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esp32-dev/components/common-devices.md
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suyushi 5700eb4115 Initial: knowledge base
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Common Devices Reference

类别：reference | 主题：常用器件与模块速查 | 信源： 多平台汇总

Cross-platform device/module reference for Raspberry Pi and ESP32 GPIO configuration. Used to determine pin requirements, I2C addresses, voltage levels, and platform-specific wiring guidance.

Table of Contents

Category 1: Sensors — Environmental

BME280 (Temperature/Humidity/Pressure)

  • Interface：I2C (default), SPI
  • Required Pins：I2C: SDA, SCL. SPI: MOSI, MISO, SCLK, CS
  • I2C Address：0x76 (SDO→GND), 0x77 (SDO→VDD)
  • Voltage：1.8–3.6V (most breakouts accept 3.3V or 5V input)
  • Pull-ups：Provided on most breakouts

RPi Notes:

  • Use I2C1 (GPIO2 SDA, GPIO3 SCL)
  • Enable with dtparam=i2c_arm=on
  • SPI mode: SPI0 (GPIO10 MOSI, GPIO9 MISO, GPIO11 SCLK, GPIO8 CE0)

ESP32 Notes:

  • Any GPIO pair for I2C via GPIO matrix
  • Default Wire library: GPIO21 SDA, GPIO22 SCL
  • SPI VSPI default: GPIO23 MOSI, GPIO19 MISO, GPIO18 SCLK, GPIO5 CS

Gotchas:

  • ADDRESS COLLISION with BMP280 — both use 0x76/0x77
  • Cannot use BME280 + BMP280 on same I2C bus unless one is on alternate address
  • Use I2C multiplexer (TCA9548A) if both needed at same address

BMP280 (Temperature/Pressure — no humidity)

  • Interface：I2C (default), SPI
  • Required Pins：I2C: SDA, SCL. SPI: MOSI, MISO, SCLK, CS
  • I2C Address：0x76 (SDO→GND), 0x77 (SDO→VDD)
  • Voltage：1.8–3.6V (most breakouts accept 3.3V or 5V input)
  • Pull-ups：Provided on most breakouts

RPi Notes:

  • Use I2C1 (GPIO2 SDA, GPIO3 SCL)
  • Enable with dtparam=i2c_arm=on
  • SPI mode: SPI0 (GPIO10 MOSI, GPIO9 MISO, GPIO11 SCLK, GPIO8 CE0)

ESP32 Notes:

  • Any GPIO pair for I2C via GPIO matrix
  • Default Wire library: GPIO21 SDA, GPIO22 SCL
  • SPI VSPI default: GPIO23 MOSI, GPIO19 MISO, GPIO18 SCLK, GPIO5 CS

Gotchas:

  • ADDRESS COLLISION with BME280
  • Registers are mostly compatible but not identical — don't assume BME280 libraries work on BMP280
  • Cheap clone boards sometimes mislabel BMP280 as BME280

DHT22 / AM2302 (Temperature/Humidity)

  • Interface：Single-wire proprietary protocol (NOT 1-Wire/Dallas)
  • Required Pins：DATA (1 GPIO)
  • I2C Address：N/A
  • Voltage：3.3V–5V (data pin is 3.3V logic compatible)
  • Pull-ups：4.7kΩ–10kΩ on data line (some breakouts include it)

RPi Notes:

  • Use any available GPIO
  • No overlay needed
  • Timing-sensitive — occasional read failures are normal; retry in software
  • Minimum 2-second sampling interval (do not exceed 0.5 Hz)

ESP32 Notes:

  • Use any GPIO
  • Avoid strapping pins (GPIO0, 2, 5, 12, 15)
  • Avoid input-only pins (GPIO34-39) — data pin is bidirectional

Gotchas:

  • THIS IS NOT 1-Wire PROTOCOL — do not use w1-gpio overlay
  • Do not confuse with DS18B20
  • Requires specific library (e.g., Adafruit DHT library)
  • DHT11 is the cheaper/less accurate variant — same protocol

DS18B20 (Temperature, 1-Wire)

  • Interface：1-Wire (Dallas protocol)
  • Required Pins：DQ (data, 1 GPIO)
  • I2C Address：N/A
  • Voltage：3.0–5.5V (supports parasitic power: data + GND only)
  • Pull-ups：4.7kΩ required on data line

