The 555 timer IC is connected for Astable Operation, the clock pulses are fed to the 4017 IC via the
10K resistor. The 4017 is a 10 stage counter, each of the outputs is connected to the appropriate LED,
as some LEDs need to be on for more than one count, we use diodes to avoid a short circuit situation between outputs.|
The capacitor and resistor on pin 15 of the 4017 are used to reset the counter to zero at initial power up.
The ULN2001N used on the bulb version is a seven channel Darlington Driver IC, a small signal on one of the inputs is enough to
drive the bulb on the output.