I2C galvanic isolator

[mackowiakp]

The photo shows a galvanic isolator for USB 2.0 devices. Up to 5 kV security.
An interesting fact is that it isolates not only TX/RX signals but also the supply voltage.
Has anyone seen a similar device for the I2C bus?

Izolator.png

[Ath]

There are commercial I2C galvanic isolators available from f.e. Adafruit.

And if you own such USB-isolator, you could just try it, using 5V/3V3 level converters on both sides if it won't work with 3V3 (that it probably won't, is my guess). The basic principle looks the same. Possibly all the additional components could cause a bit of a delay so it might not work well at 400 kHz, but you could then probably still use it at 100 kHz.

[TD-er]

As you can see on the photo, the used isolator is from Analog Devices.
It is one from their "i-coupler" series.
They all start with "ADuM".
These are internally very similar to a "transformer" and have some circuitry surrounding them to brush up the signals.

There are several versions which mainly differ in the nr. of channels and their "direction".
The ADuM1250/ADuM1251 are for I2C upto 1Mbps. The ADuM2250/ADuM2251 for a higher isolation voltage.

The ADuM1250/ADuM2250 are probably the better choices as these have both SDA and SCL bi-directional, where the others have only SDA bi-directional.

The ADM3260 even has a DC/DC isolator (150 mW) combined in the same chip for a quite competitive price.

See the AnalogDevices page for their I2C series of isolator chips: https://www.analog.com/en/parametricsearch/11033#/
N.B. there are also "LTMxxxx" chips, but those operate using a different principle.

I think it is best to have these i-coupler chips connected to ESPEasy via an I2C multiplexer chip. This way it is actually a completely separate bus, electrically speaking (thus also need their own pull-up resistors)
These i-Coupler chips hardly introduce any delay, so that's not the reason to use an I2C multiplexer, but I don't know whether these may cause some kind of resonance when plugged into a longer bus which has other devices connected to it.

[mackowiakp]

OK, THX