RPi Notes:

  • Default: GPIO4 with dtoverlay=w1-gpio
  • Custom pin: dtoverlay=w1-gpio,gpiopin=N
  • Parasitic power: dtoverlay=w1-gpio-pullup,gpiopin=N
  • Multiple sensors can share one data pin (each has unique 64-bit address)

ESP32 Notes:

  • Any GPIO via OneWire library
  • Avoid strapping pins
  • Avoid input-only pins (GPIO34-39)

Gotchas:

  • Multiple sensors on one bus is a key feature — each has factory-programmed unique ID
  • Parasitic power mode can cause issues with cable runs >3m
  • Counterfeit DS18B20s are common — may have worse accuracy or fail parasitic power

SHT31 (Temperature/Humidity)

  • Interface：I2C
  • Required Pins：SDA, SCL. Optional: ALERT (interrupt), RST (active-low reset)
  • I2C Address：0x44 (ADDR→GND), 0x45 (ADDR→VDD)
  • Voltage：2.4–5.5V (most breakouts have regulator)
  • Pull-ups：Provided on most breakouts

RPi Notes:

  • Use I2C1 (GPIO2 SDA, GPIO3 SCL)
  • Enable with dtparam=i2c_arm=on

ESP32 Notes:

  • Any GPIO pair for I2C via GPIO matrix

Gotchas:

  • ADDRESS COLLISION — INA219 also uses 0x44/0x45
  • Has built-in heater element for self-diagnostics (enable via register)
  • Higher accuracy than DHT22

Category 2: Sensors — Motion/Position

MPU6050 (6-Axis IMU — Accelerometer + Gyroscope)

  • Interface：I2C
  • Required Pins：SDA, SCL. Optional: INT (interrupt — recommended for DMP)
  • I2C Address：0x68 (AD0→GND), 0x69 (AD0→VDD)
  • Voltage：3.3V (VDD). Most breakouts accept 3.3V–5V input
  • Pull-ups：Provided on most breakouts

RPi Notes:

  • Use I2C1 (GPIO2/3)
  • Connect INT to any GPIO if using interrupt-driven reads
  • No specific overlay needed beyond dtparam=i2c_arm=on

ESP32 Notes:

  • Any GPIO pair for I2C
  • Connect INT to any input-capable GPIO
  • Input-only pins (GPIO34-39) are fine for INT output

Gotchas:

  • ADDRESS COLLISION — 0x68 collides with DS3231 RTC
  • If using both, put one on alternate address or use I2C multiplexer
  • Has built-in DMP (Digital Motion Processor) — use INT pin for DMP-ready interrupts
  • MPU9250 is the 9-axis successor (adds magnetometer) — same I2C address scheme

ADXL345 (3-Axis Accelerometer)

  • Interface：I2C, SPI
  • Required Pins：I2C: SDA, SCL. SPI: MOSI, MISO, SCLK, CS. Optional: INT1, INT2
  • I2C Address：0x53 (ALT ADDRESS/SDO→GND), 0x1D (ALT ADDRESS/SDO→VDD)
  • Voltage：2.0–3.6V (most breakouts accept 3.3V–5V)
  • Pull-ups：Provided on most breakouts

RPi Notes:

  • I2C1 (GPIO2/3) or SPI0 (GPIO7-11)
  • Interrupt pins to any available GPIO

ESP32 Notes:

  • Any GPIO pair for I2C, any pins for SPI via GPIO matrix
  • Avoid flash pins (GPIO6-11) for SPI

Gotchas:

  • Default I2C address 0x53 is uncommon in collisions
  • SPI mode is activated by pulling CS low — if CS is floating, chip may not respond on I2C
  • Has configurable tap detection, freefall detection, and activity/inactivity interrupts

HMC5883L / QMC5883L (Magnetometer/Compass)

  • Interface：I2C
  • Required Pins：SDA, SCL. Optional: DRDY (data ready interrupt)
  • I2C Address：HMC5883L: 0x1E (fixed). QMC5883L: 0x0D (fixed)
  • Voltage：2.16–3.6V (most breakouts accept 3.3V–5V)
  • Pull-ups：Provided on most breakouts

