What is the ULN2003
A Darlington transistor array with 7 channels, designed to drive loads that a microcontroller (Arduino, ESP, PIC, etc.) cannot drive directly.

Main features:

• 7 independent channels (7× NPN Darlington pairs)
• Up to 500 mA per channel (realistically ~300 mA for safety)
• Up to 50 V load
• Built-in flyback protection diodes for inductive loads (relays, motors, solenoids)
• 5V logic input level (compatible with Arduino, STM32, ESP32 with level shifting)
• Common diode pin (COM) for connection to the positive voltage of the loads.