[Review Request] 6-Axis CNC Controller - ESP32-S3 & MCP23017 - First Design

[As_Des_As]

Hi everyone,

I’m an engineering student designing a 6-axis CNC controller for my milling machine (2.2kW spindle, 24k RPM). This is my first PCB design, and I’ve spent time cleaning up the schematic and layout based on initial feedback.

Project Specs:

• MCU: ESP32-S3 (FluidNC).

• I/O: MCP23017 via I2C for extra axes and limit switches.

• Isolation: TLP281-4 optocouplers for all Step/Dir signals.

• Power: 24V input with an LM2596 buck converter for 5V/3.3V rails.

Specific Questions:

1. Optocouplers: I initially used 2.2k resistors for 3.3V logic, but I’m worried about speed. I’m considering 470 ohm instead for better switching performance at high RPM. Thoughts?

2. EMF Noise: With a 2.2kW spindle, is my grounding strategy for the ESP32 sufficient?

3. USB Block: I’ve corrected the CH340C VCC connection to the +5V rail. Does the decoupling look okay?

   
   
   
   

Thanks for your time!

[phil_from_seattle (phil barrett)]

TLP281 has a Toff time of 40 uS at 5V. That puts a hard limit of 25 kHz on any signal though it’s likely lower than that if driving at 3.3V. You might be able to get better performance if you play with the pullup resistor. Most stepper drivers support up to at least 200 kHz. In comparison an Arduino running Grbl is limited to about 30 kHz which is generally considered insufficient by the CNC crowd.

A lot of stepper drivers work better with 5V inputs.

BTW, the schematic you posted is so low rez I can’t get much from it.

[As_Des_As]

Thank you for the advice, I’ll definitely check that! As a new user, I wasn’t able to upload a PDF of the schematic, so I apologize for the low quality. I will repost a high-resolution version (PDF) very soon.