RPi Notes:

  • I2C1 (GPIO2/3)
  • No special overlay

ESP32 Notes:

  • Any GPIO pair for I2C

Gotchas:

  • HMC5883L and QMC5883L have DIFFERENT I2C addresses and DIFFERENT register maps
  • They are NOT interchangeable in software
  • Many cheap "HMC5883L" boards actually contain QMC5883L chips — check chip marking
  • GY-271 boards may have either chip
  • Libraries must match the actual chip

NEO-6M / NEO-7M / NEO-M8N (GPS Module)

  • Interface：UART (primary), I2C (some models), SPI (some models)
  • Required Pins：UART: TX, RX. Optional: PPS (pulse-per-second for precision timing)
  • I2C Address：0x42 (when I2C interface is used, some modules only)
  • Voltage：2.7–3.6V (most breakouts accept 3.3V–5V)
  • Pull-ups：N/A for UART

RPi Notes:

  • UART0/PL011 on GPIO14 (TX) / GPIO15 (RX)
  • On Pi 3/4/Zero2W, Bluetooth uses PL011 — add dtoverlay=disable-bt or dtoverlay=miniuart-bt
  • On Pi 5, no BT conflict
  • For PPS: dtoverlay=pps-gpio,gpiopin=N
  • RPi TX → GPS RX, RPi RX → GPS TX (crossover)

ESP32 Notes:

  • Use UART1 or UART2 on any GPIO pair via GPIO matrix
  • UART0 is typically USB-serial debug — avoid reassigning
  • PPS to any input-capable GPIO

Gotchas:

  • Cold start can take 1-5 minutes to get a fix
  • Needs clear sky view for antenna
  • NMEA output at 9600 baud by default
  • PPS signal is critical for NTP servers or precision timing applications

Category 3: Sensors — Analog/Power

ADS1115 (16-bit ADC, 4-channel)

  • Interface：I2C
  • Required Pins：SDA, SCL. Optional: ALERT/RDY (interrupt/data-ready)
  • I2C Address：0x48 (ADDR→GND), 0x49 (ADDR→VDD), 0x4A (ADDR→SDA), 0x4B (ADDR→SCL)
  • Voltage：2.0–5.5V
  • Pull-ups：Provided on most breakouts

RPi Notes:

  • I2C1 (GPIO2/3)
  • Essential for RPi projects needing analog inputs — RPi has no built-in ADC
  • Enable with dtparam=i2c_arm=on

ESP32 Notes:

  • Any GPIO pair for I2C
  • Less commonly needed since ESP32 has built-in 12-bit ADC
  • Useful for higher resolution (16-bit) or to avoid ADC2/WiFi conflicts

Gotchas:

  • 0x48 address collides with TMP102 temperature sensor
  • Can run 4 devices on one I2C bus (4 addresses) for up to 16 analog channels
  • Programmable gain amplifier (PGA) allows measuring small voltages
  • Max sample rate is 860 SPS
  • ADS1015 is the cheaper 12-bit variant with same pinout and addresses

INA219 (Current/Voltage/Power Monitor)

  • Interface：I2C
  • Required Pins：SDA, SCL. Also: VIN+, VIN- (power sense pins, not GPIO)
  • I2C Address：0x40 (A0=GND,A1=GND), 0x41, 0x44, 0x45 (via A0/A1 pins)
  • Voltage：3.0–5.5V (bus voltage measurement up to 26V)
  • Pull-ups：Provided on most breakouts

RPi Notes:

  • I2C1 (GPIO2/3)

ESP32 Notes:

  • Any GPIO pair for I2C

Gotchas:

  • ADDRESS COLLISION — 0x40 collides with PCA9685 servo driver
  • 0x44/0x45 collide with SHT31
  • If using INA219 + PCA9685, must configure different addresses via A0/A1 pins
  • Shunt resistor value (typically 0.1Ω) determines current measurement range — must match library calibration

Category 4: Displays

SSD1306 (OLED Display, 128×64 or 128×32)

  • Interface：I2C (most common), SPI
  • Required Pins：I2C: SDA, SCL. SPI: MOSI, SCLK, CS, DC, RST (optional)
  • I2C Address：0x3C (common), 0x3D (alternate, set by resistor)
  • Voltage：3.3V–5V (most modules have regulator)
  • Pull-ups：Provided on most breakouts

