That is too much confusion, let's investigate this :P
The Megapoints Controllers use the I2C bus as a "network".
There is a CAN board, but the MegaPoints Controllers use I2C.
In the video he uses 4k7 pullup resistors.
In his document he mentions that with a driver a cable length of "a kilometre" is possible.
He writes that on page 6 of his Network Guide.
He also writes there that those bus extenders are "fit for our purpose". That indicates that he definitely uses them.
For the 1km claim, he refers to the NXP Design note.
In that document on page 5, slide 10, it says that 2 meters is the maximum length for a normal 400kHz I2C bus.
On page 25, slide 68 is the 1km mentioned with 31kHz and I2C bus extenders such as the P82B715 and the P82B96.
I can not see a I2C bus extenders on the photo of the controllers :o
So I assume that the SDA and SCL of the ATmega328P chip are used.
The long cable is achieved with:
- 4k7 pullup resistors. I don't know if the 10k pullup on the Controllers is enabled with jumpers.
- I think he has GND between the SDA and SCL, that is very good.
- Perhaps a lower I2C clock.
- The garden is a very clean environment.
- Using only ATmega328P with their ridiculous high sink current up to 30 or 40mA. Some sensors can only sink 3mA, so he has no bare sensors in the network.
With or without those I2C bus extenders, I think it is possible.
So Mister MegaPoints has no secret after all, but I would like to see the software for the I2C bus ;)