So I am struggling with a problem, i am sure someone would have faced. I have a RAMPS shield with a arduino Mega working as the brain of my printer
Temperature readings from the heater thermocouple are noisy. The tuning process is on from last couple of hours.
1) When the atmega2560 is powered from the USB of the phone charger, the Vcc is 5.01 V. The temperature is very very stable and shows the same as my room temperature read from a mercury thermometer, which is 29C.
2) When the usb is disconnected, and 12 v supply from ramps is brought in, the voltage is stable at 4.98v. Temperature readings from Marlin vary from 29C to 34C and changes every second. When powered from the 12v from a 20a power brick, why should the temperature vary so much?
There is actually no temperature table for a thermocouple. The temperature is linearly related to the output of the ad595 TC chip. Is the noise of the switching supply somehow coupled to the 5v, so that the adc reference is noisy? Will adding a capacitor to the 12v output on the 5A rail clean this up?