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Auto Plant Watering System

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jessey

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Hello everyone, I'm trying to design a project that will use a 16F877 or similar chip with onboard comparators. I am new to programming and have not used onboard comparators yet. I played around with a 16F84A about a year ago to use it for an automatic plant watering system that I was designing. I wanted a micro to turn on a pump to water a potted plant when two probes in the soil detected a resistance of about 18 meg ohm's and also to be able to detect when the plant was thoroughly watered and to shut off the pump. I soon found out that the pic couldn't detect that resistance level with any accuracy so I proceeded to write code to have the pic shut off the pump after it was turned on with a timer. That part of the project worked great and I did make a circuit board and installed it into a box and used it while I was away on vacation to water my plants.

Last week I was going through some of the questions that were being asked in the Electronic Projects Design/Ideas/Reviews of this site and I found the topic Automatic plant waterier. This is the question that was asked by laurag :
Posted: Tue Sep 02, 2003 8:16 pm Post subject: Automatic plant waterier

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


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Tansis provided this link www.tep.org.uk/upload/112 circuits/Word/circ34.doc which has sparked my interest again. Is there anyone here that has tried this approach with a pic with onboard comparators? I would be interested in a discussion with people in the know here to hear their comments about what they think, if the pic would be able to accurately read the moisture level of the soil using a comparator with any kind of accuracy and if they think it would deliver consistent results that would be suitable for a plant watering system application?

Any comments, discussions or help would be greatly appreciated.
Thanks....................jessey
I can also be reached at: [email protected]
 

Oznog

Active Member
jessey said:
I wanted a micro to turn on a pump to water a potted plant when two probes in the soil detected a resistance of about 18 meg ohm's and also to be able to detect when the plant was thoroughly watered and to shut off the pump. I soon found out that the pic couldn't detect that resistance level with any accuracy so I proceeded to write code to have the pic shut off the pump after it was turned on with a timer.
Right, 18 MOhm is way too high. But that's fixable. Just put in a good op amp to buffer it and you're done.

Just use a 10 to 22 MOhm resistor as a pullup. I would recommend you source the supply for the pullup off of a PIC output pin rather than the 5v rail, and only switch it on right before sampling and turn it off when you don't need it. The DC current (although in this case it's quite small) can corrode the probes. Stainless steel is also a good probe material.
 

williB

New Member
Olihou said:
Hello Jessey

Hope you have already completed the project. I have the same plan as you did. I have built a good sensor according to the advice of Audioguru:

http://www.electronics-lab.com/forum/index.php?board=2;action=display;threadid=789

What I would like to built now is the watering part -- could you give me some advice, such as the availability of the water valve suitable?

Thanks

Oli
how much water do you need ??
reason i am asking is if you just have a few plants to water ...just use a small 12V water pump..
 

Olihou

Member
Thanks williB.

I have been thinking of watering directly from water tap, therefore I would like to have a low-flow electric valve.

A water pump would be fine though I would need a tank then, right? I am not aware that there are 12v water pump around. Could you advise what are the likely places where I can get it?

To start with I would like to buy one good enough for just a one feet diameter pot.

Best regards,

Oli
 

williB

New Member
Olihou said:
Thanks williB.

I have been thinking of watering directly from water tap, therefore I would like to have a low-flow electric valve.

A water pump would be fine though I would need a tank then, right? I am not aware that there are 12v water pump around. Could you advise what are the likely places where I can get it?

To start with I would like to buy one good enough for just a one feet diameter pot.

Best regards,

Oli
the one i have in mind is a decorative water trickeling thingy which goes on a table..if i can find it i will take a picture of it..
it has a wall powersupply to 12V to waterpump..
 

Oznog

Active Member
Olihou said:
I am not aware that there are 12v water pump around. Could you advise what are the likely places where I can get it?
I would think an automotive 12V windshield wiper fluid pump will do fine, any parts store or probably even WalMart.
 

jrz126

Active Member
But would the washer fluid pump be able to stand up to the pressures of the tap water. In a car there is no pressure being exerted on this pump. (from what I understand is, he wants to directly hook it up to the water line)
 

Olihou

Member
Hello jrz126, Oznog and williB

Thanks a lot for your input.

I have not decided to use a pump or a valve. I may try both to see which one gives a better result. For low water requirement, a small pump from a water tank would be fine. For larger operation (which I intend to do for farm land) a valve connected to water tap seems to be a better approach.

I do share with jrz126's view that connecting a pump to water tap might not be feasible.

Cheers

Oli
 

williB

New Member
Oznog said:
Olihou said:
I am not aware that there are 12v water pump around. Could you advise what are the likely places where I can get it?
I would think an automotive 12V windshield wiper fluid pump will do fine, any parts store or probably even WalMart.
there ya go !!
perfect for the application.. :)
 

williB

New Member
jrz126 said:
But would the washer fluid pump be able to stand up to the pressures of the tap water. In a car there is no pressure being exerted on this pump. (from what I understand is, he wants to directly hook it up to the water line)
with the pump method he would have to have a seperate tank of water..
 
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