I own a decorative light for the winter which I controlled using a simple time switch in the past. The time of dusk is continually shifting, so I had to adjust the turn-on time multiple times each year.

This year, I planned to automate the turn-on time. I tried to find a light controlled switch, which automatically enables the decoration on dusk and disable it on dawn. I saw no suitable one.

I ended adding an own switching circuit to the decoration. This article describes how to build an own controller as I did and highlights a few problems you may encounter.

The Issues with Off-the-Shelf Solutions

My requirements for the off-the-shelf solutions were:

  • Setting to adjust the light level.
  • Suppression/identify the light from the decoration.
  • Turn off at a given time or dawn.
  • It shall work at a temperature of -10ºC.

Sadly, I found no simple device, which matched all my requirements. I also noticed, most of these devices had horrible ratings and reviews – mainly because they lacked the described features.

Adjusting the light level seems a straight forward requirement. The brightness, where you like to turn the decoration on is a matter of personal taste. Most devices I found do not let you adjust this.

If the decoration is turned on, it will naturally get brighter outside. If the switch does not compensate for this fact, the light will start to blink. In this case, you had to place the sensor somewhere carefully it is not affected by the light of the decoration.

Most devices just let you select a duration, how long the light stays on. This is the cheapest way to implement a device like this. It makes not much sense though. Because the time of the dusk is moving, the time when the light turns off shifts as well. Useful is either turning the light off at dawn, or at a fixed time.

Then, there I found one device which had all the previous features, but it was rated to indoor use only. The minimum working temperature was 5ºC.

Initial Situation

The initial situation is shown in the following illustration:

A timer connects to the mains plug. The mains adapter of the decoration connects to this timer and converts the 240V AC power to 24V AC. This AC voltage is somehow a standard way to power old, filament lamp based decorations.

Continue Reading