RX/TX voltages for Atom Lite

andyb · Mar 6, 2023, 5:13 AM

Hi, new to this forum and a bit of a newbie to hardware-level hacking … so forgive me if I’m asking a stupid question.

I want to connect my air conditioning unit (mitsubishi heat pump) to our wifi network using an Atom Lite. The ac unit has a serial connector delivering 5V power and also using 5V signalling for RX/TX via a JST PA connector. To keep it neat, I was going to use a USB-C cable with breakout wires and a JST connector to wire them directly.

I’m aware that the PICO board in the Atom Lite uses 3.3V for signalling, but there appears to be a regulator in the circuit board diagram for the USB-C port. I think that means I can connect the ac unit RX/TX pins directly to the USB DP/DM wires.

Is anyone able to confirm?

In case it’s useful, I was planning to use esphome to flash the Atom Lite based on this code: https://github.com/geoffdavis/esphome-mitsubishiheatpump. The producer of the underlying arduino software noted the need for regulators for other ESP boards: https://github.com/SwiCago/HeatPump#other-part-suggestions.

Thanks.

ajb2k3 · Mar 7, 2023, 5:34 AM

from what im aware the pins are 3v3 logic and so you need a 5v>3v3 logic shifter board like this: https://www.amazon.co.uk/Youmile-Channels-Converter-Bi-Directional-Shifter/dp/B08BZ8K7YR/ref=sr_1_2_sspa?crid=1YGIYN9553SC8&keywords=logic+shifter&qid=1678167168&sprefix=logic+shifter%2Caps%2C74&sr=8-2-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1

between the M5Atom and the zircon unit.