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SparkFun microSD Transflash Breakout - ESP32-C5 Wiring Guide

Overview

This guide shows how to connect the SparkFun microSD Transflash Breakout board to the ESP32-C5 DevKit. ESP32-C5 does not support SDMMC/SDIO host, so the firmware uses SPI mode for SD card access.

If you also have a GPS module (e.g. GT-U7): J1 Pin 1 (3.3V) and Pin 15 (GND) must each use a Y-cable (or splice) so one leg goes to the SD breakout and one to the GPS — both devices share the same 3.3V and GND from the ESP32-C5.

Required Connections (SPI mode)

VCC (3.3V)
GND (Ground)
CLK (SPI SCLK)
DI (SPI MOSI - Data In to card)
DO (SPI MISO - Data Out from card)
CS (Chip Select)
CD (Card Detect, optional)

Wiring Table (SPI Mode)

SparkFun Label	ESP32-C5 Pin	Header Location	GPIO Number	Function
VCC	Pin 1	J1 (Left Side)	3V3	Power
GND	Pin 15	J1 (Left Side)	GND	Ground
SCK	Pin 10	J1 (Left Side)	GPIO9	SPI_CLK
DI	Pin 11	J1 (Left Side)	GPIO10	SPI_MOSI
DO	Pin 9	J1 (Left Side)	GPIO8	SPI_MISO
CS	Pin 8	J1 (Left Side)	GPIO7	SPI_CS
CD	Pin 12	J1 (Left Side)	GPIO26	Card Detect (Input Pull-up)

Note: If your SparkFun breakout does not expose CS, some breakouts tie CS to GND (always selected). The firmware expects CS on GPIO7.

Wiring Diagram (SD only)

  ┌─────────────────────────────┐         ┌──────────────────────────────┐
  │  SparkFun microSD Breakout  │         │   ESP32-C5 DevKit (J1)        │
  │                             │         │                               │
  │   VCC ──────────────────────┼─────────┼─► Pin 1  (3V3)               │
  │   GND ──────────────────────┼─────────┼─► Pin 15 (GND)               │
  │   SCK ──────────────────────┼─────────┼─► Pin 10 (GPIO9)  CLK        │
  │   DI  ──────────────────────┼─────────┼─► Pin 11 (GPIO10) MOSI       │
  │   DO  ──────────────────────┼─────────┼─► Pin 9  (GPIO8)  MISO       │
  │   CS  ──────────────────────┼─────────┼─► Pin 8  (GPIO7)  Chip Select│
  │   CD  ──────────────────────┼─────────┼─► Pin 12 (GPIO26) Card Detect│
  │                             │         │      (optional)               │
  └─────────────────────────────┘         └──────────────────────────────┘

Combined Pin Diagram (SD Card + GPS)

When using both the SparkFun microSD breakout and a GPS module (e.g. GT-U7 / NEO-6M), power and ground are shared:

J1 Pin 1 (3.3V) and J1 Pin 15 (GND) each need a Y-cable (or one 3.3V and one GND split): one branch to the SD breakout, one branch to the GPS. Do not rely on a single wire to the first device and then daisy‑chain to the second; use a proper Y (or star) so both get a direct connection to 3.3V and GND.

                    ESP32-C5 DevKit J1 (left) + J3 (right)
  ┌─────────────────────────────────────────────────────────────────────────┐
  │  Pin 1:  3V3  ◄────── Y-cable ──────┬────► SD Breakout VCC              │
  │                                     └────► GPS VCC                      │
  │  Pin 2:  RST   (do not connect)                                          │
  │  Pin 3:  GPIO2 (strapping – do not use)                                  │
  │  Pin 4:  GPIO3 (strapping – do not use)                                  │
  │  Pin 5:  GPIO0                                                           │
  │  Pin 6:  GPIO1  ◄──────────────────────── GPS PPS (optional)            │
  │  Pin 7:  GPIO6                                                           │
  │  Pin 8:  GPIO7  ◄──────────────────────── SD CS                         │
  │  Pin 9:  GPIO8  ◄──────────────────────── SD MISO (DO)                   │
  │  Pin 10: GPIO9  ◄──────────────────────── SD CLK (SCK)                   │
  │  Pin 11: GPIO10 ◄──────────────────────── SD MOSI (DI)                   │
  │  Pin 12: GPIO26 ◄──────────────────────── SD CD (optional)              │
  │  Pin 13: GPIO25 ◄──────────────────────── GPS PPS (alt; if not using 6)  │
  │  Pin 14: 5V     (do NOT use – would damage SD/GPS)                       │
  │  Pin 15: GND    ◄────── Y-cable ──────┬────► SD Breakout GND            │
  │                                       └────► GPS GND                    │
  └─────────────────────────────────────────────────────────────────────────┘
  ┌─────────────────────────────────────────────────────────────────────────┐
  │  J3 (right):  Pin 4 = GPIO24 (TX) ◄────── GPS RXD (optional)            │
  │               Pin 5 = GPIO23 (RX) ◄────── GPS TXD (NMEA from GPS)        │
  └─────────────────────────────────────────────────────────────────────────┘

Summary: Use Y-cables (or equivalent) on 3.3V (Pin 1) and GND (Pin 15) so the SD card and GPS each have their own lead from the ESP32-C5. Same 3.3V and GND rail, two physical wires per net.

