i2cdetect for device scanning in Raspberry Pi - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this i2cdetect command?

You run the command i2cdetect -y 1 on your Raspberry Pi. The output shows a grid with addresses and some numbers. What does the number 3c in the grid represent?

Raspberry Pi

i2cdetect -y 1
     0 1 2 3 4 5 6 7 8 9 a b c d e f
00:          -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- 3c -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --

A It means the device at address 0x3c is not responding.

B It indicates a syntax error in the command.

C It shows an I2C device is detected at address 0x3c on bus 1.

D It shows the Raspberry Pi I2C bus is disabled.

💡 Hint

Look at the grid and what the numbers mean in the i2cdetect output.

The number 3c in the grid means an I2C device was found at address 0x3c on bus 1. The -- means no device detected at those addresses.

🧠 Conceptual

intermediate

Why do you use the '-y' option with i2cdetect?

When running i2cdetect, what is the purpose of the -y option?

A It disables interactive mode and runs the scan without asking for confirmation.

B It enables verbose output showing extra debug information.

C It specifies the I2C bus number to scan.

D It resets the I2C bus before scanning.

💡 Hint

Think about what happens if you run i2cdetect without -y.

The -y option disables the interactive confirmation prompt so the scan runs immediately without asking the user.

❓ Predict Output

advanced

What error does this i2cdetect command produce?

You run the command i2cdetect -y 3 on a Raspberry Pi that only has bus 0 and 1. What error message will you see?

Raspberry Pi

i2cdetect -y 3

A Error: Bus 3 is busy, try again later

B No error, it scans bus 3 successfully

C Error: Permission denied to access I2C bus 3

D Error: Could not open file `/dev/i2c-3`: No such file or directory

💡 Hint

Check which I2C buses exist on a Raspberry Pi by default.

Bus 3 does not exist by default, so the device file `/dev/i2c-3` is missing, causing a 'No such file or directory' error.

🚀 Application

advanced

How to scan all I2C buses on a Raspberry Pi?

You want to scan all available I2C buses on your Raspberry Pi to find connected devices. Which script correctly scans buses 0 and 1?

A i2cdetect -y 0 | i2cdetect -y 1

B for bus in 0 1; do i2cdetect -y $bus; done

C i2cdetect -y 0 && i2cdetect -y 1

D i2cdetect -y 0 1

💡 Hint

Think about how to run a command multiple times for different bus numbers.

Option B uses a loop to run i2cdetect on each bus separately. Option B is invalid syntax. Option B runs two commands but not in a loop. Option B pipes output incorrectly.

🔧 Debug

expert

Why does i2cdetect show all addresses as '--' despite devices connected?

You connect an I2C device to your Raspberry Pi and run i2cdetect -y 1. The output shows -- for all addresses, but you are sure the device is connected and powered. What is the most likely cause?

A The I2C interface is disabled in Raspberry Pi configuration.

B The device address is outside the scanned range.

C The device is connected to a different I2C bus number.

D The device is not powered properly.

💡 Hint

Check Raspberry Pi settings for I2C interface status.

If the I2C interface is disabled in the Raspberry Pi settings, i2cdetect will not find any devices and show all --.