I2C Master Slave I/O

Introduction

This tutorial guides you through setting up I2C communication between a master and a slave device using a NEXTuino. The master reads analog and digital inputs and sends data to the slave; the slave responds with data that controls outputs on the master.

Prerequisites

  • Installed Arduino IDE
  • NEXTuino board (MINI, MAXI, or MEGA)
  • Basic understanding of I2C communication and pin setup

The I2C connection uses the SDA and SCL pins on the X1 connector (same pins for MINI, MAXI and MEGA).

Example Code

Step-by-Step Guide

Step 1: Setup the Arduino Environment

  1. Connect your NEXTuino board to your computer
  2. Open the Arduino IDE and select the correct board and port
  3. Include the Wire and NEXTuino libraries

Step 2: Initialize I2C Communication

In setup():

  • Initialize I2C as master: Wire.begin()
  • Initialize serial for debugging: Serial.begin(9600)

Step 3: Configure Digital and Analog Pins

  • Digital Inputs: NEXTuino_D0 to NEXTuino_D4 as inputs
  • Relay Outputs: NEXTuino_R0 to NEXTuino_R4 as outputs
  • Analog Inputs: NEXTuino_A0 and NEXTuino_A1
  • PWM Outputs: same pins configured as outputs

Step 4: Sending Data to the Slave

In loop():

  1. Begin transmission: Wire.beginTransmission(slaveAddress)
  2. Read analog inputs, split each 10-bit value into two bytes, send with Wire.write()
  3. Read digital input states, pack into one byte using bitwise ops, send with Wire.write()

Step 5: Receiving Data from the Slave

  1. End transmission: Wire.endTransmission()
  2. Request data: Wire.requestFrom(slaveAddress, 5)
  3. Read digital output states byte, update output pins
  4. Combine two bytes into integer for analog data, set PWM outputs

Step 6: Slave Setup

The slave initializes with a specific I2C address: Wire.begin(8) (must match master’s slaveAddress).

Pin configuration mirrors the master.

Step 7: Slave Receive Handler (receiveEvent)

When master sends data:

  1. Reconstruct analog values from two bytes each
  2. Write values to PWM output pins
  3. Read digital output states byte and set output pins with digitalWrite()

Step 8: Slave Request Handler (requestEvent)

When master requests data:

  1. Read analog inputs, split into two bytes
  2. Read digital inputs, pack into one byte
  3. Send all bytes back with Wire.write()

Troubleshooting

  • Ensure slave I2C address matches slaveAddress in master code
  • Check SDA and SCL wiring between master and slave
  • Verify correct board and port in Arduino IDE

Conclusion

You have established I2C communication between a NEXTuino master and slave. The master reads analog and digital inputs and controls outputs based on data received from the slave, enabling synchronized bidirectional control between two devices.

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