I stumbled upon a very badly drawn circuit on the interent which must be good . I have not been able to figure out how a series of transistors work in this circuit. It is depicted below.
When this circuit powers, the leds turn on and stay on one by one until the last led is turned on, and then they all go off and the cycle starts over again. My question is in regards to if someone could explain to me why this behavior happen with the transistors. I am not sure how an astable pulse to this array of transistors would cause this cascading behavior.
Best Answer
Improved LED Sequencer Circuit
This circuit has improvements over the posted circuit with the addition of a few more components. Still all simple components!! I did not include the astable oscillator in the simulation but that can easily be built with a 555 or a couple more transistors, resistors and capacitors.
A current source keeps the voltage ramp linear. An emitter follower buffers the waveform to the threshold diode stack and all transistors switch the same current levels to each LED.
The net result of this is that timing steps of the LEDs turning on are much more even and the timing parameters are easily adjusted to get desired timing, whether this be for a turn signal sequencer or for a light sabre flash up.