The digital input is so you can turn this on and off using something like the 4017 circuit shown in post #18. The fewer LEDs the brighter they are, but I think you'll be happy with the schematic as drawn. For 4.5V you must have at least 3 red LEDs in a chain or 2 blue, for more power supply voltage you can have more. The LEDs will slightly glow at 1.5V as drawn.
This is the schematic you posted on post #18. The 555 replaces the transistors.
If you want them to stay on just connect pin 4 to Vcc and eliminate the digital input circuits.
.
This is the schematic you posted on post #18. The 555 replaces the transistors.
If you want them to stay on just connect pin 4 to Vcc and eliminate the digital input circuits.
.