The MaKr Melzi 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 Rds100W) 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%.
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