Aircraft Light Controller

Aircraft Light Controller

A simple project using a 555 timer.  Hopefully as bulletproof as it can get.

How it Works:

 

This works by charging the capacitor through the 10k resistor.  When it reaches a threshold level, the 555 output goes low.  The 100k resistor then is the discharge path.  When the capacitor discharges to the threshold point, the output goes high and charges the capacitor.  This creates a pulsing waveform, with frequency around 1-2Hz (I didn’t measure it) and very nice short pulse widths.

The 555 then controls a 2N3905 NPN transistor that drives the LEDs.  Since the entire battery voltage is available, we can have more than a single LED in series, with a simple resistor to control current.  Simple and it works.

Of note, it appears that silicon caulking affects the circuit, likely due to some extra conductivity or capacitance, and stops the lights from blinking.  Otherwise the circuit works fine.  I also need to add some form of protection to stop the battery from being damaged in the event of a short circuit (a fuse should do nicely).  A simple fuse should be sufficient.  As always, use at your own risk.

Limitations

  1. As this project is using very basic components to create what is essentially a clock, frequency stability could be an issue.  It will be interesting to see how the circuit performs in -30ºC weather.
  2. As mentioned above, there is no real protection to the rest of the device.
  3. The PCB is relatively large, using SMT components would drastically reduce the overall size.
  4. A proper PCB would have a much smaller chance of shorts due to objects falling on it.  Interestingly enough, Silicon Caulking is apparently conductive enough to affect the circuit significantly when placed directly on the PCB.

Schematic and PCB files (Eagle Format)

The repository can be found here.