Hey, I am just wondering if it is possible for me to send a digital power from my NodeMCU to arduino. What I want to do is send a high voltage (3.3 volts) from my nodeMCU to a digital input pin on my Arduino. Will the digital input pin be set as high or will it need a full 5 volts to be set as high?
Use a logic level shifter to be sure.
Look at the data sheet for the processor of your mystery Arduino. It will list the Vih or the voltage for an input logic high. Many of the 5V processors have a Vih of Vcc * 0.6 or 3.0 V. 3.3V should be read as a high on those processors, so level shifting is probably not necessary.