4.0.5-RC1 Firmware for Original Prusa MINI  

Member Admin

Hi guys,

this is a testing release recommended to experienced users! 

What is new?

  • New EEPROM implementation
  • Prusa Connect Local (WebUI)
  • Stop print function fixed
  • Remote print - OctoPrint
  • Adjustment to Mesh Bed Levelling
  • New color scheme for active button
  • Improved movement near the axis end
  • Revised file sorting
  • Adjustments to e-steps

Detailed description

New EEPROM implementation

Due to historical reasons, the previous firmware releases were using two EEPROM implementations - one provided by stock Marlin, the other for Prusa-specific persistent data. However, this implementation was causing synchronization issues and it was decided to unify both EEPROMs into one. As a result, the support for Marlin's EEPROM is now disabled and upon the reboot, all the Marlin settings are always set to the default values.

Any specific adjustment of those values should be part of the G-code. The only variables from Marlin allowed to be stored in the EEPROM are the Live Adjust Z and PID calibration. The EEPROM further contains Ethernet settings, the filament type and the information, whether the Wizard was successfully finished.

Each variable is now saved independently, unlike in Marlin, where saving one variable resulted in an update to all other variables. The data integrity is now guaranteed by the CRC32. If an error during the check is detected, the EEPROM is set back to the factory defaults, thus the printer has to be calibrated again.

The old and new implementations of the EEPROM are compatible, but only in case of an upgrade. If the user decides for a downgrade from the 4.0.5 to an older firmware a factory reset is recommended.

Prusa Connect Local (Web UI)

Starting with this release, there is a brand new web interface called Prusa Connect Local, designed to provide remote monitoring capabilities. The current version provides an overview of the following:

  • Name of the printed G-code
  • Temperature of the heatbed and nozzle
  • Type of the loaded material
  • Current print speed
  • Current height of the Z-axis
  • Printing / Remaining time


There are more features to come and the web interface will be further updated in the upcoming releases.

Stop print function fixed

The Stop print function was sometimes using incorrect coordinates while parking the print head or the heatbed, this resulted in multiple attempts to reach the end of the axis and chattering sound. This issue occurred mostly while printing large objects and the printer had to travel longer distances. This is now fixed.

Remote print - OctoPrint

When you start a remote print over the popular app OctoPrint, the printer becomes locked and a dialog is displayed on the screen. This is for safety reasons. To control the printer (e.g. temperature adjustment) during the remote print, please use the OctoPrint app or web interface. However, in a critical situation, the user is still able to reboot the printer using the hardware button situated under the screen.

remote printing

Note: The "Live Adjust Z" adjustment during the print is now not available while using the OctoPrint. It will be addressed in the final release.

Adjustment to Mesh Bed Levelling

In some scenarios, we have observed improper readings during Mesh Bed Levelling (MBL). This can be caused for example by a slightly misaligned print steel sheet. To address this issue and possible errors in the future, the outer edges for the MBL were moved 5 mm towards the center of the heatbed. The printing area remains unchanged.

A new color scheme for active button

In order to improve the clarity of dialog windows, the color scheme of the actively selected buttons was changed to an orange background and black font. A typical example is the YES/NO dialog.

Old and new color scheme

Improved movement near the axis end

In the case of the print head or the heatbed being too close to the edge of its axis, the printer sometimes incorrectly detected the current position and continued the movement with a higher power, forcing the motor to skip a step. The algorithm responsible for the detection of the end of the axis was improved to prevent these situations.

Revised file sorting

The file sorting algorithm was improved to handle the files on the USB drive based on the time of the last change. Since every operating system (Windows, macOS, Linux) handles this differently, the printer compares the following times (file creation time and file modification time) and selects the most recent one.

The new sorting algorithm also handles specific situations like:

  • Extracting an old G-code from a ZIP archive
  • Updating an existing G-code file directly on the USB drive

Adjustments to e-steps

Based on the internal testing it was discovered that there is a slight under-extrusion during the print. To compensate for this behavior, the e-steps value was adjusted by 2.5 %.

