ATOM RS-485 - No power via USB

  • I've been using the ATOM RS-485n kit ( to connect to an electricity meter using ESPHome. Last night this was working with the A/B wires connected to the meter and the ATOM lite powered via the USB connection to my laptop.

    Today, for some reason, if I plug the ATOM lite into the RS485 unit then it won't power at all via USB whether or not the A/B wires are connected. I must be doing something different, but for the life of me can't work out what is different.

    Should I expect to be able to power it by USB? Is there something I might have done (software or hardware) that would stop that happening. The ATOM lite is still working - if I connect it without the RS-485 base then it works exactly as expected.

    Any suggestions very welcome!


  • Hello @watchforstock

    looking at the ATOM RS485 schematic the only way I see which would keep the M5Atom from powering up when plugged into the ATOM RS485 is if somehow the 5 V line is (partly) shorted to GND.

    Now, there is a built-in DC-DC converter in the ATOM RS485 converting the input voltage from the RS485 connector to 5 V. In your case however this DC-DC converter is not fed an input voltage. Maybe the DC-DC converter IC didn't like the fact it was fed 5 V into its output from the M5Atom.

    You could try to measure the 5 V on the Groove connector while the M5Atom is plugged into the ATOM RS485 to see if it somehow is pulled down.