's on-line catalog for examples.

RDEjr8
02-08-2007, 02:41 AM
Thank You very much, this info will hopefully get me building my project
Tracy