hydroponically grown plant ,need help

Thread Starter

abhimanyu143

Joined Aug 25, 2014
211
I am reading some papers ,To become expert I think, I have do some practical work
I want to experiment for testing conductivity of water
just for my understanding I want to do some practical
I am using following material
multimeter
battery 12 v dc
2 glass
water
2 spoon sugar
2 spoon salt
two electrode
its enough or I am missing something ?
I can measure conductivity of single nutrient but the question is how to measure conductivity of different nutrients that are in water ?
 
Last edited:

wayneh

Joined Sep 9, 2010
17,496
You need n equations to solve for n unknowns. A conductivity analysis puts you at n=1.

If you want to distinguish the solutes, you need more tests. Refractive index is an easy one that can be done online. Freezing point depression is another one that measures the colligative properties of water.

I would imagine soluble nitrogen is fairly important but I don't know how they measure it. It's a lab test is my experience and I don't know if there's an online test. It wouldn't surprise me if the old-timers run on taste. I've seen that used in far uglier processes than hydroponics.

One point you may be missing is that the mineral nutrients are cheap and very dilute. You would need a very large installation before you could afford to spend much money on optimizing their use. It's far more practical to simply add nutrients to the fresh makeup water according to a recipe and let the recycling hydroponic feed solution go to the sewer at some bleed rate. Once that is set up properly, a few dollars of nutrients will supply a LOT of plants.
 

Thread Starter

abhimanyu143

Joined Aug 25, 2014
211
How to measure conductivity of nutrient that are in water ?
I am using micro controller, two pins of microcontroller are connected with two electrode
just for example I have 1 glass of water with Nitrogen than I can measure conductivity of Nitrogen . but If I use 1 glass water with Nitrogen and Phosphorous then how can I measure conductivity of two nutrient with two electrodes that are connected with microcontroller?

we have only two electrode pins that are measuring conductivity of many nutrient I am not sure that the two electrode can measure conductivity of many nutrient .

I can measure conductivity of single nutrient but the question is how to measure conductivity of different nutrients that are in water ?
 

wayneh

Joined Sep 9, 2010
17,496
You can't. It's that simple. You cannot solve for n unknowns with any less than n equations. Measurements like refractive index, conductivity, or osmolarity are very useful if and ONLY if you already know the approximate composition of the solutes in solution.

You need ion-selective probes or other analytical methods to determine the composition. For a small operation, it's not worth the expense.
 

Thread Starter

abhimanyu143

Joined Aug 25, 2014
211
Plant growing in water with mixed of liquid nutrient

Requirement
Water
Fertilizer

Best time to Fertilize
Plant grow from seed we need to Fertilize plant after their active growth
For better growth , we need to provide right Fertilizer at right time on basis of plant sie , weather, deases
Example- on the basis of plant size
Small plant need less Fertilizer
Large plant need more Fertilizer

Its all about agriculture site

Now from electronics site.
I want to make automated system that take decision , Add more or less Fertilizer into water .
If the plant require less or more Fertilizer the system can adjust itself
How to make automated system that will take decision Add more or less Fertilizer into water?
 

wayneh

Joined Sep 9, 2010
17,496
Start with one sensor, probably conductivity. Use that as a proxy measurement for all nutrients in solution. Design a nutrient addition system that will add small amounts of a nutrient concentrate into the system to maintain the conductivity within a range. You will need to be careful to add small amounts slowly enough to allow the system to respond, and to shut down and add nothing if any faults occur. Plants will be fine with just water for a long time, but can be killed quickly by an overly rich medium. Expand your control system as warranted, after you get this phase working.
 

GopherT

Joined Nov 23, 2012
8,009
The three major nutrients are potassium (K), phosphorus (P) and nitrogen (N). Various combinations of potassium, phosphate and nitrate salts are used. All will make a conductive solution in water. The problem comes when urea is used as the nitrogen source. Urea does not make ions in water but dissolves as a molecule. Therefore, it does not change conductivity and cannot be sensed with your simple system.
 

tcmtech

Joined Nov 4, 2013
2,867
I don't see where the precision of a micro controller systems would do any good being the natural ' process control loop' of growing plants can be days at a time between distinguishable input/output changes. :rolleyes:
 

Thread Starter

abhimanyu143

Joined Aug 25, 2014
211
The three major nutrients are potassium (K), phosphorus (P) and nitrogen (N). Various combinations of potassium, phosphate and nitrate salts are used. All will make a conductive solution in water. The problem comes when urea is used as the nitrogen source. Urea does not make ions in water but dissolves as a molecule. Therefore, it does not change conductivity and cannot be sensed with your simple system.
we can measure conductivity of whole solution. we can't measure separate the conductivities of different nutrient solved in water
for example we can not measure the separate conductivity of potassium (K), phosphorus (P) and nitrogen (N). but we can measure conductivity of whole solution In water.
how to measure conductivity of whole solution in water without conductivity sensor ?
I have listed some component That can I use
water , NPK Fertilizer ,multimeter , two electrodes
 

