Release note MG firmware update 12353

How to check your firmware version

Let’s get started by checking your current firmware version, using the $I command. Just enter $I into the g-code console of your G-code sender or laser program. For example, if you have the latest firmware version, LightBurn and Mini Gerbil will respond with the firmware serial number 12353, dated 20210410.

To update your firmware, please refer to our firmware updating instructions.

Summary of improvements in MG firmware update 12353

  • Ability to invert logic for PWM ($98) and LO Laser Enable ($99), to cater for non K40 lasers.
  • Bugfix for random “Msg door” messages. Ability to enable/disable door functionality, now disabled by default.
  • Bugfix for motion speed. Increased the stepper motor speeds from 200mm/sec to 400mm/sec.
  • Bugfix for motor step driver duration. Previously the step duration was fixed to 10mSec. Now the user can define the step duration in $0. Default setting is 10 milliseconds.
  • Replace the Fault output with Air Assist function.
  • Microcontroller stack size increased – an under-the-hood improvement.

Detailed information

PWM and LO logic extension.

The stock K40 laser uses negative logic (logic 0 to operate) the LO laser enable signal, and the Mini Gerbil firmware was designed accordingly. We have updated the firmware to allow use of positive logic (logic 1 is used to operate) for the LO signal. This extension is useful for people with a DIY laser build that requires positive logic and avoids the need to add additional hardware e.g. inverter boards. After setting the $ setting, the logic is applied immediately and output pins might change and affect the operation of the laser. So please switch off the laser before changing the $ settings or make sure that safety precautions are taken.

For completeness, we also implemented a similar configuration option for PWM. PWM is positive logic by default, and the opportunity has been added to invert it.

The $ settings are:

  • $98=0  (default factory setting for K40) sets PWM to positive logic (gcode S parm = 0 produces 0 volt, S=1000 produces 5 Volt). At rest or startup of the MG controller, the PWM signal is zero or 0 Volt.
  • $98=1 Sets PWM to inverted output (gcode S parm = 0 produces 5 volt, S=1000 produces 0 Volt). At rest or startup of the MG controller, PWM is logic value 1, which is 5 Volts.
  • $99=0 sets LO “laser on” to positive logic (turn on sets LO to one or 5Volt). At rest or startup of the MG controller, the LO pin is zero or 0 Volt.
  • $99= 1 (default factory setting for K40) Sets LO “laser on” to negative logic (turns the laser on via setting the LO pin to zero or 0 volt). At rest or startup of the MG controller, LO is logic value one, which is 5 Volts.

Message Door Bugfix.

Occasionally users have reported that the “Msg Door” message randomly pops up despite no door or lid switch installed on their controller. We believe this is a grbl glitch which was ported to Mini Gerbil firmware. The firmware now only enables the Msg Door functionality if $97=1. The default value is now $97=0. See related blog.

Motion speed Bugfix.

The parameters within the motion routines have been reworked to provide more processing for the interrupt routine to generate steps for higher movement speeds. The maximum stepper speed within the Stock K40 laser is now 400mm/sec. Key notes:

  • users might see slower speeds due to tight belts, low current settings of the step drivers or poor factory build like slightly binding rails (skewed gantry builds).
  • the beam power of the k40 laser is insufficient to burn most wood at these high speeds. The laser power limits cutting of most materials to around 200mm/sec.
  • note that cnc systems have ceiling limits configured for velocity and acceleration. To achieve a speed requested in the gcode program, the $ setting configurations for velocity and acceleration must support it.

The bugfix allows correct interpretation of the $0 stepduration configuration.

  • An extra timer has been implemented within the stepdriver interrupt service routine to produce accurate step durations. The timer allows for step duration between 3mSec and 80mSec. The default factory setting is 10mSec, which is to suit the standard A4988 stepsticks that come with the Mini Gerbil. A value of 20mSec has also been successfully tested with the standard stepsticks. Values of 35mSec and above were tested but found to cause erratic behaviour on the standard stepsticks.

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