How to connect some sensors to motherboard?

Hi,

I know nothing about electronics but know something about programming 'office' applications.

My idea of a project is to have a computer (it may be a cheap ARM board) where I can install Linux (to have network connectivity) and have it to control watering.

So, I'd need some moisture sensors like these: **broken link removed**
(or other)

and also some water faucets (with electro valves?) to water the parts that are drier.

So, if there are ten sensors and four water faucets, how can I connect all these to a computer?

I know there are professional watering systems, but would like to build my own, because of customization and also of price, as well as satisfaction for doing such a project.

Connect the moisture sensor(s) analog input to the analog input port of the microcontroller.The new microcontrollers these days have an inbuilt analog to digital converter(ADC) so you need not buy one.Next connect the faucets to digital output port(s) of the microcontroller.And to help the microcontroller to do what needs to be done,and when should you do it,write a code for it and burn it in the program memory of the microcontroller.
Check again the system requirements to see that do you really need ten moisture sensors?Mostly microcontrollers have one or at most two analog input ports.You will need to multiplex them all,if you are going to use 10 inputs.

The cheap Chinese hygrometer has a pcb that will corrode soon in moist soil and it detects the conductivity of the soil, not its moisture content.
Conductive soil can be fairly dry but have a lot of conductive salts. The soil might be soaked with pure water but might not conduct.

Why do you need a computer? The hygrometer has no detailed datasheet so nobody knows what its "analog output more accurate" is for.

Things like electronic valve to turn the water on/off are normally driven by mains voltage (as used in every domestic washing machines). This means you need some way to get your computer with its 5V X .001A output to switch mains SAFELY. The only way is to use a relay, this is an electromechanical device that operate a switch, so 2 watts of low voltage can switch 2KW of mains voltage. So you will need some sort of amplifier/interface to get your 5V .001A to operate a 12V 100 mA relay, whose contacts can handle the mains voltage and current. Which should be pretty low as the valve only takes, say 5W or .02A. Somewhere you will have to find a DC power source for this, it could be you can find a 5V relay and power it from the micros supply.
The next advance is to use a Solid State Relay this is a module that accepts, say 5V at .02 A and switches mains. The mains and the 5V connections are fully isolated. It is doubtful if you can drive one direct from your micros out, so a 5V amplifier will be required.
For geeks only , you build your own SSR, with a triac and other components. This is not trivial as you don't want any mains to get back to your micro and yourself!
Frank

For less troubles,less expenses try arduino ^^