I have done a project very similar using the Velleman
kit dimmer module. I was using the basic stamp at the
time, but you will get an idea of how it works.

I used a IR sensor to control the light voltage going
through the Vellamen dimmer kit.

Here is the link to the documentation page which has
all the circuits and some good images.
http://a.parsons.edu/~alison/spring2003/majorStdio/week6.html

- lewischicken

--- James Tu <james@2-BIT-TOYS.COM> wrote:
> Thanks everyone for the wonderful advice.
>
> I think I will go using PWM with a logic-level FET.
>
> -James
> P.S.  a drain in a BJT?  It was late...I think there
> was a drain in the
> B-R-A-I-N.  :)
>
>
> At 03:34 AM 12/5/2003 -0800, you wrote:
> >What is the best way to control the dimming of a
> 12V bulb?  (I have a
> >12VDC halogen bulb rated at 20W)
> >
> >I saw circuits on the web using a digital pot to
> control a LM317 (variable
> >voltage regulator).
> >I also saw circuits on the web using PWM to control
> the bulb via a transistor.
> >
> >I tried the second method...using PWM from my
> microcontroller to control a
> >MJE3055T.  12 V supply is connected to one lead of
> the bulb, the other
> >lead of the bulb is connected to the collector.
> the drain is connected to GND.
> >
> >The transistor got _really_ hot and the bulb was
> hardly lit...it just
> >glowed a bit.  Do I just need a transistor with a
> higher amp rating?
> >Here are the specs for it...
> >VCEO Collector-Emitter Voltage (IB = 0) 60 V
> >VCBO Collector-Base Voltage (IE = 0) 70 V
> >VEBO Emitter-Base Voltage (IC = 0) 5 V
> >IC Collector Current 10 A
> >IB Base Current 6 A
> >Ptot Total Power Dissipation at Tcase # 25 oC   75
> W
> >
> >It seems like it should be fine.  60V and 10A.
> What am I doing wrong such
> >that the transistor is heating up so much?
> >
> >
> >Or should I just try the LM317 approach?
> >
> >The least parts the better...it seems like the
> transistor approach would
> >be best.  Can someone a circuit for this and also
> recommend the transistor
> >to use?
> >
> >Thanks!
> >
> >James Tu
> >james@2-bit-toys.com
> >
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> >
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> James Tu
> james@2-bit-toys.com
>
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