Arduino "is an open-source electronics platform based on easy-to-use hardware and software."
We will mainly speek about Arduino UNO.
Arduino is a microcontroller that can read environment data and interact with it.
Arduino is self alimented by USB.
It could also run from 6 to more than 12V.
The main voltage in our circuit will be 5V.
Circuits need ground 0V and +5V.
It comes with a development tools that allow you to write logicals programs, load it to arduino, read in another window the serial output.
Sensors can read environment data.
We use a light sensor to be able to know if the sun is shining or if the night is dark. It will also help us to detect if our "artificial" is lighted on or off when it should.
Water level sensor
We need to know if there are enough water in our tank. Water pump or worst moist maker could be damaged by a dry environment.
Temperature & humidity (DHT11)
We would like to know if temperature is not too high and humidity too low, moisture can develop if there is an high humidity level, red spiders like a temperature higher than 24°C and humidity under 50% ...
Aquarium water pump, air extractor fan, lights need high power voltage (230V).
Arduino cannot light on or off this kind of power, we will user load relays that accept 5V in input and are able to switch 230V current.
Arduino auto reset
Arduino reset itself when serial port is open, to disable auto-reset we can connect a 110Ohm resistor between 5V et Reset pins.