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gear 0.2
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uc:
This is my project.
Lets START:
My wife received a green house for here 60 years present from our children.
Now I finally erected it.
She is complaining that she is not able to visit our grandchildren due to all the “growing stuff” that needs water.
So my project is:
Step 1 (today)
1.   Power input: 220W AC
2.   Safety against electric shock.
3.   Individual valve regulated water injection for 10 units (several plants in one unit). Based on liter/day
Step 2 (future)
1.   Power input: 220W AC
2.   Safety against electric shock.
3.   Individual valve regulated water injection for 10 units (several plants in one unit). Based on moisture in the dirt.
Step 3 (future future)
1.   Power input: 220W AC
2.   Safety against electric shock.
3.   Individual valve regulated water injection for 10 units (several plants in one unit). Based on liter/day optimized for moisture in the dirt and monitoring and regulated  via apps.
Step 4 (Future Future Future)
1.   Power input: 220W AC
2.   Safety against electric shock
3. Make nice happy plant LEDs so your wife knows which pots are hydrated... preferrably changing colors every few seconds on a 3d printed sunflower maybe? This will be icing on the cake

I was thinking to do a "Flowchart" for the Step 1 before I order any components.
Parallel, I will also follow "Mr Shock" advise to test the wiring  with a signal Sim. Refer to "gear 0.1
Could you guys give me some examples of "Flowchart".
Or is it a beter way ?
Do you gues have a idea how to sart a project without lose time?
Take care
//uc
Benta:
220W? Do you mean 230 V?
uc:
Yes sorry, |O wrong copy/paste. You are right.
rstofer:
The very first decision point is which solenoid valves.  How many volts, how much current, AC or DC?

From this you will come up with the design for a solenoid valve driver.  If the current is high or the solenoid is AC, you may want to use a small relay.  Here you need to pick the coil voltage so your electronics can deal with it.  12VDC seems reasonable and if the current is low enough, you can control it with a transistor.  You also need a reverse biased diode across the relay coil - Google for 'transistor relay driver'.  You could also use a Triac to control the AC valve - more study required...

http://www.edgefxkits.com/blog/relay-driver-circuit-using-uln2003-ic/

My goal would be to get voltages for the solenoid and relay that are reasonable and nowhere near mains voltage levels.  Maybe 24 VAC for the solenoids and 12 VDC for the relay coils.

Now all you have to do with the timer is trigger the transistor.  If the timer is capable, it could possibly drive the solenoid directly or maybe drive the relay.  Go to your local home center and look through the sprinkler timers.  So what they do.  Better yet, buy one with enough channels (I have 2 with 13 channels each) and see if they can be used somehow.  Or just repurpose the parts.

By all means necessary, stay away from mains voltages.  Make your gadget plug into a wall outlet, preferably with an external wall wart providing all the power.  If the wall wart is 12VDC, you can always drop it down to 5V for logic.
CatalinaWOW:
Setups to do this are widely available commercially in the US.  I assume this is also true in your country.

So the very first step is figuring out why you don't just purchase one.  You won't save money, but it is possible that you will incorporate features you can't buy or will enjoy the trip enough to make it worth while.  Determining which features you can't get in the commercial systems that you need or want will get you a long ways in defining your design.

You should also consider another path - start with a commercial system and then upgrade in steps as you propose with your own design.

Things to pick up from the commercial systems:

1.  They all use 24 AC volt solenoid valves with a step down isolation transformer to run them from the mains.  Logic/display circuitry power is also derived from this isolated 24 volt supply
2.  Most have battery backup so that watering program is not lost during any brief power interruption.
3.  Most incorporate a backflow prevention device to prevent contamination of the source water supply under a number of fault conditions.
4.  None that I have encountered has really solved the user interface problem.  Some are better than others, but there is real room for invention here.  Part of the problem is the limits on I/O caused by the low selling price.
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