Using the alternate I2C interface on HyperPixel 4.0

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1

The guidance on ‘Getting Started with HyperPixel 4.0’ doesn’t make it particularly clear how to get I2C to work.

The symlink example hasn’t worked on three different PIs:

By installing i2c-tools, I’ve checked available devices and get these for my latest install -

pi@CM4-2GB:~ $ i2cdetect -l
i2c-20  i2c             fef04500.i2c                            I2C adapter
i2c-21  i2c             fef09500.i2c                            I2C adapter
i2c-22  i2c             i2c@0                                     I2C adapter

So the guidance about i2c-3 redirect doesn’t work… a previous install had devices 10 to 12.

Also it would be helpful to state that i2c must not be enabled in raspi-config.

Hardware used: Pi3A, CM4 on Waveshare Nano Base Board (B) and Mini Base Board (B)
PiOS Bookworm 64bit and 32bit

2

I2C on the CM4 is not the same as I2C on the normal Pi. So this is not surprising.

There had been some conversations about this topic some time ago. I know that searching in the forums is not easy, but you will find something if you look hard enough. The conclusion was if I remember correctly that you could use the same I2C as the touch-controller, but you must bypass the OS-level access (i.e. /dev/i2c*) and communicate with the I2C-bus directly. For Python this is no problem.

3

Thanks for the reply bablokb. I have had success using the i2c with Python on all three computers I’ve connected to the display, including the Pi3A - which named it i2c-11. I’m using the non-touch model.

The reason for me posting was to give some feedback that the documentation could be clearer and more explicit.

For example:

To check the assigned address:

~ $ ls /dev/i2c*
/dev/i2c-20  /dev/i2c-21  /dev/i2c-22

The last listed device is the one to use. Check the python driver and utility tools are installed:

~ $ sudo apt install python3-smbus -y
~ $ sudo apt install i2c-tools -y

Then you can check the connected device is attached to the i2c bus:

~ $ i2cdetect -y 22
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: 50 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

Here is some sample Python code to check the bus is accessible.

init        = True
DEVICE_BUS  = 22
DEVICE_ADDR = 0x50

try:
    import smbus
    bus = smbus.SMBus(DEVICE_BUS)
except (ModuleNotFoundError, FileNotFoundError):
    init = False
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4

Thanks for sharing this Chris - a revised Hyperpixel getting started guide has been on my to-do list for a while but it’s been a very busy couple of months for us!

I’ll be sure to include this information when I get to it - is it OK if I link this post from the shop page in the meantime?

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5

Absolutely! :-) Information is to be shared

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