OK here is a clearer explanation of what I am trying to achieve.
Firstly I want to dehumidify the air into water (or ice in this case). To do this I am using a peltier element. I will need to be able to switch this element on and off via the Arduino (hence the need for a programmable switch). I will need to measure the weight to know when the peltier has collected enough ice to be turned to water (switching the peltier off will immediately cause the ice to heat up and fall into the water collection tank.
Secondly, I want to convert the water to oxygen and hydrogen via electrolysis, I will need to measure the water level to make sure their is enough water to submerge the electrolytes (hence the measuring of water levels), and I will need to be able to switch the electrolytic process on and off (hence the need for a programmable switch).
My reason for doing this is "just because".
Well, all this kind of depends on whether you're doing this on an industrial scale (with industrial explosive atmosphere considerations), or at the kitchen sink with some old coffee jars.
I am not doing this on an industrial scale.
This depends upon the voltage and current of the electrolysis process. Or are you asking about how to do the actual electrolysis?
I am clearly not asking how to do the actual electrolysis, all I want to do is turn the process on and off via the Arduino. Voltage is 7.2 and current should be 500 mA (though I am open to the current varying to another up to 3A).
Same as above: what did you have in mind? My guess is that it's low-voltage high-current DC in which case a MOSFET would work, or a relay.
Peltier draws 3A from 10V of DC.
What kind of weight difference are you looking for? A change of a few grams, hundreds of grams?
A few grams.
This looks like a High School project and you want us to do your home work. That's fair enough -- some people love to help with those projects.
It is not a High School project.
PS: Do you know how to be safe with hydrogen? Is this a supervised project? You do know about explosives -- right?
I know how to be safe with hydrogen.
You do realize that you will supply more energy than you retrieve from the process -- right?