Neon flashing 🎄 Christmas Tree
A neon lamp is simply a small glass tube filled with a low pressure such as
neon or sometimes with additional small amounts of krypton, argon, etc. to change the color from
the normal orange.
The NE-2 will fire at around 90 volts DC, then the operating voltage will drop to
about 60 volts. This produces an odd effect known as negative resistance. That means once
it conducts the resistance will drop and the operating voltage is much lower than the
ignition voltage. The lamp will stay on until the voltage drops below 50 volts or so. The
cap gets drained of charge faster than the resistor can recharge it, thus the bulb will go out
when the charge is depleted enough to drop below that 50 or so volts.
Then the resistor slowly recharges the cap to the firing voltage.
This property allows neon lamps to be used with resistor/capacitor charging circuits to
create a relaxation oscillator. The waveform approximates but is not exactly a sawtooth, as the rising ramp is not
straight, but is a
portion of an RC charging curve.
This Xmas tree uses 5 independent flashing circuits, creating a random flashing pattern.
Differing resistor values make for differing flashing rates, enhancing the random effect.