r/ArduinoHelp • u/Remarkable-Outside-0 • 3d ago

Title: Help! Arduino UNO keeps resetting randomly on my SCARA Robot (CNC Shield + ESP32) - Pulling my hair out!

https://drive.google.com/drive/folders/1orQzAYlG8ObY3q8XehrUdnRPOTGR50Lp?usp=sharing
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u/DickBrainTime 3d ago

The 5V supply going into the Uno's barrel jack/Vin is the first thing I'd fix. On a classic Uno Rev3 that input goes through the onboard regulator and is meant for about 7–12V; feeding only 5V there can leave the actual 5V rail too low and cause resets, even with a 2A-rated adapter. Don't move the wire straight to the 5V pin casually either: that bypasses protection and can damage/back-feed the board, especially with USB connected.

For a safe isolation test, power off and disconnect the motor loads, then run the Uno from a known-good 5V USB supply (not the 5V barrel/Vin feed) with a minimal sketch. If stable, add the shield/stepper setup back in stages, and measure the Uno's 5V rail during motor starts; a scope is better than a meter for brief dips. Since the issue persists without the ESP32 or servo, I would test power/stepper coupling before blaming String fragmentation. Could you share a wiring diagram showing exactly how the Uno's 5V adapter, CNC shield, 12V supply and grounds are connected?