Thread Starter

abhimanyu143

Joined Aug 25, 2014
211
Start with one sensor, probably conductivity. .
I did google for conductivity sensor. I can't buy conductivity sensor. I can't effort conductivity sensor because the price is too high for me
I am not sure but I think I can use following component for conductivity measurement
water , NPK Fertilizer ,multimeter , two electrodes

Use that as a proxy measurement for all nutrients in solution
How to do Proxy measurement for all nutrients in solution

Design a nutrient addition system that will add small amounts of a nutrient concentrate into the system to maintain the conductivity within a range .
Its not easy for me. give me any Idea how to design system with electronic component
 

GopherT

Joined Nov 23, 2012
8,009
Option 1

Make a home- made sensor with two copper wires that are held at 1 cm distance.

Connect one sensor wire to an output pin on the Microcontroller.
Connect the other sensor wire to a 1k ohm resistor.

You now have a voltage divider. The voltage you measure across the 1k resistor will change as the resistance across the home made conductivity sensor changes.

Use the ADC on the Microcontroller to measure the voltage.

Make up several concentrations of water/fertilizer (one should be lower, one near your target and one above) and plot a calibration curve.

You will have to use some logic (PID for example) to control your concentration as the sensor will measure at one rate and the fertilizer will dissolve/dissipate slowly.

You can turn the output pin on/off to reduce power consumption if battery operated. If power efficiency is not important, the sensor can be connected directly to the positive power supply (not greater than microcontrollers supply voltage).

Option 2
If you don't have a ADC on your Microcontroller you can charge a capacitor across the distance of your sensor and measure the time (with con-board timers) to calculate when capacitor triggers a HIGH on an input pin connected to the junction between sensor and capacitor. (Change that input pin to an output (low) to discharge the capacitor, then back to input)
 

wayneh

Joined Sep 9, 2010
17,496
I can't buy conductivity sensor. I can't effort conductivity sensor because the price is too high for me
If that's the case, then I would abandon the idea of an elaborate, automated control system. As I said earlier, only large installations would bother with that anyway. They rely on lab tests and standard operating (feeding) procedures.

For instance I would probably set up a simple manual feeding system based on a schedule. It's easy to control the water level because you can see it and measure it very easily. Most of the water you add to the system is to make up for evaporation and plant respiration. A small amount of water must be bled off to the sewer to prevent accumulation of ...anything. Excess nutrients or microbial byproducts could accumulate without some bleed off.

Maybe once a week you can add a small shot of nutrients to the water feed, perhaps 100ppm nitrogen supplied by a fertilizer mix containing micronutrients as well (not just NPK). This mix will be adjusted for the type of plants you are raising and the stage of their growth cycle. (For example, higher N for rapid leaf growth followed by reduced N to induce flowering.)

Your biggest risk is over-feeding, so you need some analytical method to test for one of the macro nutrients, so that you can avoid over-feeding. I think I would follow N, and I believe there are easy soil test kits for soluble N. I could be wrong - P or K might be easier - so do a little research. I have a handheld refractometer like a grape buyer might use. That might work as well for measuring total solutes in the plant feed system.

This comes back to your goals. Are you trying to raise plants or trying to find an application for your microcontroller?
 

shortbus

Joined Sep 30, 2009
10,045
You may want to do some more studying on hydroponics. The nutrient levels on hydroponics do not change as much/often as you are thinking. The nutrient level in the water is much higher than the actual level needed for the plants, and the bigger problems of hydroponics are accumulation of nutrient 'salts' in the growing medium over time and PH level of the solution. The PH level has to do with the ability of the plant to use the nutrients.

Most people just keep the nutrient solution in use for a length of time then change to plain water for a few days to flush the system and then add new nutrient solution. Nutrients aren't added to the solution as you are trying to do. There are many good books and even websites on hydroponics, and you are spending too much time on something that isn't even needed for successful growing.

Oops,Wayne types faster than me
 

Thread Starter

abhimanyu143

Joined Aug 25, 2014
211
And how did post #34 work out?
your explanation was very helpful . mr. Wayneh asked me in his post. so I was telling him


Make a home- made sensor with two copper wires that are held at 1 cm distance.

Connect one sensor wire to an output pin on the Microcontroller.
Connect the other sensor wire to a 1k ohm resistor.
which sensor are you talking ? are you talking about conductivity sensor? . we can make with two copper wires, battery ,
 

GopherT

Joined Nov 23, 2012
8,009
your explanation was very helpful . mr. Wayneh asked me in his post. so I was telling him



which sensor are you talking ? are you talking about conductivity sensor? . we can make with two copper wires, battery ,
I am talking about making one. Platinum or platinum plates electrodes would be best - something that doesn't build up any oxides when in water so long. Make something to support the electrode (wire) tips at 1 cm apart.
 
Top