i2cdetect for device scanning in Raspberry Pi - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the i2cdetect command on a Raspberry Pi?

The i2cdetect command scans the I2C bus on a Raspberry Pi to find connected I2C devices by showing their addresses.

beginner

How do you specify which I2C bus to scan using i2cdetect?

You add the bus number as an argument, for example, i2cdetect -y 1 scans bus number 1.

intermediate

What does the -y option do in the i2cdetect command?

The -y option disables interactive confirmation, so the scan runs without asking for permission.

beginner

What does it mean if i2cdetect shows a number at a certain address?

It means an I2C device is detected at that address on the bus.

intermediate

Why might i2cdetect show UU at some addresses?

UU means the address is in use by a driver and is busy, so i2cdetect cannot scan it.

What command scans I2C bus 1 for devices without asking for confirmation?

A i2cdetect -y 1

B i2cdetect 1

C i2cdetect -n 1

D i2cdetect -q 1

The -y option disables confirmation, so i2cdetect -y 1 scans bus 1 directly.

If i2cdetect shows a number at address 0x3C, what does it mean?

A No device found at 0x3C

B Address 0x3C is reserved

C Bus error at 0x3C

D Device detected at 0x3C

A number at an address means a device is detected there.

What does the UU symbol mean in i2cdetect output?

A No device detected

B Unknown device

C Device busy, address in use by driver

D Scan error

UU means the address is busy because a driver is using it.

Which bus number is commonly used for I2C on Raspberry Pi models after revision 2?

A 1

B 0

C 2

D 3

Bus 1 is the default I2C bus on Raspberry Pi models after revision 2.

Why should you run i2cdetect with sudo?

A To scan faster

B To access hardware bus permissions

C To save output to a file

D To update I2C drivers

Root permissions are needed to access the I2C hardware bus.

Explain how to use i2cdetect to find devices connected to your Raspberry Pi's I2C bus.

Think about the command format and what the output numbers mean.

Describe what the symbols and numbers in the i2cdetect output represent.

Focus on how to read the scan results.

Practice

1. What is the main purpose of the i2cdetect command on a Raspberry Pi?

easy

A. To update the Raspberry Pi operating system

B. To scan the I2C bus and list connected devices

C. To check the Wi-Fi signal strength

D. To format the SD card

Solution

1. Step 1: Understand the function of i2cdetect

   The i2cdetect command scans the I2C bus to find devices connected to it.

2. Step 2: Compare with other options

   Options A, C, and D relate to system update, Wi-Fi, and storage, which are unrelated to I2C scanning.

3. Final Answer:

   To scan the I2C bus and list connected devices -> Option B

4. Quick Check:

   i2cdetect scans I2C devices = B [OK]

Hint: Remember: i2cdetect scans I2C devices only [OK]

Common Mistakes:

• Confusing i2cdetect with system update commands
• Thinking it checks Wi-Fi or storage
• Assuming it formats devices

2. Which of the following is the correct syntax to scan I2C devices on bus 1 using i2cdetect?

easy

A. i2cdetect --bus 1

B. i2cdetect -scan 1

C. sudo i2cdetect -y 1

D. sudo i2cdetect 1 -y

Solution

1. Step 1: Recall the correct command format

   The correct syntax is sudo i2cdetect -y 1 where -y disables interactive confirmation and 1 is the bus number.

2. Step 2: Check other options for errors

   Options A, B, and C use incorrect flags or order, making them invalid.

3. Final Answer:

   sudo i2cdetect -y 1 -> Option C

4. Quick Check:

   Correct syntax = sudo i2cdetect -y 1 [OK]

Hint: Use sudo i2cdetect -y followed by bus number [OK]

Common Mistakes:

• Switching flag order or using wrong flags
• Omitting sudo causing permission errors
• Using non-existent flags like --bus

3. After running sudo i2cdetect -y 1, you see the following output snippet:

     00: -- -- -- -- -- -- -- -- 
     10: -- -- -- -- -- -- -- -- 
     20: -- -- -- -- -- -- -- -- 
     30: -- -- -- -- -- -- -- -- 
     40: -- -- -- -- -- -- -- -- 
     50: -- -- -- -- -- -- -- -- 
     60: -- -- -- -- -- -- -- -- 
     70: 70 -- -- -- -- -- -- -- 

What does the address 0x70 in the output indicate?

medium

A. The command failed to run

B. No device is connected at address 0x70

C. The I2C bus is disabled

D. An I2C device is detected at address 0x70

Solution

1. Step 1: Interpret i2cdetect output

   Addresses with numbers (like 70) show detected devices; dashes mean no device.

2. Step 2: Analyze the given output

   Only address 0x70 shows a number, so a device is present there.

3. Final Answer:

   An I2C device is detected at address 0x70 -> Option D

4. Quick Check:

   Number in table = device present [OK]

Hint: Numbers show devices; dashes mean no device [OK]

Common Mistakes:

• Thinking dashes mean devices
• Assuming output means error
• Confusing address with bus number

4. You run i2cdetect -y 1 without sudo and get a permission error. How do you fix this?

medium

A. Run the command with sudo as sudo i2cdetect -y 1

B. Add --force flag to bypass permissions

C. Change the bus number to 0

D. Restart the Raspberry Pi

Solution

1. Step 1: Understand permission requirements

   Accessing I2C bus requires root privileges, so sudo is needed.

2. Step 2: Apply correct fix

   Running sudo i2cdetect -y 1 grants permission and avoids error.

3. Final Answer:

   Run the command with sudo as sudo i2cdetect -y 1 -> Option A

4. Quick Check:

   Use sudo for I2C commands = C [OK]

Hint: Always use sudo with i2cdetect to avoid permission errors [OK]

Common Mistakes:

• Trying to bypass permissions with wrong flags
• Changing bus number unnecessarily
• Restarting without fixing permissions

5. You want to scan I2C devices on bus 0 and bus 1, but sudo i2cdetect -y 0 shows no devices, while bus 1 shows several. What is the best explanation?

hard

A. Bus 0 is usually reserved or unused on most Raspberry Pi models

B. Bus 0 devices are hidden and require a special flag

C. Bus 1 is disabled by default and must be enabled manually

D. The i2cdetect command only works on bus 1

Solution

1. Step 1: Know Raspberry Pi I2C bus defaults

   Most Raspberry Pi models use bus 1 for I2C; bus 0 is often reserved or inactive.

2. Step 2: Analyze scan results

   Devices appear on bus 1 but not on bus 0, confirming bus 0 is unused.

3. Final Answer:

   Bus 0 is usually reserved or unused on most Raspberry Pi models -> Option A

4. Quick Check:

   Bus 0 unused, bus 1 active = A [OK]

Hint: Bus 1 is main I2C bus; bus 0 often unused [OK]

Common Mistakes:

• Thinking bus 0 devices are hidden
• Assuming i2cdetect only works on bus 1
• Believing bus 1 is disabled by default