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Automatic plant waterier

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im designing an automatic plant waterier for a school project..but i cant seem to get the right electronic circuit!plz help!
it would have 2 prongs in the soil to check the dampness/dryness and when its recorded the soil is dry the circuits starts the water to water the soil. thats the plan anyway! thankyou kindly

In my limited experience with houseplants,
those that are kept wet or damp don't do as well
as those that get a little water daily, but not
enough to keep the soil damp, so it will dry out.

That cycle of drying out and getting wet seems to
be more to their liking, generally.

I have been told that if the soil doesn't dry out
it can lead to problems with various types of rot.

Not that i'm any expert.

A daily delivery of a given amount might be easier
to design.

John :)
If I were doing this I'd use several timers along with the measurement instrument described. One timer would accomplish the periodic watering as suggested though I had not thought about the wet/dry/wet cycle - makes perfect sense.

The other timer would simply be a limiter - maximum amount of water - so that if the probes were disconnected, moved, whatever, there would be some backup - otherwise the water might run forever.
I did this for a cabinet full of bonsi trees. After doing some research, I found that 40 seconds of water each day was perfect for the plants. Pot sizes, evaporation rate, amount of water delivered to each plant per second through the tubes, and water requirements for the plants was the key to the time decision. Then, the timer was connected to a small pump and set - no more concerns about watering.

A sensor to water the plant when it is dry will keep the plant damp but most plants don't want to be constantly damp and their roots will rot. A little research about the specific plants you are watering might reveal that they want to be watered once-a-week with 1/4 cup of water (for instance) and you can design your timer for that frequency/amount. The sensor project described previously might help with the research part of the project.
Here is a circuit to go with Tansis's circuit

Here is an analog circuit that I designed and tested that works great to shut off the pump after the watering starts. It uses two stainless steel machine nuts and bolts in the bottom of a drip tray to sense when the plant is watered thoroughly. I also wrote code for a 16f84a microprocessor to do the same thing and it also works great, I built a circuit board for the project and have the micro turning on a TIC246M triac instead of a relay to operate the pump. I used the micro circuit to water a plant from a timer and it worked great, the plant was still alive after a month while I was away on vacation. A person could feed the output of the comparator chip that tansis submitted into a micro and a when the right dryness level voltage was reached then the micro could turn on the pump and then the code I wrote could shut off the pump when the plant was watered thoroughly. I'm new to microprocessor programming but will check into it. You could use a 16f628 micro that has built in comparators. I was going to design a system that would check the resistance of the two probes in a soil and have the micro turn on the water when the soil was at the right dryness and then shut it off with the code I wrote, but that wouldn't work because the dry resistance of the soil was about 18 meg ohms of resistance and the micro can't read that high of a resistance with any kind of accuracy. I'll have to do some checking of what the comparators voltage would be at that dryness level (for the plant) and if the micro would read it accurately and if so then we could have an effective system here in either an analog version or a microprocessor version. I am just a hobbyist here and am very interested in coming up with a good system. I did have a spurt of energy to design a system and when it didn't look possible I shelved that part of the system and went with a timer and then moved on to other things. After finding this site, I stumbled onto this page and it has rekindled an interest when I seen the schematics that tansis submitted. I would be interested in what some of you people think of this idea and if there is anyone here that is into microprocessors that use the picbasic pro compiler or any other compiler for that matter with any experience in using the onboard comparators? Or anyone that has any other ideas for this kind of project. Thanks.............jessey

PS the transistors are hard to make out in the schematic so take note that the top of all transistors (pnp PN2222A) are the collectors and bottoms are emitters. Any scr could be used and the top is the gate and bottom is the cathode and the anode is grounded. The control signal in would be a 5 vdc transformer powered up by a timer or tansis's comparator circuit. I just forget what values I used for the resistors but I would say 1 kohm would do it. I hope this helps out.


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