smart switch circuit

Smart Switch for Model Aircraft Lights

model aircraft

The Smart Switch for Model Aircraft Lights is a simple yet efficient ambient light sensing electronic switch designed to be user programmable over a wide range from full sunlight to total darkness including an always on setting option. Infact, the switch is an improved version of the predominately exploited conventional automatic twilight (dusk-to-dawn controller) switch circuitry. The built-in light sensor element continually monitors the ambient lighting conditions and reacts to turn a light circuit either on or off. The switch, uniquely designed to be tucked away inside a model, is quite versatile and can be used for a variety of lighting control applications in radio-controlled model aircrafts.

About Model Aircraft Lights

Now a days cluster LED lights (4.8v – 6v) are widely available for model aircraft applications. They are bright enough to be seen from afar, so we can use several to mark out different points on our model aircraft. For example, a white light to mark nose, and green/orange lights to mark left/right wings. A quick reference guide on model aircraft navigation/landing lights is also included here for the sake of novices.

model aircraft night lights

(model aircraft night flying/navigation/landing lights)

Note that, total 8 LED lights are required in a model aircraft; anti-collision red beacon, strobe white lights, navigation lights (left side is red, right side is green), and landing lights. Usually, these lights are powered from 4.8v- 6.0v dc supply available from the receiver.

  • x 1 always on (steady) green light (front starboard wing: navigation)
  • x 1 always on (steady) red/orange light (front port wing: navigation)
  • x 2 flashing (blink) strobe white lights (rear wings: navigation)
  • x 1 slow flashing (blink) red strobe light (fin: beacon)
  • x 3 always on (steady) white lights (front wings and nose: landing)
model aircraft lights

(model aircraft night flying/navigation/landing lights – quick reference)

Usually navigation lights are connected to the receiver’s throttle jack or any spare R/C channel, and clever arming tricks are used to share the throttle stick profile. Similarly, the strobe lights are worked at standard single blink (85/min), or special double wink (60/min) patterns.

About Smart Switch Circuit

Smart Switch circuit is wired around the popular LM555 chip (IC1), here configured as a light/dark sensor switch for driving an electromagnetic relay (RL1), based on the status of a photoresistor (LDR). The multi-turn preset potentiometer (P1) included in the circuitry can be used to adjust the overall detection sensitivity of the circuit to a great extent. Toggle switch (S1) connected across the relay contacts picks out the mode of operation; auto mode or always on mode.

The circuitry can be built using nearly any technique you wish. Mine was built on a small phenolic perfboard. Perfboard layout is not critical except that the first 100nF capacitor (C1) should be close to the 555 IC. Double check your work, especially the power connector and IC1 pins 1 and 8. Simple mistakes can destroy electronic parts and ruin your day. After construction, enclose the finished circuit in a high impact ABS/ Plasticized Rubber case. Smart Switch is easy to install and operate. First of all mount the switch box in your aircraft in a suitable location, and connect 5 volt (4.8- 6.0) power cable to the input (DC_IN) of the circuit. Next, fix the aircraft light(s) in position and then connect the leads to the switch socket (SW) as indicated in the circuit diagram.

smart switch circuit

(smart switch – circuit diagram)


  • Read the user manuals carefully before installing and using your model aircraft lights
  • Do not supply voltages beyond the above recommended voltages
  • I have not fitted a power on/off switch in my prototype. So it is not shown in the schematic and if required (depending on how you use/power the circuit) should be inserted in the +5V rail
  • All information is provided as is. I do not offer any warranty on its suitability. If you build and use this circuit, you will do so at your own risk

The No-Frills Version

Here is a no-frills version of the smart switch circuit, built around generally available low-cost transistors. Needless to say, this is a solid-state switching circuit because no moving-parts/components are used here. Since a transistor is used as the switch, keep an eye on its current handling capacity. If you need more current (to drive more aircraft lights) you will need to change the switching transistor as demanded by the situation.

smart switch no-frills

(smart switch – no-frills version)

Flying R/C models at night has become popular in recent years. Not only is it a quite fun but nighttime visual aspects give your model aircraft a more realistic appearance. However, be aware that flying model aircrafts at nighttime require additional safety measures. So remember to consult the concerned authority before you take to the sky.

night-drone fitted

(night-drone fitted with author’s smart switch prototype)

Power LED Model Aircraft Light

Now a days, it is very easy to build your own model aircraft lights using standard 1W LEDs and dedicated LED drivers. Here is the tried and tested circuit diagram of a 1W LED model aircraft light comprises a 1W white LED and an power LED driver chip AMC7135 (low dropout current regulator rated for 350mA constant sink current). The circuit can be powered from 4.8v- 6.0v dc supply available through the onboard receiver or through a separate dc power supply. Since the LED is white in color, we can use clear/desired color round-domed caps for the light. Circuit given here strictly follows the application data of AMC7135. If you want to modify the circuit design, refer datasheet of AMC7135 (from ADDtek/ for more features, application tips, etc. Note that, in the prototype, LED and AMC7135 is located on the same PCB, so a 100nF capacitor is used as C1. Typically a 1uF-10uF capacitor is highly recommended if the LED is located far away (> 3cms) from the AMC7135 chip.



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