Building a MicroMod Carrier Board
Overview
SparkFun MicroMod processor boards use a 75-pin M.2 edge connector so that the processor module can plug into different carrier boards. A carrier board usually provides the regulated 3.3 V rail, ground return, reset and boot controls, and breakouts for buses such as I2C, SPI, UART, SWD, PWM, and analog inputs.
This tutorial shows a reusable tscircuit pattern for documenting a MicroMod carrier schematic. It intentionally focuses on the connector and signal mapping; before fabricating a real board, confirm the exact connector footprint, keepout, and mechanical dimensions against the MicroMod processor board and connector datasheets.
Start with the MicroMod M.2 socket
Use <connector /> with standard="m2" and add explicit labels for the pins
you plan to route. The example below labels the most common carrier-board
signals from the MicroMod v1.0 pinout and leaves unused keyed or secondary
signals unconnected.
Add carrier-board power
MicroMod signals are 3.3 V compatible. Do not connect processor GPIO or bus signals directly to 5 V logic. The carrier board should provide a clean 3.3 V rail, local bulk capacitance, and small decoupling capacitors close to the connector power pins. If your carrier accepts USB or battery input, model that power path separately and feed the connector from the regulated rail.
Break out common buses
Carrier boards usually expose a small set of MicroMod signals rather than every
pin. I2C is a good default because MicroMod defines I2C_SDA and I2C_SCL as
open-drain signals that need pull-up resistors on the carrier board. UART, SPI,
SWD, reset, and boot are common debugging and expansion connections.
Layout checklist
- Use the MicroMod connector drawing for pad geometry, key position, insertion direction, and board-edge keepout.
- Keep local 100 nF decoupling close to the 3.3 V and ground connector pins, and add enough bulk capacitance for the processor board and any carrier peripherals.
- Treat all exposed bus pins as 3.3 V logic unless a processor-board datasheet explicitly says otherwise.
- Put I2C pull-ups on the carrier board. Start with 4.7 kOhm for short traces and adjust for bus capacitance and target speed.
- Route USB and high-speed interfaces as controlled, short, matched differential paths when you use them.
- Mark intentionally unused MicroMod pins as no-connects in your design notes so future carrier-board revisions do not route them by accident.