RPi Notes:

  • I2C1 (GPIO2/3) for I2C mode
  • SPI0 for SPI mode
  • I2C mode fine for single display, SPI faster for animations

ESP32 Notes:

  • Any GPIO pair for I2C, any pins for SPI
  • SPI recommended for high refresh rate

Gotchas:

  • 0x3C address collides with SH1106 OLED (similar but different driver)
  • 128×32 variant usually has fixed 0x3C address
  • Some boards labeled "SSD1306" actually use SH1106 — different memory layout (132×64 with offset)

ST7789 (TFT Color Display, typically 240×240 or 240×320)

  • Interface：SPI only
  • Required Pins：MOSI, SCLK, CS, DC, RST, BL (backlight)
  • I2C Address：N/A
  • Voltage：3.3V logic. Most modules accept 3.3V–5V power
  • Pull-ups：N/A

RPi Notes:

  • SPI0 (GPIO10 MOSI, GPIO11 SCLK, GPIO8 CE0)
  • DC on any GPIO (commonly GPIO25)
  • RST on any GPIO (commonly GPIO27)
  • BL on PWM-capable GPIO (GPIO12 or GPIO18) for brightness control, or tie to 3.3V

ESP32 Notes:

  • VSPI or any pins via GPIO matrix
  • SPI clock can run up to 80MHz — good for smooth display updates

Gotchas:

  • SPI-only, no I2C option
  • ST7735 is the smaller cousin (128×160) — different driver, similar interface
  • Some displays omit CS pin (tied to GND) — prevents sharing SPI bus
  • BL pin may be active-high or active-low depending on module

HD44780 (Character LCD, 16×2 or 20×4, via PCF8574 I2C Backpack)

  • Interface：Parallel GPIO (6+ pins), I2C via PCF8574 backpack (recommended)
  • Required Pins：I2C: SDA, SCL. Direct: RS, EN, D4-D7 (4-bit = 6 GPIOs)
  • I2C Address：0x27 (most common), 0x3F (some variants). PCF8574A: 0x38–0x3F
  • Voltage：5V for LCD. I2C backpack tolerates 3.3V I2C signals
  • Pull-ups：Provided on PCF8574 backpack

RPi Notes:

  • Use I2C backpack to save GPIOs
  • I2C1 (GPIO2/3)
  • RPi's 3.3V I2C usually works with 5V PCF8574 but is out of spec — consider level shifter

ESP32 Notes:

  • I2C backpack strongly recommended
  • ESP32 is 3.3V only — needs level shifter for direct 5V LCD parallel interface

Gotchas:

  • PCF8574 address 0x27 collides with MCP23017 (0x20-0x27)
  • Contrast potentiometer must be adjusted or display appears blank — #1 troubleshooting issue
  • Backlight can be controlled via PCF8574 register bit

e-Paper / e-Ink Display (Waveshare-style)

  • Interface：SPI
  • Required Pins：MOSI, SCLK, CS, DC, RST, BUSY (output from display)
  • I2C Address：N/A
  • Voltage：3.3V logic and power
  • Pull-ups：N/A

RPi Notes:

  • SPI0 (GPIO10 MOSI, GPIO11 SCLK, GPIO8 CE0)
  • DC, RST, BUSY on any available GPIOs
  • Waveshare HAT uses: RST=GPIO17, DC=GPIO25, CS=GPIO8, BUSY=GPIO24

ESP32 Notes:

  • Any SPI pins via GPIO matrix
  • BUSY must be on input-capable GPIO
  • Input-only pins (GPIO34-39) are fine for BUSY

Gotchas:

  • Refresh time is slow (1-15 seconds for full refresh)
  • Partial refresh is faster but causes ghosting over time
  • Do NOT refresh continuously — damages the panel
  • Different Waveshare models (1.54", 2.13", 2.7", 4.2", 7.5") use different drivers — NOT interchangeable in software

Category 5: Communication

nRF24L01 (2.4GHz Radio Transceiver)

