Today we made a controller to turn on the navigation lights on a radio controlled helicopter when it is dusk or dark outside.

Being a small RC helicopter, the lighting controller had to be small in size and low weight. A basic transistor circuit with light detector would not have been up to the job since the navigation lights would flicker on and off when the light detector was at the ambient light/dark threshold. The controller therefore needed hysteresis to avoid this multi-switching. It also needed to be easy for the user to set the light/dark threshold at which the navigation lights turn off/on.

To keep everything small, we used a PICAXE-08M2 microcontroller for this project. To set the light/dark threshold we decided against using a potentiometer in case vibrations from the helicopter’s motor caused it to rotate away from the user set position. Instead we fitted a small tactile switch to the circuit board. If this is pressed and held (at dusk) while the controller is being connected to the battery pack, the light detector (mini LDR) measures the current ambient light level and stores this in memory (not lost when battery disconnected) as the light/dark threshold.

In standard operation, when the light level is measured to be brighter than the threshold continuously for two seconds, the output to the navigation lights is turned on. If subsequently the light level is measured to be duller than the threshold continuously for two seconds, the output to the navigation lights is turned off.

The dimensions of the controller are under 2 x 2 inches.