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I am trying to set up multiple I2C interfaces on my pi.

I have added the following lines to my /boot/config.txt and rebooted:

dtoverlay=i2c-gpio,bus=4,i2c_gpio_delay_us=1,i2c_gpio_sda=29,i2c_gpio_scl=31

dtoverlay=i2c-gpio,bus=3,i2c_gpio_delay_us=1,i2c_gpio_sda=35,i2c_gpio_scl=37

I have pull up resistors, and one i2c device wired to each of those pairs of pins with corresponding SDA/SCL. However, running i2cdetect -l shows this:

i2c-3 i2c i2c@3 I2CAdapter

Have I done something wrong? I have i2c-dev enabled via modprobe, and I have also enabled the I2C interface via raspi-config. Is there something else I need to do?

EDIT: Note, the i2c-3 bus shows up empty.

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5
  • Are you using a compute module? Standard Pis only have GPIO 0-27.
    – joan
    Commented Sep 30, 2019 at 15:14
  • @joan I don't think so, but pinout.xyz has the GPIO pins going 1-40
    – Tmello225
    Commented Sep 30, 2019 at 15:32
  • @joan According to the Rpi website, the 3B+ comes standard with a 40 pin gpio header. Is there something special I have to do to use dtoverlay with those extra pins?
    – Tmello225
    Commented Sep 30, 2019 at 15:38
  • 1
    Looks like you're using the physical pin numbers. You need to use the BCM numbers as they are listed on the pinout website
    – Dirk
    Commented Sep 30, 2019 at 16:16
  • @Dirk THAT WORKED! If you would like to add it as an answer I'll mark it as correct!
    – Tmello225
    Commented Sep 30, 2019 at 16:25

2 Answers 2

Reset to default
4

Looks like you're using the physical pin numbers.

All RPF documentation, settings and software (such as dtoverlay, gpiozero, etc) work with the BCM numbers. You can find these at pinout and elsewhere.

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-1

Question

How to set up multiple I2C buses on Rpi3B+ and Rpi4B?

Answer

I often read forum discussions on setting I2C buses. I tried all for my Rpi3B+'s but all failed, perhaps my drivers or Rpi stretch was to updated. The guys saying it is OK never specified their os version or driver used.

I tried again for Rpi4B and found that I could use at least 2 buses very stable, 3 buses more or less stable, depending on length of connecting wires.

i2cdetect shows 5 busses, but only first 4 working, but not stable.

To do - I read that a new buster sep26 version is more stable (2019 june versions were bad.)

This is a summary of the config proved working. More details in Appendix A below

dtoverlay=i2c1,pins_2_3 (board pins 3, 5)

dtoverlay=i2c3,pins_4_5 (board pins 7, 29)

dtoverlay=i2c4,pins_6_7 (board pins 31, 26)

dtoverlay=i2c5,pins_12_13 (board pins 32, 33)

dtoverlay=i2c6,pins_22_23 (board pins 15, 16)

pi@raspberrypi:~ $ ls /dev/i2c*

/dev/i2c-1 /dev/i2c-3 /dev/i2c-4 /dev/i2c-5 /dev/i2c-6

Appendices

Appendix A - Rpi4V raspbian 10 buster Python 3.7.3 Multiple I2C Channel Testing Notes

# fi2c62.py  tlfong01 2019aug28hkt1433

from time          import sleep
import             smbus
import             fprint53    as fprint
import             ftime53     as ftime

# I2c Bus Setup Notes
# pi@raspberrypi:~ $ date Wed 28 Aug 2019 03:26:24 PM HKT
# pi@raspberrypi:~ $ uname -a
# Linux raspberrypi 4.19.58-v7l+ #1245 SMP Fri Jul 12 17:31:45 BST 2019 armv7l GNU/Linux
# pi@raspberrypi:~ $ sudo nano /boot/config.txt
# dtoverlay=i2c1,pins_2_3  (board pins 3, 5)
# dtoverlay=i2c3,pins_4_5  (board pins 7, 29)
# dtoverlay=i2c4,pins_6_7  (board pins 31, 26)
# dtoverlay=i2c5,pins_12_13 (board pins 32, 33)
# dtoverlay=i2c6,pins_22_23 (board pins 15, 16)
# pi@raspberrypi:~ $ ls /dev/i2c*
# /dev/i2c-1  /dev/i2c-3  /dev/i2c-4  /dev/i2c-5  /dev/i2c-6

# ********************************************************************************
# ********************************************************************************

# *** I2c Bus Config ***

i2cBus1 = smbus.SMBus(1) 
i2cBus3 = smbus.SMBus(3)
i2cBus4 = smbus.SMBus(4)
i2cBus5 = smbus.SMBus(5)

i2cBusDict = {'I2cBus1': i2cBus1,
              'I2cBus3': i2cBus3,
              'I2cBus4': i2cBus4,
              'I2cBus5': i2cBus5,
             }

