I am a novice in electronics and Arduino. This will be my first project (a Plant Watering System) and I need some guidance:
- Is the schematic correct?
- Is the wiring correct?
- Are the parts chosen correctly?
Only one pump and one moisture sensor will be active at a time.
The first thing you should understand is that what you posted is not a schematic. Fritzing "breadboard" view diagrams are disliked by many forum members. But Fritzing does have a proper Schematic view, so switch to that, make it look neat and post that. +1 Karma for posting your links correctly (they are clickable).
My favourite tip for making a schematic neater is to use the "Ground", "5V" and "12V" symbols. Put as many as you like where you like so that you don't have as many criss-crossing wires.
Ok, mistakes I spotted so far:
Nano is a 5V device. You can't power it through the 3V3 pin. You could adjust the buck convertor for 5V and power the Nano through the 5V pin. Alternatively, you may be able to power it directly from the 12V supply and not use the buck convertor, but there is a danger of overheating the Nano's on-board regulator if too much current is drawn at 5V. With your circuit as shown, I don't think the current will be too much.
The soil moisture sensors have an analog output, but you show them connected to digital inputs. Maybe swap the pins with the ones currently connected to the MOSFETs.