Penta-Fade

Questions

1. How can you predict the rate that LEDs will fade relative to each other?

2. Why does each branch of the circuit need to have a 1N4001 diode?

3. Why do all five branches draw the same current after the button has been held for a short time?

BONUS: How could you modify the circuit to use PNP instead of NPN transistors?

Schematic

PCB