slow dimmer

Looking for a nifty circuit to ramp up and down the brightness of an LED over a period of say 30 mins to an hour. The dimming bit is trivial with a

555 or similar but has anyone got a neat way to do the long time constant bit? I could probably program a PIC to do the lot but I'm sure someone out there has done it the hard(ware) way before?
Reply to
CWatters
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The dimming bit is trivial. So you are aware of the variable charge/discharge circuit of the 555 that adjusts duty cycle.

How about using a second 555 to slowly ramp a signal to a mosfet output opto coupler to adjust one of the duty cycle resistors. A 555 can be made to work over a period of an hour with careful selection of components. If that idea isn't to your liking it would be relatively easy (trivial) to use a fet input op amp to generate a ramp.

The mosfet output opto couplers are good for linear signals, and can be treated like a variable resistor.

Reply to
default

Try the "fading red eyes" circuit at this address:

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The LEDs fade up and down at about a 1 second rate, but you can extend that to a half hour or more with a larger cap and resistor.

-Bill

Reply to
Bill Bowden

Thanks, I'll take a look. Just for info... The LEDs are providing illumination for a web cam inside a bird box. I figure the birds are less likely to be disturbed if the LEDs come on/off slowly at dawn/dusk.

Reply to
CWatters

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