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Automatic Dimming Nightlight

A nightlight that automatically dims and turns itself off after a set period of time.

Automatic Dimming Nightlight

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:


Step #1: Circuit

Automatic Dimming Nightlight

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)

Step #2: Timer circuit

Automatic Dimming Nightlight
  • The timer is made from a 741 op amp (operational amplifier) wired as a comparator. It compares the voltage across a capacitor with a reference voltage that is set by the 2.2k resistor and the 5k potentiometer.
  • When S2 is pressed the capacitor is charged to the supply voltage. It then gradually discharges through the 1M resistor. As long as the voltage across the capacitor is greater than the reference voltage, the output of the op amp is high (about 8.7V). When the voltage across the capacitor drops below the reference, the output of the op amp goes low (about 1.9V). This can take 0-45 minutes depending on how the potentiometer is set.

Step #3: Dimmer Circuit

Automatic Dimming Nightlight

While the output of the timer is HIGH, it keeps the second capacitor charged. When the timer output goes LOW, this capacitor begins to slowly discharge through the 3.3M resistor. This begins the dimming cycle. The output of the second 741 op amp mirrors the voltage across the capacitor. As the voltage across the second capacitor drops, so does the output voltage and the LEDs dim. It should take about 45 minutes for the LEDs to go from full brightness to full darkness. Pressing the button at any point will reset the whole cycle.

Step #4: Breadboard Prototype

Automatic Dimming Nightlight

Testing your circuit on a breadboard before soldering can help work out bugs.

Step #5: Solder the circuit together on the circuit board.

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Then if the breadboard prototype works, solder it onto a circuit board. In order to conserve space I am stacking some components. When you are done soldering, trim your board to help it fit in the housing.

Step #6: Add surface components.

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To connect the variable resistor, I am using a strip of PC jumper wires with some of the wires trimmed off. For my light source I am using three LEDs in series whose combined voltages is close to the supply voltage so I am forgoing adding a resistor. I tend to use a lot of heat shrink tubing to insulate my solder connections. I find that it helps avoid unwanted shorts.

Step #7: Find/make a suitable housing

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Once you have the circuit constructed, find a suitable housing. Then drill some holes for the LEDs, the switches, the dial and the power cord. Trim your circuit board so that it is only as big as it has to be. This will really help when it comes to fitting everything in the housing. Finally, load in all the components and your project is complete.

Step #8: Test the finished product

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The last step is making it look nice. If you want, you can added a diffuser or something to scatter the light. You can tint the LEDs using gels or just liquid highlighter. The final aesthetic details are up to you. I put mine in a decorative lantern.

Step #9: Modify the design

Automatic Dimming Nightlight

The duration of time that the lights are on at full brightness and the time that they dim can be modified by changing the values of R1, C1, R4 and C2. By changing the ratios of the resistors and capacitors you change how quickly the capacitors will discharge. For a decent estimate of how the capacitors will discharge you can use the formula Vc=Vo×e(-t/RC). Feel free to change the values to meet your needs.

Jason Poel Smith

Jason Poel Smith is a helicopter tooling engineer. When he’s not inventing, he’s spending time with his amazing family.


  1. Jason Poel Smith says:

    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).

  2. Jason Poel Smith says:

    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.

  3. Jason Poel Smith says:

    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:

    This setup reverses the output when switched.

  4. Jason Poel Smith says:

    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.

  5. Jason Poel Smith says:

    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.

  6. Vicky says:

    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!!

  7. Dave says:

    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.

  8. Gaurav Kumar says:

    can i get the pcb layout of this plz mail me at my gmail id

  9. Len says:

    I would like to use something like this to power on and off my LEDs on my aquarium… Would this be easy to alter for this?

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