My college final year project requires some electronics ( which I don't really have a clue about!) which I could do with some help understanding.
It consists of a barrel within a barrel.
The inner barrel will contain food waste and cattle manure.
The outer barrel will contain water which will be heated with simple 2.2 kW kettle elements.
As the contents of the inner barrel must be kept at a temperature between 38-40 degrees Celsius, I have been instructed to use thermistors as the temperature measurement devices.
The thermistors will be connected to an arduino which will in turn control relays to power the elements on and off causing the water in the outer barrel to heat the inner barrel sufficiently, which in turn will be registered by the thermistors.
The elements will be ran off mains electricity.
I'll also include a 12V DC motor/stirrer.I was told to use a H bridge to control the speed.
My questions are as follows.
What kind of arduino do I need? (I'll be using maybe 8 thermistors and I know the ports are limited)
What kind of thermistors would be recommended?
How would I go about wiring this ? (breadboards needed etc.?)
Can the H bridge be connected to the arduino for control?
Taking in mind these are the cheapest options as I am running on a very tight budget!
I doubt that it is so critical, that you would need to take an average of so many. If it is critical, you would be better off using a single DS18B20. Come to think of it, it might be simpler to do that anyway.
sounds like you are making a double boiler. the heat in the inner barrel will be much more uniform because of the double boiler. also, with the stirrer, you probably only need two temperature sensors on the inner and two on the outer. maybe even just one on each.
Let me throw in a recommendation for a particular device to control a 120v device, up to 15 amps (1800 watts). The "Powerswitch Tail" is simply a small box with a male plug on one end, and a female one on the other end. On the side is a place to connect the signal, with can be any where between 3 and 12 volts. It basically puts all the dangerous voltage stuff inside, so you don't have to worry about it as much.
You seem to be seeking a lot of heating ability, with your specs of 2.2 kW. If you like the "Power Tail" product, you might use two separate heating elements, perhaps a 1500 watt, and a 750 watt one, and then power them separately. That way you can have a Low, Medium, and High level of power. (i.e. 750watt, 1500 watt, and 2250 watt.) I am working on a system now, where I need to control the heat of air in a chamber.
Are you sure you need that much heat? Remember that the methane digester will generate its own heat. If your outer barrel is insulated, then you may even find you need to cool the water, rather than heat it. You might cool it by bubbling air through the water from a fish-tank air pump, if that is needed.