Connecting Arduino Uno to a Raspberry Pi

Question

Lets start with i'm a complete novice.

Pi Zero W: Used as a water level detector with the 3.3v and 3 GPIO pins soldered with some wires, that are spaced and attached to a pole, the 3.3v at the bottom and as the water increases/decreases it connects/disconnects the pins, which sends an alert with NotifymyDevice, runs on loop, as soon as the water level changes it sends an alert

Arduino Uno: Used as an Auto Feeder Has a 5v mini water pump, a moisture sensor, 5v relay, every hour the arduino checks the sensor and if the moisture level is low, turns on the pump for 1.5 seconds,

Wanted Outcome: When the feeder checks the moisture and if it has changed send a signal to the Pi which in turn sends a signal to NofitymyDevice, is it possible to connect the pi and arduino with a few connectors to get this done, if so could someone point me in the right direction, thanks

Answer 1

The nature of the signals you want to send are not clear.

I am going to assume you want to send a signal (without data) from the Arduino to the Pi.

The simplest way to achieve this end is as follows.

1. connect the Arduino and Pi grounds (i.e. connect a wire between an Arduino ground pin and a Pi ground pin).
2. Connect an Arduino GPIO to a Pi GPIO. This is not as straightforward as connecting a wire as the Arduino GPIO are 5V and the Pi GPIO are 3V3. One method is to use a couple of resistors as a voltage divider.
3. To send a signal toggle the Arduino GPIO on then off for a brief period. This can be detected by software at the Pi end to trigger any needed processing.