  • Interface：SPI, GPIO
  • Required Pins：MOSI, MISO, SCLK, CSN (chip select), CE (chip enable). Optional: IRQ
  • I2C Address：N/A
  • Voltage：3.3V ONLY for VCC. SPI data pins are 5V tolerant
  • Pull-ups：N/A

RPi Notes:

  • SPI0 (GPIO10 MOSI, GPIO9 MISO, GPIO11 SCLK, GPIO8 CE0 for CSN)
  • CE on any GPIO (commonly GPIO17 or GPIO22)
  • IRQ on any GPIO
  • Add 10µF + 100nF capacitor across VCC/GND close to module — extremely sensitive to power supply noise

ESP32 Notes:

  • VSPI or any SPI pins via GPIO matrix
  • CE on any output GPIO
  • Avoid strapping pins for CE
  • Power supply decoupling equally important

Gotchas:

  • PA+LNA variant draws up to 115mA — cannot be powered from typical breadboard 3.3V regulator
  • Use dedicated 3.3V supply
  • Range: basic module ~100m line of sight, PA+LNA ~1km+
  • CSN is NOT the same as CE — CSN is SPI chip select, CE is nRF24-specific enable pin

HC-05 / HC-06 (Bluetooth Classic Serial)

  • Interface：UART
  • Required Pins：TX, RX. Optional: STATE/STATUS, EN/KEY (AT mode on HC-05)
  • I2C Address：N/A
  • Voltage：3.3V logic (module VCC 3.6–6V). Use voltage divider for 5V TX
  • Pull-ups：N/A

RPi Notes:

  • GPIO14 (TX) / GPIO15 (RX)
  • On Pi 3/4/Zero2W, use dtoverlay=disable-bt or dtoverlay=miniuart-bt
  • Pi 5 has no conflict
  • RPi TX → HC-05/06 RX, RPi RX → HC-05/06 TX (crossover)

ESP32 Notes:

  • UART1 or UART2 on any GPIO pair
  • Less commonly used since ESP32 has built-in Bluetooth
  • Useful for bridging to Bluetooth Classic devices

Gotchas:

  • HC-05 is master/slave capable, HC-06 is slave only
  • Default baud rate: 9600 (HC-06), 38400 (HC-05 AT mode)
  • HC-05 enters AT mode by holding EN/KEY HIGH during power-up
  • Bluetooth Classic (not BLE) — not compatible with iOS without MFi

SX1276 / RFM95W (LoRa Radio)

  • Interface：SPI, GPIO
  • Required Pins：MOSI, MISO, SCLK, NSS/CS, RST, DIO0 (interrupt). Optional: DIO1-DIO5
  • I2C Address：N/A
  • Voltage：3.3V
  • Pull-ups：N/A

RPi Notes:

  • SPI0 (GPIO10 MOSI, GPIO9 MISO, GPIO11 SCLK, GPIO8 CE0)
  • RST on any GPIO
  • DIO0 on any GPIO (commonly GPIO25)
  • NSS can use GPIO8 (CE0) or any GPIO as software CS

ESP32 Notes:

  • Any SPI pins via GPIO matrix
  • DIO0 to any input-capable GPIO
  • Input-only pins (GPIO34-39) are fine for DIO0

Gotchas:

  • LoRa operates in ISM bands (433/868/915 MHz) — use correct frequency for your country
  • Antenna MUST be connected before transmitting or module can be damaged
  • RFM95W is the HopeRF clone of SX1276 — pin-compatible and functionally identical

MCP2515 (CAN Bus Controller)

  • Interface：SPI, GPIO
  • Required Pins：MOSI, MISO, SCLK, CS, INT. Needs external CAN transceiver (TJA1050/MCP2551)
  • I2C Address：N/A
  • Voltage：2.7–5.5V. Most modules include transceiver and run at 5V
  • Pull-ups：N/A

RPi Notes:

  • SPI0 with dtoverlay=mcp2515-can0,oscillator=8000000,interrupt=25
  • Adjust oscillator to match board crystal (8MHz or 16MHz)
  • INT on GPIO (commonly GPIO25)
  • Adds can0 network interface
  • Second bus: dtoverlay=mcp2515-can1,oscillator=8000000,interrupt=24 on SPI0 CE1

ESP32 Notes:

  • Any SPI pins
  • INT to any input-capable GPIO
  • ESP32 has built-in CAN (TWAI) — MCP2515 useful for second CAN bus
  • Still needs external transceiver

Gotchas:

  • Oscillator frequency in overlay MUST match physical crystal — check markings (8MHz or 16MHz common)
  • Wrong oscillator value = CAN bus won't work
  • CAN bus requires 120Ω termination resistors at both ends
  • Some modules include termination resistor — check before adding another

ENC28J60 (SPI Ethernet Controller)

  • Interface：SPI, GPIO
  • Required Pins：MOSI, MISO, SCLK, CS, INT. Optional: RST (can tie to VCC)
  • I2C Address：N/A
  • Voltage：3.3V
  • Pull-ups：N/A

RPi Notes:

  • SPI0 with dtoverlay=enc28j60,int_pin=25,speed=12000000
  • INT on GPIO (commonly GPIO25)
  • Adds eth1 network interface
  • Max speed is 10 Mbps (10Base-T only)

ESP32 Notes:

  • Any SPI pins via GPIO matrix
  • Less commonly used since many ESP32 boards have built-in WiFi
  • Useful for wired-only industrial applications

Gotchas:

  • 10 Mbps only — no 100 Mbps or gigabit
  • Uses significant CPU time due to SPI polling
  • Not suitable for high-bandwidth applications
  • MAC address usually set in software
  • Consider W5500 (100 Mbps, hardware TCP/IP stack) as modern alternative

Category 6: Motor Control

PCA9685 (16-Channel PWM/Servo Driver)

  • Interface：I2C
  • Required Pins：SDA, SCL. Optional: OE (output enable, active low)
  • I2C Address：0x40 (default). Configurable 0x40–0x7F via A0–A5 pins (62 addresses)
  • Voltage：VCC 3.3V–5V for logic. Separate V+ for servos (up to 6V)
  • Pull-ups：Provided on most breakouts

RPi Notes:

  • I2C1 (GPIO2/3)
  • No special overlay needed
  • 12-bit resolution, 24Hz–1526Hz adjustable frequency
  • OE pin to any GPIO if needed

ESP32 Notes:

  • Any GPIO pair for I2C
  • Useful for adding PWM channels or servo control

Gotchas:

  • ADDRESS COLLISION — default 0x40 collides with INA219
  • Must change address via A0-A5 pins if both on same bus
  • PCA9685 is a PWM driver, NOT a motor driver — generates PWM signals but cannot drive motors directly
  • Connect outputs to motor drivers (L298N, DRV8825) or directly to servos
  • All 16 channels share same PWM frequency

L298N (Dual H-Bridge Motor Driver)

  • Interface：GPIO (digital + PWM)
  • Required Pins：Per motor: IN1, IN2 (direction), ENA (PWM speed). 2 motors: 6 GPIOs total
  • I2C Address：N/A
  • Voltage：Motor: 5–35V. Logic: 5V (on-board regulator if motor >7V). 3.3V tolerant
  • Pull-ups：N/A

RPi Notes:

  • IN1-IN4 on any GPIO
  • ENA/ENB on PWM-capable GPIO (GPIO12, GPIO13, GPIO18, GPIO19)
  • Use dtoverlay=pwm or dtoverlay=pwm-2chan for smooth control
  • Software PWM may cause audible motor whine

ESP32 Notes:

  • IN1-IN4 on any output GPIO
  • ENA/ENB on any GPIO (all support LEDC PWM)
  • Avoid strapping pins

Gotchas:

  • L298N has ~2V voltage drop across H-bridge — motor sees ~2V less than supply
  • Not efficient for battery-powered projects
  • 5V regulator on board can supply ~500mA for logic
  • TB6612FNG is a more efficient alternative (MOSFET-based, ~0.5V drop)

DRV8825 / A4988 (Stepper Motor Driver)

  • Interface：GPIO (digital)
  • Required Pins：STEP, DIR, ENABLE (active low, optional). MS1-MS3 (microstepping)
  • I2C Address：N/A
  • Voltage：DRV8825: 8.2–45V motor, 3.3V logic. A4988: 8–35V motor, 3.3V/5V logic
  • Pull-ups：ENABLE has internal pull-down. STEP/DIR do not need pull-ups

RPi Notes:

  • STEP on any GPIO (consider hardware PWM on GPIO12/13/18/19 for constant speed)
  • DIR on any GPIO
  • ENABLE on any GPIO

ESP32 Notes:

  • STEP on any output GPIO
  • Use LEDC PWM or RMT peripheral for consistent step timing
  • Avoid strapping pins

Gotchas:

  • DRV8825: up to 1/32 microstepping. A4988: up to 1/16
  • Current limit must be set via potentiometer BEFORE connecting motor
  • NEVER disconnect motor while driver is powered — back-EMF can destroy driver
  • A4988 and DRV8825 have same pinout but different microstepping truth tables

Category 7: Other

MCP23017 (16-Channel GPIO Expander)

  • Interface：I2C
  • Required Pins：SDA, SCL. Optional: INTA, INTB (interrupts), RST (active-low reset)
  • I2C Address：0x20–0x27 (A0, A1, A2 = 8 configurable addresses)
  • Voltage：1.8–5.5V
  • Pull-ups：Provided on most breakouts. GPIO pins have optional internal pull-ups

RPi Notes:

  • I2C1 (GPIO2/3)
  • Connect INTA/INTB to RPi GPIOs for interrupt-driven input
  • Up to 8 expanders = 128 additional GPIOs

ESP32 Notes:

  • Any GPIO pair for I2C
  • Less commonly needed since ESP32 has many GPIOs
  • Useful for projects needing many inputs with interrupt support

Gotchas:

  • Address range 0x20–0x27 collides with PCF8574 (HD44780 I2C backpacks)
  • If using both, ensure non-overlapping addresses
  • Each output pin can source/sink 25mA (total per port: 125mA)
  • PCF8574 is the 8-channel version with same address range

WS2812B / NeoPixels (Addressable RGB LEDs)

  • Interface：Single GPIO (proprietary protocol — NOT Dallas 1-Wire)
  • Required Pins：DIN (1 GPIO). Chain DOUT→DIN between LEDs
  • I2C Address：N/A
  • Voltage：5V power. Data expects 5V logic (min 3.5V for logic high)
  • Pull-ups：N/A. Add 300–500Ω resistor on data line. Add 1000µF capacitor at power

RPi Notes:

  • USE GPIO18 (PWM0/PCM) or GPIO10 (SPI0 MOSI) or GPIO21 (PCM)
  • rpi_ws281x library requires specific GPIOs (DMA-based timing)
  • GPIO18 most common. GPIO10 requires dtparam=spi=on
  • Needs sudo or specific permissions for DMA access
  • RPi outputs 3.3V — use level shifter (3.3V→5V) for reliable operation

ESP32 Notes:

  • Any output GPIO via RMT peripheral
  • ESP32 outputs 3.3V — same level shifting recommendation
  • RMT peripheral handles timing precisely without CPU intervention

Gotchas:

  • LEVEL SHIFTER WARNING — 3.3V logic is below WS2812B spec (needs >3.5V)
  • Works unreliably at short distances, fails with longer data lines
  • Use 74AHCT125, 74HCT245, or SN74LV1T34 level shifter
  • Each LED draws up to 60mA at full white — 60 LEDs = 3.6A
  • Inject power every 30-50 LEDs for long strips
  • SK6812 is compatible alternative with RGBW support

Rotary Encoder (Incremental, with push button)

  • Interface：GPIO (digital inputs)
  • Required Pins：CLK/A, DT/B (encoder phases), SW (push button, active low)
  • I2C Address：N/A
  • Voltage：3.3V–5V (module dependent)
  • Pull-ups：Most modules have 10kΩ on board. Bare encoder needs pull-ups

RPi Notes:

  • Use any 3 GPIOs with interrupt support (all RPi GPIOs support edge-triggered interrupts)
  • Enable internal pull-ups via gpiod or RPi.GPIO if bare encoder

ESP32 Notes:

  • Any 3 input-capable GPIOs
  • Hardware interrupt on all GPIOs
  • Input-only pins (GPIO34-39) work fine
  • Avoid strapping pins

Gotchas:

  • Mechanical encoders generate switch bounce — need debouncing
  • Hardware: 100nF capacitor across each pin to GND
  • Software: 1-5ms delay
  • Optical encoders don't bounce
  • Reading must use interrupt or high-frequency polling — slow polling misses steps
  • KY-040 is the most common breakout module

Relay Modules (1/2/4/8 channel)

  • Interface：GPIO (digital output)
  • Required Pins：IN1 (one GPIO per channel). Multi-channel: IN1, IN2, IN3, IN4, etc.
  • I2C Address：N/A
  • Voltage：Module VCC typically 5V. Most blue relay modules are ACTIVE LOW
  • Pull-ups：N/A

RPi Notes:

  • Any GPIO
  • Check if module is active-low or active-high
  • Most cheap modules are active-low — relay activates when GPIO goes LOW
  • At boot, GPIOs are floating — may cause relay chatter
  • Use pull-up resistor to keep relay OFF during boot

ESP32 Notes:

  • Any output GPIO
  • Same active-low/high consideration
  • Avoid strapping pins (GPIO0, 2, 5, 12, 15) — boot states could trigger relays
  • Avoid GPIO34-39 (input only)

Gotchas:

  • Most modules have opto-isolated inputs
  • Remove VCC-JD jumper for true isolation
  • Relay coils cause voltage spikes — modules should have flyback diodes (most do)
  • Never switch mains voltage without proper safety knowledge
  • For DC loads, consider MOSFETs instead

MAX31855 / MAX6675 (Thermocouple Interface)

  • Interface：SPI (read-only — no MOSI needed)
  • Required Pins：MISO/SO, SCLK/SCK, CS. No MOSI needed
  • I2C Address：N/A
  • Voltage：MAX31855: 3.0–3.6V. MAX6675: 5V. Most breakouts accept both
  • Pull-ups：N/A

RPi Notes:

  • SPI0 (GPIO9 MISO, GPIO11 SCLK, GPIO8 CE0)
  • MOSI (GPIO10) unused but SPI0 still claims it

ESP32 Notes:

  • Any SPI pins via GPIO matrix
  • MOSI unused — can reassign to other functions

Gotchas:

  • MAX31855 supports K, J, N, S, R, T type thermocouples — different variants for each
  • MAX6675 supports K-type only and is older/less accurate
  • Thermocouple wires are polarity-sensitive — red is always negative
  • Cold-junction compensation is built in
  • Keep chip close to terminal block to minimize cold-junction error
  • MAX31855 has open/short fault detection

I2C Address Collision Map

  • 0x76：Devices=BME280, BMP280, MS5611, Resolution=Use alternate 0x77 for one device, or I2C multiplexer
  • 0x77：Devices=BME280 (alt), BMP280 (alt), Resolution=Only one per bus at this address
  • 0x40：Devices=INA219, PCA9685, HDC1080, Resolution=Change address via A0/A1 pins
  • 0x44：Devices=SHT31, INA219 (A1=VDD,A0=GND), Resolution=Change INA219 address via A0/A1
  • 0x45：Devices=SHT31 (alt), INA219 (alt), Resolution=Change INA219 address via A0/A1
  • 0x3C：Devices=SSD1306, SH1106, Resolution=Different drivers, unlikely to use both
  • 0x3D：Devices=SSD1306 (alt), Resolution=Rare collision
  • 0x68：Devices=MPU6050, DS3231 RTC, Resolution=Set MPU6050 to 0x69 (AD0→VDD)
  • 0x69：Devices=MPU6050 (alt), Resolution=Rare collision
  • 0x48–0x4B：Devices=ADS1115 (configurable), TMP102, Resolution=Configure ADS1115 to non-conflicting address
  • 0x20–0x27：Devices=MCP23017 (A0-A2), PCF8574, HD44780 backpack, Resolution=Configure A0-A2 to avoid overlap
  • 0x27：Devices=PCF8574 (HD44780 backpack), MCP23017 (A0-A2 all high), Resolution=Change MCP23017 address
  • 0x42：Devices=NEO-GPS (I2C mode), Resolution=Uncommon, rarely conflicts

When address conflicts cannot be resolved via address pins, use a TCA9548A I2C multiplexer. Each TCA9548A has 8 channels and its own configurable address (0x70-0x77), supporting up to 64 separate I2C buses from a single host bus.

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