user27485: I have a unidirectional communication from NodeMCU (ESP8266) -> Arduino UNO. The communication works when I power both the devices to my computer. Note that since it is from NodeMCU to Arduino only, I don't use a voltage regulator. However, when I use a battery supply 9V and connect to DC jack or 9V battery, the serial communication doesn't work. I tried even with the voltage regulator. 
It is mentioned that I use something between 9V-12V in the spec. Is it not working because 3.3V/5v from NodeMCU is not sufficient? How do I fix this problem?

Currently for the voltage regulator "high", I am supplying 5V from
Arduino. Should I provide another supply to pass 9v?
Does it power on if I provide 5V to DC jack or Vin?


user4143: 9V "transistor" (PP3) batteries are very weak. They barely provide enough current to power the Arduino, let alone a power hungry device like an ESP8266.
You're basically trying to tow a caravan with a skateboard.

27485: <p>I have a unidirectional communication from NodeMCU (ESP8266) -> Arduino UNO. The communication works when I power both the devices to my computer. Note that since it is from NodeMCU to Arduino only, I don't use a voltage regulator. However, when I use a battery supply 9V and connect to DC jack or 9V battery, the serial communication doesn't work. I tried even with the voltage regulator. </p>

<p>It is mentioned that I use something between 9V-12V in the spec. Is it not working because 3.3V/5v from NodeMCU is not sufficient? How do I fix this problem?</p>

<ol>
<li><p>Currently for the voltage regulator "high", I am supplying 5V from
Arduino. Should I provide another supply to pass 9v?</p></li>
<li><p>Does it power on if I provide 5V to DC jack or Vin?</p></li>
</ol>
 4143: <p>9V "transistor" (PP3) batteries are very weak. They barely provide enough current to power the Arduino, let alone a power hungry device like an ESP8266.</p>

<p>You're basically trying to tow a caravan with a skateboard.</p>
