This project provides a circuit design and PCB layout for the generic elements of an NMEA 2000 module based around the Teensy 4.0 microcontroller.
The PCB layout can be imported into other projects, relieving them of the effort of designing and implementing fundamental services which power, interface, configure and process most NMEA hardware devices. A project designer using the PCB layout can focus on just those elements of application design appropriate to their task in hand.
A parallel project pdjr-nmea2000-common-firmware provides a C++ pattern and associated libraries that can be used as a basis for implementing firmware which exploits this hardware.
The double-sided PCB is suitable for use in a *** case and employs both surface-mount and through-hole components.
The project supports both Teensy 3.2 and Teensy 4.0 microcontroller modules.
A TMR-2-2411 DC-DC converter takes bus power from NET-S/NET-C and outputs a 5VDC 400mA supply for the PCB.
The converter power supply input is protected by a 0.25A self-resetting polymer fuse selected on the assumption of a 12VDC bus voltage.
Output from the converter is filtered through a smooting capacitor.
An MCP-2551/IP CAN controller converts data on CAN-H/CAN-L to signals suitable for microcontroller use. The signals are level-shifted to 3.3VDC for compatability with the Teensy 4.0.
A switch switch-selectable 120 Ohm bus termination resistor allows the module to be used as either an NMEA drop or terminal node.
The configuration interface consists of an SPST momentary tactile switch (PRG) and an 8-position DIL switch (INSTANCE).
PRG is directly connected to GPIO D14 and is active low (GPIO D14 should be configured with INPUT_PULLUP).
INSTANCE channels are pulled low, active high, and connected to the parallel inputs of a PISO buffer interfaced through GPIO D10, D11 and D12.
The display interface consists of a single TRANSMIT_LED and up to 16 additional status LEDs for use by the host application.
TRANSMIT_LED is driven directly by GPIO D15.
The status LEDs are driven at 5VDC by a SIPO buffer with the buffer interface connected to GPIO D0, D1 and D2.
The PCB design is simply imported into a new KiCad project and then extended to provide the required application features.
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Open Kicad(1) and create a new project.
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Download MNEA2000-COMMON.kicad_pcb into the new project folder.
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Open pcbnew(1), choose FILE->MERGE, select the file you just downloaded and save it as a the new project's PCB (if your KiCad project is called blob.prj then save the file as blob.kicad_pcb).