Quick Wiring Reference

SparkFun microSD Breakout → ESP32-C5 DevKit

1. VCC   →  J1 Pin 1  (3V3)      [Left side, top; use Y-cable if also powering GPS]
2. GND   →  J1 Pin 15 (GND)      [Left side, bottom; use Y-cable if also powering GPS]
3. SCK   →  J1 Pin 10 (GPIO9)    SPI_CLK
4. DI    →  J1 Pin 11 (GPIO10)   SPI_MOSI
5. DO    →  J1 Pin 9  (GPIO8)    SPI_MISO
6. CS    →  J1 Pin 8  (GPIO7)    SPI_CS
7. CD    →  J1 Pin 12 (GPIO26)   Card Detect (optional)

Card Detect (CD) Logic

LOW (0V): Card is Inserted (default: CONFIG_SD_CD_ACTIVE_LOW=y)
HIGH (3.3V): Card is Removed (pin floats high with pull-up)

If your breakout uses inverted logic (HIGH = inserted), run idf.py menuconfig → ESP32 iperf Configuration → SD Card → uncheck Card Detect: LOW = inserted.

Breakout doesn’t support CD: Some SparkFun-style breakouts have a CD pad or through-hole that is not connected to the slot’s card-detect switch (the slot may not have a CD pin). If wiring is correct but status always shows REMOVED (or CD never changes), disable CD: idf.py menuconfig → ESP32 iperf Configuration → SD Card → set Card Detect GPIO to -1. The card will still mount and work; only insert/remove detection is disabled.

Pin Locations on ESP32-C5 DevKit

J1 (LEFT SIDE - Top to Bottom):

Pin 1:  3V3     ← VCC
Pin 2:  RST     (Reset - do not connect)
Pin 3:  GPIO2   (Strapping - do not use)
Pin 4:  GPIO3   (Strapping - do not use)
Pin 5:  GPIO0
Pin 6:  GPIO1   (GPS PPS - if used)
Pin 7:  GPIO6
Pin 8:  GPIO7   ← CS
Pin 9:  GPIO8   ← MISO (DO)
Pin 10: GPIO9   ← CLK (SCK)
Pin 11: GPIO10  ← MOSI (DI)
Pin 12: GPIO26  ← CD (optional)
Pin 13: GPIO25  (GPS PPS - if used)
Pin 14: 5V      (do not use - too high voltage)
Pin 15: GND     ← GND
Pin 16: NC      (No connection)

Important Notes

⚠️ Warnings:

Use 3.3V ONLY - Do NOT connect to 5V (Pin 14) - this will damage the microSD card!
ESP32-C5 does not have SDMMC host; SPI mode is required
CD is optional: LOW = inserted, HIGH = removed (with pull-up)

Current Configuration

The firmware is configured for SPI mode using:

CLK: GPIO9
MOSI: GPIO10
MISO: GPIO8
CS: GPIO7
CD: GPIO26 (optional)

Testing

After wiring, the firmware will automatically detect the SD card on boot. You should see:

I (xxx) sd_card: Initializing SD card via SPI...
I (xxx) sd_card: SD card mounted successfully at /sdcard
I (xxx) sd_card: SD card ready: XX.XX MB total, XX.XX MB free

If the card is not detected, check:

All connections are secure
Card is properly inserted in the breakout board
Card is formatted (FAT32)
Power supply is stable (3.3V)

Troubleshooting

Card not detected:

Verify VCC is connected to 3V3 (Pin 1), NOT 5V
Check GND connection
Ensure card is properly seated in the breakout board
Try a different microSD card

Initialization fails:

Card may need formatting (FAT32)
Check for loose connections
Verify GPIO pins are correct
Some cards may not work in SPI mode - try a different brand

File system errors:

Card may be corrupted - reformat as FAT32
Check card capacity (very large cards may have issues)
Ensure proper power supply

CD always shows REMOVED but card works:

Your breakout or slot may not support Card Detect (CD pad may be unconnected). Disable CD: menuconfig → ESP32 iperf Configuration → SD Card → Card Detect GPIO = -1.

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