# *** Pca9685 I2c Slave Device Congif ***

pca9685DevAddrDict = {
                'Dev0': 0x40,
                'Dev1': 0x41,
                'Dev2': 0x42,
                'Dev3': 0x43,
                'Dev4': 0x44,
                'Dev5': 0x45,
                'Dev6': 0x46,
                'Dev7': 0x47,
              }

pca9685RegAddrDict = { 'Mode1': 0x00,
                       'Mode2': 0x01,
                     }

pca9685DataByteDict = {
                       'Mode1Reset': 0x11,
    
    }

# ********************************************************************************
# ********************************************************************************

# *** Read Write Print Device/Register Functions ***

def writeDevTwoBytes(i2cBus, devAddr, writeByte1, writeByte2):
    i2cBus.write_byte_data(devAddr, writeByte1, writeByte2)
    return

def writeRegOneByte(i2cBus, devAddrDict, devName, regAddrDict, regName, writeByte):
    devAddr = devAddrDict[devName]
    regAddr = regAddrDict[regName]
    writeDevTwoBytes(i2cBus, devAddr, regAddr, writeByte)
    return

def readDevOneByte(i2cBus, devAddr, readByteAddr):
    readByte = i2cBus.read_byte_data(devAddr, readByteAddr)
    return readByte

def readRegOneByte(i2cBus, devAddrDict, devName, regAddrDict, regName):
    devAddr = devAddrDict[devName]
    regAddr = regAddrDict[regName]
    readByte = i2cBus.read_byte_data(devAddr, regAddr)
    return readByte

def printRegOneByte(i2cBus, devAddrDict, devName, regAddrDict, regName):
    readByte = readRegOneByte(i2cBusName, devAddrDict, devName, regAddrDict, regName)
    print(printTitle, hex(readByte))
    return
    
# *** Main Test Function ***

def testWriteReadPca9685Bus1Dev0RegMode1():     
    fprint.printBeginExecFunction()

    i2cBusName = 'I2cBus1'
    devName    = 'Dev0'
    regName    = 'Mode1'
   
    #i2cBus      = fi2c.i2cBusDict[i2cBusName]
    i2cBus      = i2cBusDict[i2cBusName]
    devAddrDict = pca9685DevAddrDict
    regAddrDict = pca9685RegAddrDict  
 
    writeByte = 0x77
    
    writeRegOneByte(i2cBus, devAddrDict, devName, regAddrDict, regName, writeByte)
    readByte = readRegOneByte(i2cBus, devAddrDict, devName, regAddrDict, regName) 
    
    if readByte == writeByte:
        resultsString = 'Good'
    else:
        resultsString = 'Bad'

    devAddr = devAddrDict[devName]
     
    fprint.printTitleOneByteNum('PCA9685 I2C Address',             fprint.indentFormat640, devAddr)
    fprint.printTitleOneByteNum('PCA9685 MODE1 Register Written',  fprint.indentFormat640, writeByte) 
    fprint.printTitleOneByteNum('PCA9685 MODE1 Register Read',     fprint.indentFormat640, readByte)    
    fprint.printTitleString('Write/Read Results',                  fprint.indentFormat640, resultsString)
 
    fprint.printEndExecFunction()
    return

def testPingPca9685Bus1Dev0RegMode1():     
    fprint.printBeginExecFunction()
    
    i2cBusName = 'I2cBus1'
    devName    = 'Dev0'
    regName    = 'Mode1'
   
    #i2cBus      = fi2c.i2cBusDict[i2cBusName]
    i2cBus      = i2cBusDict[i2cBusName]
    devAddrDict = pca9685DevAddrDict
    regAddrDict = pca9685RegAddrDict
    
    devAddr = devAddrDict[devName]
    
    readByte = readRegOneByte(i2cBus, devAddrDict, devName, regAddrDict, regName)    

    compareByte = pca9685DataByteDict['Mode1Reset'] 
    
    if readByte == compareByte:
        resultsString = 'Good'
    else:
        resultsString = 'Bad'
        
    fprint.printTitleString('PCA9685 I2C Address',             fprint.indentFormat640, hex(devAddr))
    fprint.printTitleString('PCA9685 MODE1 Register Written',  fprint.indentFormat640, hex(compareByte)) 
    fprint.printTitleString('PCA9685 MODE1 Register Read',     fprint.indentFormat640, hex(readByte))    
    fprint.printTitleString('Ping Results',                    fprint.indentFormat640, resultsString)
 
    fprint.printEndExecFunction()
    return
   
# ********************************************************************************
# ********************************************************************************

# *** Main Tests ***

def mainTests():
    #ftime.testPrintDateTime()
    testPingPca9685Bus1Dev0RegMode1()
    testWriteReadPca9685Bus1Dev0RegMode1()
    return
    
# ********************************************************************************
# ********************************************************************************

# *** Init/Main Functions ***

# *** Init Function ***

def init():
    pass
    return

#*** Main Function ***

def main():
    init()
    mainTests()    
    return

# ********************************************************************************
# ********************************************************************************

# *** Main ***

if __name__ == '__main__':
    main()

# *** End of Program ***

# ********************************************************************************
# ********************************************************************************

End of answer

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