GPIO Module

The GPIO module (General Purpose Input Output) is an additional, optional PCB that can be connected to the Original Prusa MK4/S, MK3.9/S, or MK3.5/S.

The module provides expanded functionality by allowing the control of external devices through connections to the GPIO board pins, which can operate in either INPUT or OUTPUT mode. This versatility opens up a wide range of potential use cases.

Share and discuss your projects with the other members of the Prusa Community on our official forum. We have created a dedicated GPIO section.

Use-case ideas

The module can control a camera shutter at a precise moment, making it ideal for creating visually perfect time-lapses, where each picture is captured at the exact same point in time.

Beyond controlling a camera shutter, the module can be used for various other applications. For example, it can trigger external lighting to illuminate the print area at specific stages of the printing process, ensuring optimal lighting conditions for quality checks or photography. Additionally, it can be configured to activate cooling fans or other peripheral devices, such as extractors or alarms, based on custom G-Code execution during prints, helping maintain optimal operating conditions and improving the safety and efficiency of the 3D printing environment.

Another powerful use case is the integration of a macro keyboard, where each keypress can trigger the execution of specific G-Code commands. This setup allows for rapid manual control of the printer's functions, such as starting or pausing a print, adjusting temperatures, or moving the print head to an exact position. The ability to trigger custom actions with a simple keypress can significantly streamline workflows, making the GPIO expansion module a versatile and indispensable tool for those looking to fully customize and optimize their 3D printing setup.

Safety first! 

While the ability to trigger G-Code via GPIO inputs adds great flexibility, it also comes with limitations and potential risks. Improper use or poorly timed G-Code commands can interfere with the printing process, leading to print failures or even damage to the printer. It’s crucial to thoroughly test any custom G-Code setups in a controlled environment before deploying them in actual print jobs to avoid unintended consequences.

Schematics 

The schematics are open source, and available on our page Open Source at Prusa Research. 

How to install the GPIO board

1. Ensure the printer is cooled down to room temperature, and switch it off.
2. Open the xBuddy box cover by removing four M3x6 screws.
   
   
3. Connect the GPIO cable to the I2C port.
   
   
4. Close the xBuddy box cover.
5. Ensure that the GPIO does not touch any metal parts of the xBuddy box or its cover. 
6. Enjoy your project!

Pins

The board features 8 pins, numbered 0-7. Pins 0-3 can be used as output, and pins 4-7 can function as either input or output. Each pin is of the open-drain type when used as an output, meaning it is controlled by a transistor that connects the pin to the ground (0 V) when active. When the pin is inactive, it remains "floating", which means it is not connected to any specific voltage, but due to internal pull-up resistors, the voltage on the pin can hover around 3.3 V. 

The behavior of the pins in an open-drain state when used as outputs can be explained as follows:

• Pin set to 0 (LOW): The pin is turned off and is in a "floating" state, which means it is not connected to any specific voltage. In this state, the voltage on the pin can fluctuate and is not well-defined unless stabilized by a pull-up resistor.

This "floating" state may cause the pin to pick up random electrical noise or interference, leading to unintended behavior if not properly managed. 

• Pin set to 1 (HIGH): The pin is turned on and connected to the ground (0 V), causing the voltage on the pin to drop to 0 V. This state is clear and does not lead to any ambiguity in signal detection.

When the pins are used as inputs, they can detect the voltage level applied to them. The input state is influenced by the presence of pull-up resistors, which can help ensure a consistently high voltage (3.3 V) when no other voltage source is applied.

Pull-up resistors

The board allows the connection of external pull-up resistors via solder jumpers labeled JP4 to JP7. These solder jumpers are located in the center of the board and are connected to the corresponding pins:

• JP4 is connected to Pin 4
• JP5 is connected to Pin 5
• JP6 is connected to Pin 6
• JP7 is connected to Pin 7

Solder jumpers JP7 to JP4 can be used to connect integrated pull-up resistors, which ensures that the pins remain at a high voltage (3.3 V) when not actively driven low by an external source or by the pin's output state. These pull-up resistors have a value of 10K ohms, which is a standard value to provide stable voltage without excessive current draw. If no resistor is connected to the solder jumper, the pin may remain in a floating state, potentially leading to unstable behavior. JP stands for "jumper," and if no resistor is connected, it creates no resistance.

For less experienced users, it's important to understand that open-drain outputs do not inherently produce a high voltage (3.3 V) but rather allow a connection to ground (0 V). Pull-up resistors are necessary to ensure that the pin remains at a high voltage when turned off or when used as an input. If not properly managed, a "floating" voltage can cause the pin to pick up electrical noise, leading to unwanted switching or system instability.

Setting GPIO via Custom G-Code

General Information

The following is a sequence of custom G-Code commands used for controlling the GPIO board. This allows you to configure output states, read input states, and manage other advanced settings on the board through G-Code instructions, integrating them seamlessly with your 3D printer’s workflow.

Pin control via G-Code

To control the output pins on the GPIO board, you can use the following G-Code commands:

1. Set Pin Mode (Output or Input)
M262 P B
   • P<0-7>: Select the pin number to configure (from 0 to 7).
   • B<0 or 1>: Set the pin mode.
     • 0 - configures the pin as an output
     • 1 - configures it as an input.
   • Example: M262 P0 B0 - Configures pin 0 as an output pin.
      
2. Write state to an Output Pin
   M264 P B<0 or 1>
   • P<0-7>: Select the pin number to write to (from 0 to 7).
   • B<0 or 1>: Write 0 to set the pin to LOW, or 1 to set the pin to HIGH.
   • Example: M264 P0 B1 - Sets output pin 0 to HIGH (1).
      
3. Toggle state of Output Pin
   M265 P
   • P<0-7>: Select the pin number to toggle (from 0 to 7).
   • This command flips the current state of the selected pin.
   • Example: M265 P0 - Toggles pin 0.
      
4. Advanced Register Setup (For Experienced Users)
   M267 R<1-3> B<0-255>
   • R<1-3>: Select the register to configure:
     • 1: Output Register.
     • 2: Polarity Register.
     • 3: Configuration Register.
   • B<0-255>: Set the value to be written to the selected register.
   • Example: M267 R3 B255 - Configures the Configuration Register with the value 255 (all pins set to inputs).

To read the state of pins or set up configurations, use the following G-Code commands:

1. Read state of Pin
   M263 P
   • P<0-7>: Select the pin number to read from (from 0 to 7).
   • The returned value will indicate whether the pin is HIGH (1) or LOW (0).
   • Example: M263 P6 - Reads the state of pin 6 (returns 32 for HIGH or 0 for LOW).
      
2. Read Entire Input Register
   M261 A B S