When the motor is on, the measured temperature is 1 to 1.5 degree F lower than when the motor is off.
My DMM says the voltage of “A” (that powers the temp sensors and uC) decreases about 5 to 10mV when the motor is on (the last digit flickers…btwn 4.90v and 4.91v). A 13 mV drop would cause a 1 deg F decrease if the sensors weren’t ratiometric. But they are ratiometric, so that shouldn’t matter.
Here’s what I’ve done:
- The motor and uC+sensors are on separate power supplies (whose grounds are all connected).
- There is a capacitor at the motor.
- There are decoupling capacitors immediately adjacent to the 328’s power input pins.
- The power to the uC analog power pin and the temp sensors is from a LC filter.
- The temp sensors are an analog-type ratiometric sensor (Analog Devices AD22100)
- The temp sensors and motor are about four feet away from the uC
- The temp sensors and motor are on a “star” ground (their grounds meet near where all other grounds meet).
- Reported temps are an average of 64 readings, and they’re quite stable (vary about 0.5 deg F over an hour)
Not sure what else to do. Code is attached.
RootCellarDeployed4.ino (15.8 KB)