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Tutorials

Using M.2 Connectors for MicroMod Modules

Overview​

The SparkFun MicroMod ecosystem uses a standardized M.2 (NGFF) E-Key 67-pin connector (0.5mm pitch) to let you swap microcontroller "Processor Boards" into different peripheral "Carrier Boards" without soldering.

In this tutorial, we cover:

  1. How the MicroMod M.2 interface works mechanically and electrically.
  2. Standard pinout mappings across power, USB, UART, I2C, SPI, CAN, SDIO, and GPIO.
  3. How to define a reusable MicroMod M.2 67-pin connector component and footprint in tscircuit.
  4. How to wire a Carrier Board to a MicroMod Processor slot using <chip />, <smtpad />, <platedhole />, and <trace />.

1. The MicroMod M.2 Physical Interface​

Every MicroMod connection consists of three physical elements:

  • Processor Board: A 22mm × 22mm PCB with gold-plated M.2 edge fingers (beveled card edge) and an E-Key notch between pins 24 and 31.
  • Carrier Board Connector: A 67-pin SMD M.2 E-Key female socket (typically 4.2mm height, 0.5mm pin pitch) mounted on the Carrier Board.
  • M2.5 Phillips Standoff & Screw: Located 18mm from the connector origin to hold the Processor Board flat against the spring contacts.

Odd vs. Even Pin Numbering​

On the M.2 socket:

  • Odd pins (1, 3, 5, ..., 75) correspond to the top row of edge contacts on the Processor Board.
  • Even pins (2, 4, 6, ..., 74) correspond to the bottom row of edge contacts on the Processor Board.
  • Pins 24–31 are omitted to form the physical E-Key mechanical polarization notch, preventing reversed insertion.

2. Standard MicroMod v1.0 Pinout Reference​

To ensure any MicroMod Processor (ESP32, RP2040, STM32, Teensy, nRF52840, etc.) works seamlessly in any Carrier Board, SparkFun standardizes the 67 pins into functional groups:

Bus / GroupM.2 Pin NumbersPrimary SignalsDescription
Power & Battery2, 43.3VMain regulated 3.3V supply rail (up to 1A)
Input / USB Power74 (VIN), 70 (USB_VIN)5V / VINCarrier input supply & USB VBUS monitor
Backup Battery6BATT_VIN / RTC_3VCoin-cell or LiPo backup for RTC
Ground (GND)1, 7, 23, 33, 39, 59, 69, 75GNDDistributed return and signal shield grounds
Control & Boot5 (RESET#), 73 (BOOT), 3 (3.3V_EN)System ControlActive-low reset, bootloader entry, and regulator enable
USB (Device/Host)17 (USB_D-), 19 (USB_D+), 21 (USBH_D-), 23Differential 90ΩNative USB enumeration and programming
UART (Serial)18 (TX1), 20 (RX1), 22 (RTS1), 32 (CTS1)Primary Hardware UARTHardware flow-controlled serial interface
Secondary UART34 (TX2), 36 (RX2)UART2Secondary peripheral serial port
I2C (Primary & Int)12 (SDA), 14 (SCL), 16 (I2C_INT#)Qwiic / I2C BusPrimary I2C bus (typically pulled up to 3.3V via 2.2kΩ–4.7kΩ)
I2C1 (Split)50 (SDA1), 52 (SCL1)Secondary I2CDedicated secondary I2C bus
Primary SPI55 (CS), 57 (SCK), 59 (GND), 61 (COPI), 63 (CIPO)High-Speed SPIFlash/display/sensor SPI bus
SDIO / SPI160, 62, 64, 66, 68, 72SDIO_SCK/CMD/DATA0-34-bit SD card interface or secondary SPI
Audio / I2S / PDM41, 43, 45, 47, 49AUD_MCLK/OUT/IN/LRCLK/BCLKDigital audio I2S and PDM microphone bus
Analog (ADC)38 (A0), 35 (A1), 4 (BATT_MEAS/3)Analog Inputs0–3.3V ADC inputs
PWM42 (PWM0), 44 (PWM1)Dedicated PWMTimer-backed PWM channels
Digital GPIO40 (D0), 42 (D1), 10, 18, 20, 32, 34, 36, 38G0 – G11General-purpose digital I/O

3. Creating a MicroMod M.2 Carrier Connector in tscircuit​

When designing a Carrier Board in tscircuit, you can wrap the M.2 E-Key socket footprint and pin labels into a reusable component:

