SMC PSE 540 pressure sensor and Arduino/Genuino UNO power source problem

Hi Guys,

I’m using pressure sensor: SMC PSE540, with: Genuino UNO, board covered by: Arduino 4 Relays Shield, and I’m facing some strange behaviour based on used power source.

The sensor needs 12V to power, therefore I’m using external power sources:

  2. VOLTCRAFT FPPS 514211

I’m using them in two configurations:

  1. VOLTCRAFT PLUG-18W → USB plug to Genuino USB + 12V to the sensor

  2. VOLTCRAFT FPPS 514211 → 9V to Genuino power jack
    VOLTCRAFT PLUG-18W → 12V to the sensor

In case I power Genuino and the sensor just from VOLTCRAFT PLUG-18W (option 1) everything is working correctly.
In case I use the second option, input voltage from the sensor is giving me values, which are changing from minus to plus and are wrong.

The Genuino is covered by Arduino 4 Relays Shield and I’m also using JHD162A LCD SCREEN.
Please see the attached schemas and pictures.

Am I missing something obvious, can you please help?

Thank you!

It seems you didn't connect sensor ground (blue -) to Arduino ground (see first diagram).

If you use a supply with double outputs (12volt + USB), then grounds are probably shared inside that supply.

Perfect, that was it.

Thank you very much.
One can see, I'm not very good in electronics :frowning: