Before you plug it in
Zikro reads the real connectors on both devices, compares levels, impedances and supply rails, then says in plain language what will happen. When something is wrong, it computes the fix.
An Arduino Uno R3 drives its data line to 5 V, and the ESP32 DevKit V1 pin it lands on, GPIO 21, is rated to 3.3 V. The input clamp conducts on every high bit and the pin degrades. Zikro sizes the divider for you: 2.2 kΩ in series, 4.7 kΩ to ground.
Every verdict cites the device profile it came from, and how confident that profile is.
Give us the address on the account and we will send a link.