• Why are ENV and Relay not working on the same port A?

  • @Kris The ENV unit uses I2C interface while the Relay unit uses a single bus (simple digital i/o) interface. For example, if you use M5Stack Fire, as default, the ENV unit is connected to Port A (I2C) and the Relay unit to Porb B (I/O). For some reason, if you really need to use Port A for your Relay unit, of course, you can. But you have to carefully program the correct pin of Port A to work as an output port to control the relay. To be more precise, the pin for SDA of (I2C) (yellow color) of Port A should be programmed to be an output pin (corresponding to the REL pin of your Relay unit). For this particular case, the fourth pin (SCL, white color) of the Port A is not used. The same grove cable can be used for both units. Good luck.

  • Check the pin layout of the two units:


  • I see.