Special offer: Save money by purchasing the full kit with this MaKr Melzi board, four motor driver modules and the MaKr graphical LCD panel.
- 128kB flash memory instead of the commonly used 64kB
- Screw terminals for all electrical connections – no crimping or soldering required
- Additional solder pads to allow addition of 2.54mm Molex connectors
- Full support for dual Z-axis designs like the Prusa Mendel – pads for two parallel connectors for the Z-Axis
- Power outputs can be used as direct spindle and pump drives for CNC applications
- Comes with 4 pluggable standard motor driver modules, easily exchangeable
- Nearly lossless reverse power protection, with no heatsink required
- No heatsinks required for the power outputs, even at full load
- USB-UART converter based on Microchip MCP2200 – offers up to 8 software controllable GPIO pins
- Modification- and extension-friendly PCB design despite being based on SMT technology – all relevant internal signals are accessible at solder pads with standard 2.54mm pitch
- Extensive documentation on the silkscreen – all connectors, jumper and pads are clearly marked (see product images above)
- Switched DC/DC converter for 5V generation
- Improved EMC protection for the microSD slot and the USB connection
- Designed from the ground up with the requirements of mass production in mind, resulting in a lower sales price
- One MaKr Melzi controller board, fully-assembled and tested.
- Four A4988 motor driver modules, fully-assembled with pin headers and tested
Please note: Neither a microSD card nor a Mini-USB cable is included. To connect the board to your PC you will need an additional Mini-USB cable. For printing from SD card you will need a microSD card (card must support SPI mode).
The full story
This board is built around an ATmega1284P MCU instead of the ATmega644P. Since current versions of the popular Marlin firmware already need about 60kB of memory it’s likely that future versions with added features will soon outgrow the current generation of ATmega644-based board designs. Even with the current versions, more than 64kB is already required to take full advantage of the possibilities of graphical displays.
Thanks to the provided screw terminals, wiring this controller board to the printer doesn’t require more than a screwdriver and a few minutes of time. However, the board is still highly- modifiable and extendable for anybody with some background in electronics. All important signals are accessible on solder pads in a 2.54mm pitch, well-documented right on the PCB. (see images above)
The power outputs feature free-wheeling diodes, allowing for PWM control of inductive loads. They are capable of directly driving DC spindle motors and coolant pumps in CNC applications. With appropriate software support, the analog inputs can be used to monitor the rotary speed, allowing for full closed-loop spindle control.
In order to reduce the power losses and the amount of heat generated, an efficient DC/DC converter is used for generating the required 5V power from the motor supply voltage. This removes the need for the selectable power resistor in the original Melzi design and makes it easier to use.
The USB-UART interface is based on a MCP2200 chip from Microchip. It offers up to 8 GPIO lines that can be accessed via USB and might be useful for some creative extensions. Drivers for the GPIO functions are available for Windows and for Linux as well.
Due to the high currents involved, most other designs don’t have any DC input power protection at all. Not having a reverse power protection means a very good chance of killing not only the controller electronics but in the worst case even a connected PC via the USB cable. A simple protection diode is not applicable for such high currents, as at 15A it would burn almost 12W, requiring a large heat sink on its own. Instead, a special, almost lossless PMOS transistor with Rds<8 milliohm is used for this design.
For the power outputs a carefully selected NMOS transistor with a very low Rds value is used. This guarantees minimal power losses even at high currents of up to 10A. All high current areas of the PCB and all components related to high currents (DC input connectors, fuse, polarity protection, power MOSFETs and output connectors) will get hot, but they are designed for a rather high thermal load. When used without a housing, no heatsink is required. However, if used in a closed housing, additional cooling measures (like a small fan to ensure some air flow) might be necessary.
When using high-power heatbeds (>100W) the use of PWM-controlled slowed-down heat-up modes and/or supply voltages higher than 12V is highly recommended. At 24V supply voltage all power losses on the board will be not only 1/2, but 1/4 of the losses at 12V. Additionally, the motors perform better at higher voltages and allow for faster movements. When using a 12V fan at 24V please ensure that the maximum PWM output is set to 50%.