Air724UG Software Guide: I2C Example

For the latest documentation content, see:

1. Introduction

The I2C bus (Inter-Integrated Circuit) is a simple, bidirectional, two-wire synchronous serial bus developed by Philips. It requires only two wires to transmit information between devices connected to the bus.

The Air724UG module provides 2 I2C interfaces, supporting speeds of FAST (400KHz), SLOW (100KHz), and 3500KHz. Peripheral addresses support 0x00-0x7f.

1.1 Features

1.2 Module I2C Function List

Note: Please prioritize using I2C2; I2C1 is reserved for camera use.

2. Overview of Demonstration Functionality

This tutorial teaches you how to use the Air724 development board to demonstrate I2C functionality, read temperature and humidity from the AHT10 digital temperature and humidity sensor, and observe experimental results through logs.

3. Preparing the Hardware Environment

3.1 Development Board Preparation

Use the EVB_Air724 development board, as shown in the figure below:

For detailed instructions on using this development board, refer to: https://docs.openluat.com/air724ug/product/

In the Air724UG product manual, see the “EVB_Air724UG_AXX Development Board User Guide”; the latest version of the user guide at the time of writing this article is: “EVB_Air724UG_A14 Development Board User Guide”; if you encounter any issues during the use of the development board, you can directly refer to this user guide.

API: https://doc.openluat.com/wiki/21?wiki_page_id=2068

3.2 AHT10 Module

AHT10 digital temperature and humidity sensor module

3.3 Data Communication Line

One USB data cable (micro USB).

3.4 PC Computer

Windows 7 and above versions of Windows.

3.5 SIM Card

A SIM card that can access the internet in mainland China. Generally, using IoT cards or mobile cards from China Mobile, China Telecom, or China Unicom is acceptable.

3.6 Assembling the Hardware Environment

Insert the USB data cable into the USB port, connect the other end to the computer, set all DIP switches to ON, select UART1 for the serial switch, set the USB power switch corresponding to 4V to ON, and lock the SIM card into the SIM card slot, as shown in the figure below.

3.7 Connecting the Mainboard and Sensor

Ensure that SDA, SCL, GND, and VIN are connected between the mainboard and the sensor, as shown in the figure below.

4. Preparing the Software Environment

4.1 Download Debugging Tools

Refer to the instructions:

Luatools download and detailed usage: https://docs.openluat.com/Luatools/

4.2 Source Code and Firmware

1. Download the low-level core

Download the low-level firmware and unzip it

Link: https://docs.openluat.com/air724ug/luatos/firmware/

As shown in the figure below, the red box indicates what we need to use.

2. The demo used in this tutorial:

https://gitee.com/openLuat/LuatOS-Air724UG/tree/master/script_LuaTask/demo/peripheral/%E6%B8%A9%E6%B9%BF%E5%BA%A6%E4%BC%A0%E6%84%9F%E5%99%A8/AHT10

4.3 Downloading Firmware and Scripts to the Development Board

Open Luatools, power on the development board, and if the boot is successful, Luatools will print the following information.

Click on project management test options.

Enter the management interface, as shown in the figure below.

5. Introduction to Code Examples

5.1 API Description

5.1.1 i2c.setup( id, speed [,slaveaddr] [,isbaud] [,reg16bit])

Open the i2c interface

Parameters

Return Value

Example

5.1.2 i2c.write( id, reg, data )

Transmit data to the specified register address reg

Parameters

Return Value

Example

5.1.3 i2c.read( id, reg, num )

Read the data content of the specified register address reg

Parameters

Return Value

Example

5.1.4 i2c.send( id,slave, data )

Write data to the slave device

Parameters

Return Value

Example

5.1.5 i2c.recv( id, slave,size )

Read data from the slave device

Parameters

Return Value

Example

5.1.6 i2c.close( id )

Close the I2C interface

Parameters

Return Value

None

5.2 AHT10.lua Code

Open the AHT10 sensor, read the temperature and humidity registers, interpret the temperature and humidity data, and print logs.

5.3 main.lua Code

This code is the main program script; after the system starts, it will first configure the 4G network, wait for the network connection to succeed, and then load the test module.

6. Boot Debugging

6.1 Powering on the Development Board

After connecting the hardware and downloading the firmware, start the Luatools software; the system running information will be displayed on the interface. The red box shows the normal printed information after the development board is connected to the PC, as shown in the figure below.

6.2 Function Debugging

The system continuously prints temperature and humidity data.

7. Common Questions

7.1 Does I2C need to be set up each time before reading or writing data?

No, it is not necessary.

The normal business logic is:

i2c.setup

… You can read and write data multiple times here

i2c.close

After setup, as long as it is not closed, you can repeatedly read and write data.

Once close is executed, you must set up again before reading or writing data next time.

7.2 Can the module act as a slave device during I2C communication?

Note: The module I2C can only act as a master device, and external pull-up is required; when configuring for FAST speed, the pull-up resistor value should not exceed 4.7K.

7.3 If the levels of the master and slave devices are different during I2C communication, do I need to perform level conversion?

If the reference levels of the master and slave devices are inconsistent, please pay attention to perform level conversion. As shown in the figure:

7.4 If the I2C device’s 7-bit address is 0x38, do I need to manually convert it to an 8-bit address?

Here, the i2c_addr address is a 7-bit address;

If the I2C peripheral manual provides an 8-bit address, you need to right shift the 8-bit address by 1 bit and assign it to the i2c_addr variable;

If the I2C peripheral manual provides a 7-bit address, you can directly assign the 7-bit address to the i2c_addr variable.