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Driving a dimmer — Parallax Forums

Driving a dimmer

Scott MScott M Posts: 43
edited 2005-03-11 14:09 in General Discussion
I have (well, I will) a light dimmer that takes 0·to +10v input, for off to full bright. I'd like to control this from a Javelin.

First, is it reasonable to take the output of a (PWM) Javelin pin, put it through a 1K resistor into the base of a 2n2222 with the collector tied to a +10v supply and the emitter leading to the dimmer? The dimmer claims an input impedience of 4.7k, so presumably this design doesn't stress anything too much. (Presumably I also need a small cap to smooth out the PWM - I don't know how dimmers respond to being jerked on and off hundreds of times a second...) Have people done equivalent things?

Secondly, since I have 4 of these to drive, does anyone know of a source of NPN transistor DIP arrays that are roughly equivalent to 2n2222's? I wouldn't have thought this hard to find, but web searches turn up obsolete parts...shocked.gif

Is there a better/smarter way to do this?

Scott M

Comments

  • Jon WilliamsJon Williams Posts: 6,491
    edited 2004-09-10 21:31
    The Javelin PWM isn't like the BASIC Stamp PWM (which IS designed to create an analog output through an RC circuit). You might consider controlling a digial pot with the Javelin, the output ("wiper") feeding your dimmer device.

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    Jon Williams
    Applications Engineer, Parallax
    Dallas Office
  • Scott MScott M Posts: 43
    edited 2004-09-10 23:23
    >The Javelin PWM isn't like the BASIC Stamp PWM (which IS designed to create an analog output through an RC circuit). You might consider controlling a digial pot with the Javelin, the output ("wiper") feeding your dimmer device.

    Um.. ok. How is PWM different than PWM? And can you recommend a digital pot I can use to generate 0-10v?

    (I've been using the Javelin to drive a (different) dimmer, which is less fussy about polarity, by putting it through a ULN2003. It's been working, more or less.)
    ·
  • Jon WilliamsJon Williams Posts: 6,491
    edited 2004-09-11 00:52
    The PWM output from the BASIC Stamp does not have a fixed high time versus low time for a given duty cycle. If, however, you look at a sample window of the output, then the accumulative high time versus accumulative low time does indeed match the specified duty cycle. The purpose of the BASIC Stamp PWM is to charge an RC circuit for analog output.

    The PWM from the Javelin is more traditional (like you'd use for motor control). It may well work as you've got it hooked up -- I've not tried. Forgive me if I sent you astray (many customers try to use the BASIC Stamp PWM to drive motors which it's really not designed for).

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    Jon Williams
    Applications Engineer, Parallax
    Dallas Office
  • Brian MillerBrian Miller Posts: 25
    edited 2004-09-14 17:30
    What kind of dimmer are you using?

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    Newbie, using the NX-1000 24/40 Board with a BS2p40
  • Scott MScott M Posts: 43
    edited 2005-03-11 14:09
    a NSI DDS5600
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