I have an Arduino UNO and esp8266 connected to it. Both devices has separate power lines. Each connected via USB cable, for Arduino USB used as power line and standard firmware uppload line, for esp8266 only as power suppli line. If I connect all to computer's USB ports, everything working fine. But, if I connect Arduino to separate charger that has USB port, then Arduino not running code. I can see it by Serial interface work, because code using it intensively, and when I'm turning Arduino on the RX and TX lines are down all the time, that I think indicates, that code is not running, and Arduino in boot mode, somehow.

I've made a search through same issues and nothing helped from theirs suggestions. I tried to pull RX line to GND through resistor, to make sure that there are no noise on the line, added capacitors for power supply line, to make exclude pulsations on the line. But nothing helped.

Arduino not running code independently from esp8266. I tried to run Arduino separately, without any other connections, but it not helped. Still not running.

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    Diagrams would help ("a picture is worth 1000 words...") but it seems like everything regarding the ESP8266 can be removed from your question because at the end, you say: "I tried to run Arduino separately, without any other connections, but it not helped. Still not running." You didn't say exactly how you know it is not running. Overall, I suggest to simplify your test and clarify your question; add diagram / photos of minimum non-working config; remember not all "chargers" are good quality; this topic might be better moved to the Arduino SE, as they have more Arduino experience there. – SamGibson Dec 16 '16 at 13:00

This problem happened to me when I first started dealing with electronics.

Power supplies connected to the AC line usually have an "isolated transformer" inside them. What this does is both to lower the AC voltage down to a more operable AC voltage (which is then rectified to DC voltages) and also protect the user/equipment/(your house) in case of failure of the power supply (AC 230/110 V will seriously damage you!). You see, the transformer's output is "isolated" from the AC line.

Because of this, every power supply connected to the AC line has an "isolated/separate" GND and VCC level. So, if you wanted to power and use two or more PCB's together using separate power supplies, then you need to connect all of their (power supplies) GND's together so that you have a "common ground".

In your case, powering both "Arduino UNO and esp8266" from the same computer works because the computer is fed from a single power supply and that the computer's GND wires on the USB line are "common" i.e. not isolated.

When you power your Arduino from a separate supply, your Arduino and esp8266 has a different GND level so the RX and TX line between them must be floating. To solve your issue, connect a wire from Arduino GND port (it is next to Analog read pins) to Esp8266 GND pin (somewhere suitable, of course).


Have you made sure that the ground of both the arduino as well as esp8266 are connected together? Also since you are using esp8266 you must have connected it to rx and tx pins. Make sure you remove it while uploading the code and connect it afterwards.

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    Failure to provide common ground is almost certainly the reason. Connecting both devices to the same PC will most probably connect grounds together via USB GND. – Dmitry Grigoryev Dec 16 '16 at 9:58
  • This answer can apply in some cases, but it does not seem to fit with the last part of the OP's question: "I tried to run Arduino separately, without any other connections, but it not helped. Still not running." So if a separately-powered Arduino without any other connections isn't working (not clear how the OP decided that...) then missing ground connections between devices cannot be the cause, as they would not be needed when there is no other device involved :-) – SamGibson Dec 16 '16 at 13:06
  • @DmitryGrigoryev, Thanks a lot. This helped. Could you explain how? I have me own suggestions, but don't want believe them. – QuestionAndAnswer Dec 16 '16 at 13:49

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