x2dz
While I disagree with your over regulation of your dog, and some of your interesting thoughts on bacteria in standing water, based on my observations of our cat, the sheep and cattle in our paddock.
This is besides the fact that in the reply two up they weren't going to be in the hands of the Arduion god for more than 2 hours.
I've had lots of pets over my life, and haven't managed to kill one yet, but I blown up the odd electronics.
They usually make noise too, (sometimes it sounds like a relieved sound).
Transistors and FEts are different beasts.
Your drawing shows Fets with the internal clamping diodes. These provide both 'flyback' and overvoltage limiting.
The idea is that when an inductive load (relay) is de-energised the collapsing magnetic field induces a voltage in the coil windings.
This voltage is opposite to the original (antiphase/reverse...) and depending on the inductive load can be as high as the energising voltage. It wants to go somewhere and since it came from the relay, it ain't going back there.
The power supply capacitors act as a short circuit to this voltage (remember its the wrong way around, and a short duration spike) and low and behold the little old transistor/Fet is open and waiting for a reverse voltage, that usually exceeds it rating (for reverse voltage).
Usually the voltage spike is very short duration, and creates havoc on the supply line, upsetting the electronics. Often the bypass capacitors can't cope. (see below about the lack of them). So stopping it before its created is always good.
The diode across the relay coil will short out the induced voltage before its created.
The clamping diode across the transistor protects the transistor/fet, and the voltage (current as a result of the voltage) gets absorbed back into the coil, after it goes around through the capacitors and through the flyback.
Either one does the job.
second point
the power supply section seems to be lacking any sort of filtering (much like that horrible bucket smoothing out the water)
You need both larger values of capacitor and the 0.1uF ones as well. The rule of thumb is 1000uF for every 1Amp the circuit will supply, so add up those relays and make sure you have enough filtering.
Unlike the dog, electronics will only use what is needed, so you can go overboard, but doen't forget the 0.1uF as well.
general point
I tend to use an optocoupler on the output of the uP. Over the many years in the electronics game, I have noted that whenever something goes wrong, the transistor always dies. if you are lucky its between collector and emitter, but since murphy always appears, the base also gets clobered.
If the base gets clobbered the poor old uP (or other delicate electronic bit) usually receives a smack as well.
So I try to avoid this.
If you were concerned with running wires everywhere, the otion of a remote unit using an optocoupler and transistor/fet/triac on a seperate board is also avalable, and you only need to feed the 5/3.3v signal out.
Now that we are back into health care for animals....what exactly are your qualifications in regard to animal husbandry/vet/animal care (not sure if the same term is used overseas).
And btw from my life experiences, its often the people with money that don't look after their pets as well as those without money...come to think of it their cars and kids could almost be in that same boat.
i also recall reading somehwere that the old cowboys (we never had them here, they were all young) usued to eat poorly and drink water that was less that ideal, and then when they reached town, drunk lots of spirits, which neutralised the bateria.
Perhaps there is something in the mystery of why my cat prefers to drink from a manky bowl outside that could probably grow penicilin, rather than his fresh cleaned (yes we do actually wash it, but not in the dishwasher) bowl in the kitchen.
Perhaps hes topping up before cleaning out my booze cabinet.
Mark