Semi-random LED flashing 🎄 Christmas Tree circuit
There are two independent circuits here, one a countdown off the 60Hz powerline frequency
(several divide by 2
flip flops in series), and the
other a free running astable 555 circuit. The counddown makes 50% duty cycle square waves, and the 555
makes 66% duty cycle square waves. We can cross connect various LEDs between the 555's output
and various divide downs of the countdown circuit. This creates a semi-random pattern
for the LEDs to light or not over time. The LED will only light up if its cathode is more
negative than its anode, so this creates a kind of AND function (where one of the AND gate
inputs is inverted). There are no actual AND gates here, the LED diode does that for us.
See the "LED lighting Truth Table" in the lower left of the below diagram. In the lower right
of this diagram is timing waveforms, showing the resulting time pattern when the LED lights up.
The timing of the countdown and the 555 circuits are independent and thus random to each other.
This makes for a random-ish blink pattern of the LED, maybe two quick blinks and a longer period of being off,
or other times one longer blink.and an off period. Look at the yellow LED (the topmost one) in the picture
above. Other LEDs are a mix and match combination of various outputs of the countdown flip-flops
and the 555. Yields other flashing time patterns.
As my entire circuit is self contained and
enclosed in a plastic box,
I used a "hot chassis" power supply circuit.