Hi, I am working on an espresso machine with Pressure sensor (0-5VDC) and 2 x MAX 6675 ( thermocouple ).
I use one power supply 220VAC to 24VDC to power the pump and use a 24VDC-->6.5VDC to power the Arduino.
If I power the Arduino with the same 24VDC power supply using for the pump:
1. The reading of thermocouple is couple of degree lowered than if I power the Arduino unit with Notebook USB
2. When I start the pump, the reading of thermocuple start will be 3 to 5 degree lower than when the pump is off.
3. I have measured the voltage apply to Arduino which is stable regardless of the pump status (6.5V)
4. The reading of the pressure sensor is correct
If I power the Arduino using the notebook USB power
1. The reading on the thermocouple is stable and correct
2. The reading on the pressure sensor is incorrect (which is normal as is not grounded with Arduino)
What's wrong with this setup?