Reset NodeMCU master from Arduino slave

Question

I designed a PWS (personal weather station) which will be placed in a difficult to access location. In case of the master crashing and not requesting from the slave for a certain amount of time (stay alive protocol), is it possible to reset the master from the slave by powering a digital pin?

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Note, I improvised a pull down circuit so that the Arduino Nano's D7 (or any other digital pin) 5V output could be pulled down to 3.3V.

• Juraj: for me it didn't work for Wemos D1 mini. with level shifter it worked. I don't know why. but you should have a level shifter for esp8266 RX too
• tony gil: care to elaborate into an answer? tks @Juraj
• Juraj: I plan esp-01S wiring experiments this weekend and the reset of the esp8266 from Arduino is one of the goals
• aaa: The "RST" (reset pin) should work, try it w/o the other device, to see if it actually resets.
• tony gil: @Juraj da man! tell me how that goes, please! Do you want me to post this fritzing diagram as an fzz somewhere?

Answer 1

There is no need for a voltage divider or a level conversion on the reset pin of the esp8266. The esp8266 has internal pull-up on reset pin. To reset the esp8266 the reset pin must be connected to ground for a very short moment.

To pull the reset pin LOW with pin of the other MCU we do:

void resetEsp() {
 pinMode(ESP_RESET_PIN, OUTPUT);
 delay(1);
 pinMode(ESP_RESET_PIN, INPUT);
}

ESP_RESET_PIN is the pin wired to reset pin of the esp8266. It is not configured in setup() and it is never set HIGH (we don't want to send 5 V to esp8266). Setting the ESP_RESET_PIN to OUTPUT connects it to ground, setting it back to INPUT hands the control of the line back to esp8266 reset pin's internal pull-up.

• tony gil: not sure i understand the wiring. Does that mean that my Arduino (MCU) digital out is connected directly to NodeMCU RST pin? If not, do you mind posting a Fritzing diagram? UPVOTED pending clarification for eventual ACCEPT AS CORRECT ANSWER.
• tony gil: i am posting a Fritzing as an answer, please comment if correct or incorrect. Vote (up or down) if you will.
• Juraj: yes direct connection, because there is never 5 V from Nano side. it only pulls the reset LOW
• tony gil: ACCEPTED, tks!!

Answer 2

As per verification from Juraj, this would be correct wiring for his answer:

enter image description here

• Juraj: the point of reset from other MCU is not in wiring, but in code.
• tony gil: so is my original diagram correct, with the voltage divider?
• Juraj: I removed my comments about level conversion on I2C following Majenko's explanation here: arduino.stackexchange.com/questions/67461/…
• Juraj: as I write in the answer you don't need voltage divider on reset because it has nothing to divide. there is never 5 V
• Juraj: yes. of course there is a risk that some other unintentionally to Nano uploaded sketch sets the pin as output high.