Reading sensor data over I2C in Raspberry Pi - Step-by-Step Execution

Concept Flow - Reading sensor data over I2C

Start

↓

Initialize I2C bus

↓

Set sensor address

↓

Send read command

↓

Read data bytes

↓

Process data

↓

Use or display data

↓

End or repeat

This flow shows how a Raspberry Pi talks to a sensor using I2C: start, set up bus, send command, read data, then use it.

Execution Sample

Raspberry Pi

import smbus
bus = smbus.SMBus(1)
sensor_addr = 0x48
data = bus.read_byte_data(sensor_addr, 0x00)
print(f"Sensor data: {data}")

This code reads one byte from a sensor at address 0x48 and prints it.

Execution Table

Step	Action	I2C Bus State	Sensor Address	Data Read	Output
1	Import smbus module	Not initialized	-	-	-
2	Initialize I2C bus 1	Bus 1 ready	-	-	-
3	Set sensor address to 0x48	Bus 1 ready	0x48	-	-
4	Send read command to register 0x00	Bus 1 ready	0x48	-	-
5	Read one byte from sensor	Bus 1 ready	0x48	72	-
6	Print sensor data	Bus 1 ready	0x48	72	Sensor data: 72

💡 Data read and printed; program ends or can repeat to read again.

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 5	Final
bus	None	SMBus(1) object	SMBus(1) object	SMBus(1) object	SMBus(1) object
sensor_addr	None	None	0x48	0x48	0x48
data	None	None	None	72	72

Key Moments - 3 Insights

Why do we initialize the bus with smbus.SMBus(1)?

The number 1 selects the I2C bus on Raspberry Pi (usually bus 1). This is shown in execution_table step 2 where the bus becomes ready.

What does the sensor address 0x48 mean?

It is the unique I2C address of the sensor device. In step 3, we set this address so the bus knows where to send commands.

Why do we read from register 0x00?

Register 0x00 is often the data register in sensors. Step 4 sends the read command to this register to get the sensor value.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'data' after step 5?

A 0x48

B 72

C None

D 1

💡 Hint

Check the 'Data Read' column at step 5 in the execution_table.

At which step is the I2C bus initialized?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the 'Action' column for bus initialization in the execution_table.

If the sensor address changed to 0x49, which execution_table step would change?

A Step 3 only

B Step 5 only

C Steps 3 and 5

D No steps change

💡 Hint

Sensor address is set at step 3 and used at step 5 in the execution_table.

Concept Snapshot

Reading sensor data over I2C on Raspberry Pi:
- Import smbus and create bus with smbus.SMBus(1)
- Set sensor I2C address (e.g., 0x48)
- Use bus.read_byte_data(address, register) to read data
- Process or print the data
- Repeat as needed for continuous reading

Full Transcript

This example shows how a Raspberry Pi reads data from a sensor using the I2C protocol. First, the smbus module is imported and the I2C bus 1 is initialized. Then, the sensor's I2C address is set to 0x48. A read command is sent to register 0x00 of the sensor. One byte of data is read from the sensor and stored in the variable 'data'. Finally, the data is printed to the screen. The execution table traces each step, showing the bus state, sensor address, data read, and output. Variables change as the program runs, with 'data' holding the sensor value after reading. Key moments clarify why bus 1 is used, what the sensor address means, and why register 0x00 is read. The visual quiz tests understanding of these steps. This process can be repeated to continuously read sensor data.