Automatic Dimming Nightlight

By Jason Poel Smith
Category: Electronics
Time Required: 2 to 4 hrs
Difficulty: Moderate

A lot of people find it easier to fall asleep with a dim light such as a nightlight in the room. But the down side of most nightlights is that they waste electricity because they are on all night when you really only need them to be on while you are falling asleep. So I designed a nightlight that will automatically dim and turn itself off.

Here is a brief video of the build:

Steps

Step #1: Circuit

The circuit can be broken into two main parts, a timer circuit and a dimming circuit. The timer (left) is made from a 741 OP AMP wired as a comparator. The dimmer (right) is made from 741 OP AMP wired as a voltage follower (or a unity gain amplifier)

7 Responses to Automatic Dimming Nightlight

Jason Poel Smith on November 19th, 2012 at 3:09 pm said:

To reverse the circuit, all you have to do is connect the output LED’s to the positive supply voltage instead of to ground (and reverse the orientation).

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Jason Poel Smith on November 19th, 2012 at 3:15 pm said:

There are programmable dimming switches that are available commercially. There are a lot of circuits that you could design to do the same thing. But if you don’t care about the dimming being gradual, you could just use christmas light timers. I have two lights set up with timers for my finch aviary. The first timer turns on one light (half brightness) and the second timer turns on the second light (fully brightness). Then at night the opposite happens as they time off.

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Jason Poel Smith on December 30th, 2012 at 8:29 pm said:

You can use a double-pole-double-throw (DPDT) switch. Attach the LEDs to the center pins and set the other pins based on how you would like the LEDs to be connected to the output. Here is an example:
http://www.flickr.com/photos/66422585@N04/8327320834/in/photostream

This setup reverses the output when switched.

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Jason Poel Smith on January 30th, 2013 at 2:55 pm said:

The simplest way to modify the design is to add a more powerful AC adapter and add a power transistor to the output. Unfortunately it can be difficult to find wall adapters that are rated for 3 watts. You need to add a power transistor between the IC and the light because the IC is only rated for .5 watts.

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Jason Poel Smith on February 5th, 2013 at 8:50 am said:

I can’t really advise on how to wire it up without knowing what specific parts that you are going to use. I recommend looking up designs for transistor amplifiers. A simple google search should get you some suggestions.

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Vicky on March 14th, 2013 at 12:36 pm said:

I want to use lamps, like of 100 watts! I want them to dim gradually in the next 30 secs and then brighten up in another 30 secs! And repeat! Possible?

Suggestions? Can I tweak the same circuit?

- Vicky!!

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Dave on May 23rd, 2013 at 11:00 am said:

There is a third main part: The wall wart that powers it, and probably idles at just as much power as a few LEDs.
If you really want to save energy, selection of the primary power supply is critical.
I would also suggest using low-power opamps. The venerable workhorse 741 is pretty hungry by more modern standards. A FET-input amp will also make the long duration timing easier, with smaller caps.

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