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 Best way to control multiple 1.5v lights including brightness (basic stamp)
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By: Anonymous: johnbot () on Sunday, June 17 2007 @ 04:42 PM PDT (Read 3373 times)  
Anonymous: johnbot

Hi Evil Mad Scientist,

Figured I might as well post a question here to get things going....


I've got multiple 1.5 volt hobby type grain lights for which i need to control on/off status and individual brightness. Currently, I have them hooked up to a uln2803 but that doesn't allow me to change the light intensity. Is there some type of chip that i could shift intensity values into or something like that to control all these lamps individually? (7 lamps) What are my options here? What about a digital pot(s)? I'm looking for something very basic....


thanks peeps!





       
   
By: Windell (offline) on Monday, June 18 2007 @ 01:53 PM PDT  
Windell

Sheesh, why not use LEDs and make life easy? Wink

Actually, it sounds like you've already got your lamps under (simple) control with the uln2803, so you're most of the way done already. From your post title I infer that you have a Basic Stamp handy. So, unless I'm missing something, you should just be able to take seven outputs of the Basic Stamp and use those to drive seven inputs of the uln2803. Once you've done that, you have arbitrary control of which lights are on at any given time. You can get intensity control this way as well by reducing how much of the time each light is on, using pulse-width modulation. Suppose that you want one of the lights to be half as bright: just run it with a 50% duty cycle, 1 kHz square wave. If you reload the entire 7-bit output array once every ms (not difficult on a microcontroller), you can control a wide range of intensities, by varying the duty cycle.

Alternative plan: You can use a parallel-output shift register like the 74hc595 to translate seven sequential values into seven parallel outputs. Advantage: Uses fewer pins of your micro. Disadvantage: much slower, so you will be only able to get a few levels of intensity.


Windell H. Oskay
drwho(at)evilmadscientist.com
http://www.evilmadscientist.com/

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