Re: CNC V3 resistors

Howard Dutton

On Sat, Jan 9, 2021 at 11:07 PM, Ken Hunter wrote:
Checking the schematics, I see that the SHC (Smart Hand Controller) already has the pullup resistors installed (RP1). The various Home Brew schematics
do not show the pullup resistors. A note should be included in the build that states "the CNC V3 pullups are only required if the hand controller does not  already  include them". A better solution would be to state that "pullup resistors should be included in all home brew hand controllers" That way the possibility of "double pullups" would be eliminated
The RP's in the SHC are not for those signal lines.  If you plan to enable the ST4 port install the pullup resistors.

I'm not convinced that removing the 10K resistor on the CNC V3 is necessary. If it were a 2K resistor the resulting current to the MCU might be excessive but 10K provides only enough current to activate the logic circuitry, not burn it out.
Mike is correct.  The ESP32 is a 3.3V device and that resistor is putting 5V on that stepper driver enable pin.  In general this is not ok and will result in reducing the life expectancy of that pin.  Now that being said some 3.3V devices are designed to be 5V compatible.  According to the datasheet the ESP32 isn't one of those devices though some speculate it has fairly effective protection circuitry built in.

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