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.
You must be logged in to reply to this topic.