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I'm a really passionate beginner with arduino and electronics and I've built a Keypad lock for my room's door (inside the house).

I've used an arduino that activates a motor using a transistor to open the door if the correct pin is entered.

I want to add wifi control to my project. I have a few transistors, relays and ESP01s lying around for the upgrade. I want to use the blynk app and use the ESP01 independently without disturbing or modifying the arduino code. I'll program the ESP01 directly.

These are my requirements:

-A failsafe so I can open the lock via blynk if I forget the pin

-A kill switch that will turn off the arduino if I suspect somebody knows my PIN.

These are my ideas:

-Can I directly connect an ESP GPIO pin to the base of the transistor where the arduino is connected? By doing this can I control the transistor to switch the motor via both the arduino and the ESP 01?

-Can I put a relay module between the arduino and the battery pack and connect it to the ESP? I will connect the relay so that it will disconnect power to the arduino only when powered on. Is this a viable solution for a kill switch?

Any suggestions and ideas about how to go about this will be highly appreciated.

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Can I directly connect an ESP GPIO pin to the base of the transistor where the arduino is connected?

No. You will effectively be connecting two outputs together, and that is very bad.

Instead you will need to add a second transistor in parallel to the first - one controlled by the Arduino and one controlled by the ESP-01.

Can I put a relay module between the arduino and the battery pack and connect it to the ESP?

Sure. No problem with that.

I will connect the relay so that it will disconnect power to the arduino only when powered on. Is this a viable solution for a kill switch?

As long as the kill switch doesn't also shut off power to the ESP-01 - otherwise it will just switch on again straight away...

  • Thanks a lot. Can you please tell me about the parallel transistor arrangement in more detail? Also, how do I operate a 5V relay using 3.3v ESP01? Is it ok if I power the relay separately from the battery pack and only connect the signal pin to the ESP8266? – Pranav Jul 14 at 12:10
  • You can't drive a 5v relay from any microcontroller. If you have a relay module, not a relay, then it will most probably work. Otherwise you will be building a transistor driver circuit regardless of the voltage. – Majenko Jul 14 at 12:12

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