Supported printer:

  • Original Prusa MINI

Download link:


How to flash the firmware on MINI:

  1. Copy the firmware file (.bbf) onto the USB drive with FAT32 formatting
  2. Insert the flash drive in the MINI's USB port
  3. Turn the printer ON (or reset it)
  4. A new screen will appear
  5. Confirm you want to flash the firmware
  6. Wait till the firmware is flashed and printer fully boots into the homescreen

Please report any bug here:


As always, we wish you happy printing and look forward to your feedback!

Assembly manuals / Knowledge Base
The guy behind Prusa assembly manuals......
Posted : 23/03/2020 9:28 am
Matteo Cristini
Estimable Member

Thank you for the update!

Do you happen to know when we'll finally get wi-fi support?

Posted : 23/03/2020 12:57 pm
Eminent Member

“If the user decides for a downgrade from the 4.0.5 to an older firmware a factory reset is recommended.”

This isn’t trivial if you need to back out of this firmware upgrade. 

Posted : 23/03/2020 3:24 pm
Estimable Member

my understanding is that the only thing currently stored in eeprom is the live Z value  thus a factory reset does not affect many parameters or am i wrong

Mini with FW:4.0.5RC1...
Posted : 23/03/2020 4:23 pm
Trusted Member

Very nice updates! I was waiting for that WebUI. The black color looks really good. ☕ 

Posted : 24/03/2020 4:38 am
Trusted Member

Some nice new features 🙂

I seem to have an issue with Prusa Connect, my web browser shows the web page, but the data presented is old data from a previous print, and is not updated. The temp graph scrolls, but with "stuck" temps. Maybe a caching issue?

Is there a way to get the data direct from the printer without the web browser?

Posted : 24/03/2020 12:47 pm
Trusted Member

It seems that Prusa Connect Local used to work in Firefox, before it updated to version 74.0 (Windows 10; 64 bit). Now it always displays some cached data, I tried clearing cookies in Firefox with no effect. The Mini webpage is a big blob of Javascript, so who knows how that works 🙂

Prusa Connect is working in Microsoft Edge, so that is an acceptable workaround.

Posted : 24/03/2020 4:06 pm
New Member


Have you tried to disabling Enhanced Tracking Protection inside Firefox?

Posted : 25/03/2020 11:38 pm
Estimable Member

I saw an error while printing so I hit "Pause" to check it out.  I then hit "Stop" because I forgot to add a support.

It seems like hitting Pause, and then Stop immediately after causes weird behavior.


Is anyone else seeing this issue?


All your filament are belong to us!...
Posted : 26/03/2020 11:46 pm
New Member


Seems to me like it resumes from pause state after you clicked "stop", to then stop the print. Can't reproduce because my mini will be here in maybe july? :/




Posted : 27/03/2020 11:24 am
Active Member
  1. Does this also include scrolling filenames? The screen is to small for those filenames generated by prusa slicer for example .
  2. Will we get a beep indicating finished prints?
Posted : 28/03/2020 1:35 pm
Trusted Member


Second these two points. Number 2 would be nice to have, although not essential. Number 1 is a "must-have". I frequently have many different file versions but they all look the same on the screen because of the character limit. It wastes a lot of time to have to actually select one, then to have to back out to the selection list to select a different one. MK3/s handles this very nicely, why not the Mini?

1. "Every creative act results from a sudden cessation of stupidity." -Edwin Land, inventor of the Polaroid Land Camera. 2. "The experiment can always be solved with the materials in the room." -My college physics professor. 3. "If…...
Posted : 28/03/2020 10:27 pm
Reputable Member

I agree that the complete filename should be shown, either as scrolling or wrap around - the Mini display has higher resolution than i3 and that is showing a lot more of the long file names.

Issue on long names: Add long filename scrolling #249

Take a look at my designs on Thingiverse or on PrusaPrinters ;)...
Posted : 29/03/2020 12:02 am
Eminent Member

Question regarding Prusa Connect. Have the filament sensor hooked up by the Web UI shows it as "NA". Any ideas?


Posted : 30/03/2020 1:11 am
Active Member

Nice features! Maybe a warning during flashing would be nice though, not everybody knows that you brick your device if you turn off power while flashing.

Posted : 30/03/2020 1:40 pm
Trusted Member
Posted by: @wouterv

Nice features! Maybe a warning during flashing would be nice though, not everybody knows that you brick your device if you turn off power while flashing.

Are you speaking generically, or with specific knowledge of the Buddy board?

Posted : 30/03/2020 2:29 pm

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