Re: Flashlight dimmer for cave photography?

From: JeffM (jeffm__at_email.com)
Date: 07/04/04 

Date: 3 Jul 2004 22:14:10 -0700

>>>>>PWM (pulse-width modulation) - your steady-state is a stream of
>>>>>pulses with a duty cycle proportional to your desired light level
>> Rich Grise
>
>This is exactly what I was thinking. It's just like pinching a garden
>hose periodically to govern the water flow.
>Brian
>
Only if you can pinch and release VERY quickly. 8-)
PWM works by integration at the load.

>How about a capacitor
>(expandable rubber section in-line to absorb the inrush volume) in-line
>to avoid jarring and fatiguing the filament?
>
If you mean ramping up the duty cycle to its final value, OK.
Doubt it would have much effect.

>>halogens hate being dimmed.
>>OK, they don't hate it, but the bulb life is significantly reduced.
>
>Get out of town?!
>
Agreed.

>>But, if I read the post correctly,
>>the halogen light is to be turned off before the picture is taken
>
>Actually, it is the flash signal which would turn it off.
>This secondary light would help focusing
>and also [sic] reduce the power of the central flash
>
>>Ah! Then just a Watson Name flashlight with a pot or 555 PWM,
>>and just a "bright-<~.5s>-Shoot-Off" sequence sounds like it would
>>work. :-)
>
>Huh?
>
A reference to Watt Sun.
http://groups.google.com/groups?q=Watson-a-Name+LEDs+flashlight

Take a FET that will handle the current of your bulb,
with its gate driven by the 555 astable.
A photosensitive latching circuit could reset the PWM.

555 basics
http://groups.google.com/groups?&threadm=409176DB.58946793@rica.net

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