I have a project with a small heating element, temperature controller, LCD readout, and input buttons. When I breadboarded it it worked fine, I upgraded it to a more permanent enclosure with the heating element and arduino powered by the same 9v 2A DC adapter. I’ve debugged everything else and it works fine, but whenever the heating element comes on, the LCD flickers badly, starts displaying gibberish, the temperature readout is fixed at 85 C, and the heating element just keeps heating up (a little strange since the relay is normally off). When I connect it with USB it works perfectly.
I think the heating element is drawing too much power from the power supply away from the arduino, when it is heating it draws 2.7A and the arduino supply voltage drops from 9V to 5.2V. (on a side note the power supply reads out 4.2A instead of the printed 2A, is that normal or is it mislabeled?)
I am pretty new to electronics, any suggestions how to keep the voltage from dropping so much for the arduino? A resistor for the heating element?