There is 5Volt internal supply of level indicator. The IO drives the LED current to value about 10mA. (2k1 resistor). The 220R resistor drives maximum supply for internal comparators to value about 1,4Volt. There is the switch to bar indicator or dot indicator. The transistor makes the buffer with delay via 22µF capacitor. The 250k trimr sets first LED if NO input signal. The 7805 stabilisator makes 5Volt internal supply. The diode and 470µF capacitor converts AC 7-20Volt to DC for 7805 of level indicator.
Czech resistor values specification:
2k1 = 2100 Ω, 220 = 220 ΩDatasheets
Bipolar transistors datasheets
Display drivers datasheets
Voltage references datasheets