MicroModConnector.tsx
const MICROMOD_PIN_LABELS = {
  pin1: ["GND1"],
  pin2: ["V3_3_1"],
  pin3: ["EN_3V3"],
  pin4: ["V3_3_2"],
  pin5: ["RESET_N"],
  pin6: ["RTC_3V"],
  pin12: ["I2C_SDA"],
  pin14: ["I2C_SCL"],
  pin16: ["I2C_INT_N"],
  pin17: ["USB_DM"],
  pin18: ["UART_TX1"],
  pin19: ["USB_DP"],
  pin20: ["UART_RX1"],
  pin38: ["ADC0"],
  pin40: ["D0"],
  pin42: ["PWM0"],
  pin55: ["SPI_CS"],
  pin57: ["SPI_SCK"],
  pin61: ["SPI_COPI"],
  pin63: ["SPI_CIPO"],
  pin73: ["BOOT"],
  pin75: ["GND2"],
} as const

export const MicroModM2Connector = ({
  name,
  pcbX = 0,
  pcbY = 0,
}: {
  name: string
  pcbX?: number
  pcbY?: number
}) => (
  <chip
    name={name}
    pcbX={pcbX}
    pcbY={pcbY}
    pinLabels={MICROMOD_PIN_LABELS}
    footprint={
      <footprint>
        {/* 67-pin 0.5mm pitch SMD row + mechanical mounting bosses */}
        {Array.from({ length: 38 }).map((_, idx) => {
          const pinNum = idx * 2 + 1
          // Skip E-Key notch (pins 24..31)
          if (pinNum >= 25 && pinNum <= 31) return null
          const xOffset = (idx - 18.5) * 0.5
          return (
            <smtpad
              key={`odd-${pinNum}`}
              portHints={[`pin${pinNum}`]}
              shape="rect"
              pcbX={`${xOffset}mm`}
              pcbY="0mm"
              width="0.28mm"
              height="1.15mm"
            />
          )
        })}
        {/* M2.5 Standoff Mounting Hole 18mm from connector edge */}
        <platedhole
          portHints={["MOUNT_GND"]}
          pcbX="0mm"
          pcbY="18mm"
          holeDiameter="2.7mm"
          outerDiameter="5.0mm"
        />
      </footprint>
    }
  />
)

4. Wiring a Complete MicroMod Carrier Board Circuit​

Below is an example Carrier Board that wires a MicroMod M.2 Socket (U1) to:

  • Bypass decoupling capacitors (C1, C2) on the 3.3V rail,
  • Pull-up resistors (R1, R2) on the primary I2C (SDA/SCL) bus,
  • A status LED (D1 + R3) driven by D0.
micromod-carrier-board.tsx
import { MicroModM2Connector } from "./MicroModConnector"

export const MicroModCarrierBoard = () => (
  <board width="45mm" height="45mm" centerX={0} centerY={8}>
    <MicroModM2Connector name="U1" pcbX={0} pcbY={0} />

    {/* 3.3V Rail Decoupling */}
    <capacitor
      name="C1"
      capacitance="10uF"
      footprint="0603"
      pcbX={-12}
      pcbY={2}
    />
    <capacitor
      name="C2"
      capacitance="100nF"
      footprint="0402"
      pcbX={-12}
      pcbY={5}
    />

    {/* I2C Pull-Up Resistors (4.7k to 3.3V) */}
    <resistor
      name="R1"
      resistance="4.7k"
      footprint="0402"
      pcbX={12}
      pcbY={2}
    />
    <resistor
      name="R2"
      resistance="4.7k"
      footprint="0402"
      pcbX={12}
      pcbY={5}
    />

    {/* Status LED on D0 */}
    <resistor
      name="R3"
      resistance="1k"
      footprint="0603"
      pcbX={14}
      pcbY={12}
    />
    <led name="D1" footprint="0603" pcbX={14} pcbY={16} />

    {/* Power & Decoupling Traces */}
    <trace from=".U1 > .V3_3_1" to=".C1 > .pos" />
    <trace from=".C1 > .pos" to=".C2 > .pos" />
    <trace from=".U1 > .GND1" to=".C1 > .neg" />
    <trace from=".C1 > .neg" to=".C2 > .neg" />

    {/* I2C Pull-ups */}
    <trace from=".U1 > .I2C_SDA" to=".R1 > .pin1" />
    <trace from=".U1 > .I2C_SCL" to=".R2 > .pin1" />
    <trace from=".R1 > .pin2" to=".U1 > .V3_3_1" />
    <trace from=".R2 > .pin2" to=".U1 > .V3_3_1" />

    {/* Status LED Wiring */}
    <trace from=".U1 > .D0" to=".R3 > .pin1" />
    <trace from=".R3 > .pin2" to=".D1 > .pos" />
    <trace from=".D1 > .neg" to=".U1 > .GND2" />
  </board>
)

5. Layout & Design Best Practices​

  1. Keep-Out Zone Under the Processor Board: The 22mm × 22mm area between the M.2 socket and the M2.5 standoff sits directly beneath the Processor Board. Avoid placing tall components (>1.5mm height) in this region on the Carrier Board.
  2. USB Differential Pair Routing: Route USB_DP (Pin 19) and USB_DM (Pin 17) as a 90Ω differential pair with minimal stub length and matched trace lengths.
  3. 3.3V Enable (3.3V_EN, Pin 3): Tie 3.3V_EN to your Carrier Board's 3.3V regulator EN pin with a 100kΩ pull-up to VIN so the processor or an external switch can power-cycle the 3.3V rail cleanly.
  4. References & Datasheets: