For fast push-pull signals such as SPI displays, UARTs and parallel buses, the TXS0108E (about 4.4 stars from 130 ratings) shifts eight channels at once with automatic direction sensing and much faster edges than the MOSFET boards. The catch: it can misbehave on lines with strong pull-ups or heavy loads, so it’s a poor choice for I2C and for driving LEDs or long cables. Pull its OE (enable) pin high to activate the outputs.

The original ESP32 has two 8-bit DAC channels, and newer chips such as the ESP32-S3 and C3 have no DAC at all. The MCP4725 (about 4.0 stars from 64 ratings) adds a 12-bit analog output over I2C, with an EEPROM that remembers the output level through power cycles. Use it to set a motor speed controller, generate a reference voltage, or drive a 0–10 V industrial input through an op-amp. A PWM output with an RC filter is the cheaper alternative when precision doesn’t matter.

Most ESP32 chips have a CAN controller built in (Espressif calls it TWAI), so to join a CAN bus you only need a transceiver that converts its TX and RX pins to the differential bus. Waveshare’s SN65HVD230 board (about 4.6 stars from 171 ratings) runs at 3.3 V, so it connects directly to the ESP32, and adds ESD protection. Use it for vehicle diagnostics (read-only, carefully), solar inverters and battery systems, robotics and industrial equipment. The bus needs 120 Ω termination at each end; check whether your segment already has it before enabling the board’s resistor.

RS485 is how industrial devices talk: energy meters, solar inverters, VFDs, HVAC controllers and sensors using Modbus RTU. These modules (about 4.5 stars from 71 ratings) work at 3.3 V and have automatic flow control, so you only connect TX and RX; there’s no direction pin to toggle in software, which removes a common source of Modbus bugs. ESPHome’s Modbus components and Arduino Modbus libraries work with them directly. Twisted-pair cable and termination at both ends of long runs keep the bus reliable. 19 were in stock when we checked.

When a Modbus device won’t answer, you need to see the bus from your PC. Waveshare’s USB to RS485 converter (about 4.6 stars from 145 ratings) uses a CH343G chip in a protected industrial housing. Pair it with free Modbus master software to talk to a meter directly and confirm its address, baud rate and register map before you write ESP32 code, or use it to sniff traffic between your ESP32 and the device. It saves hours of guesswork. 9 were in stock when we checked.

Running out of GPIOs is the most common ESP32 frustration, especially on boards where many pins are tied to flash, PSRAM or strapping. The MCP23017 (Waveshare’s board has about 4.3 stars from 99 ratings) adds 16 general-purpose pins over two I2C wires, with interrupt outputs so the ESP32 is notified instantly when a button changes, and internal pull-ups. Eight address options mean up to 128 extra pins on one bus. ESPHome supports it natively. It’s ideal for control panels, keypads, relay banks and status LEDs.

The PCF8574 (about 4.2 stars from 62 ratings) is the simpler, cheaper expander, with 8 pins over I2C, and the same chip used on most I2C LCD backpacks. Its “quasi-bidirectional” pins have only a weak pull-up when high, so they’re great for reading buttons or sinking current to light an LED, but they can’t source much current. These boards stack, so you can chain several with different addresses. 12 were in stock when we checked.

Many sensors have a fixed I2C address, so you can’t put two of the same model on one bus. The TCA9548A multiplexer creates eight separate downstream buses that the ESP32 switches between, so you can read eight identical sensors, such as SHT31s in eight rooms of a greenhouse. SparkFun’s version (about 4.6 stars from 24 ratings) adds Qwiic connectors for solder-free wiring. Isolating sections of a long bus also helps with capacitance. Only 4 were in stock when we checked.

The CD74HC4067 routes 16 analog or digital signals to a single ESP32 pin, selected by four GPIOs. It’s the classic way to read many potentiometers (MIDI controllers), soil sensors or a keyboard matrix with one ADC1 input. This 10-pack (about 4.5 stars from 36 ratings) is cheap enough to use freely. Power it from 3.3 V so the signals stay within the ESP32’s range, and allow a few microseconds after switching channels before reading. 13 were in stock when we checked.

An optocoupler passes a signal through light, so there’s no electrical connection between two circuits. That’s how you safely read 12 V or 24 V industrial signals, doorbell circuits, alarm panel outputs or pulse outputs from utility meters with a 3.3 V ESP32. These PC817 chips (about 4.6 stars from 262 ratings for the 20-pack) need an input resistor sized for the source voltage and a pull-up on the ESP32 side. Mount them on perfboard with a terminal block for a robust isolated input board. They’re too slow for fast signals, but perfect for anything under a few kilohertz.

A 5 V sensor or LCD

BSS138 converter for I2C; TXS0108E for SPI.

A Modbus meter or inverter

RS485 module + USB-RS485 for debugging.

A CAN bus

SN65HVD230 + the ESP32’s built-in TWAI.

A control panel

MCP23017 for buttons and LEDs; CD74HC4067 for knobs.

Accurate measurements

ADS1115 in; MCP4725 out.

12/24 V inputs

PC817 optocouplers on perfboard.

Are ESP32 pins 5 V tolerant?

No. ESP32 GPIOs are rated for 3.3 V, and applying 5 V can damage the chip or shorten its life. Use a level shifter or a voltage divider for any 5 V signal going into the ESP32. Many 5 V devices do accept 3.3 V signals as a valid high, so outputs from the ESP32 often work without shifting, but check the device’s datasheet.

Do I need an MCP2515 for CAN on the ESP32?

Usually not. Most ESP32 chips include a TWAI controller compatible with CAN 2.0, so a 3.3 V transceiver like the SN65HVD230 is enough. An MCP2515 is only useful if you need an extra CAN interface beyond the built-in one.

How many I2C devices can I connect?

As many as have unique addresses, within the bus’s capacitance limit (keep wires short). The classic ESP32 and ESP32-S3 also have two I2C controllers (the C3 has one), so you can run two separate buses, and a TCA9548A multiplexer adds eight more.

Should I isolate RS485 and CAN connections?

For short runs between devices on the same power supply, non-isolated modules are fine. For long cable runs, separate buildings, or equipment on different power systems, use isolated transceivers to avoid ground loops and damage from surges. Industrial ESP32 boards often include isolation; see our relay and industrial board guide.