Comments on: How to make a cheap soil moisture sensor

By: DIY Soil Moisture Sensor | The Express Art Blog

DIY Soil Moisture Sensor | The Express Art Blog — Wed, 10 Mar 2010 03:00:56 +0000

[...] automation on my side. When I was looking into what some other people had done I came across this DIY Soil Moisture Sensor on The Cheap Vegetable Gardener site. THERE is also lots of cool information on the site for [...]

By: DIY Soil Moisture Sensor - Hacked Gadgets - DIY Tech Blog

DIY Soil Moisture Sensor - Hacked Gadgets - DIY Tech Blog — Wed, 10 Mar 2010 02:39:54 +0000

[...] automation on my side. When I was looking into what some other people had done I came across this DIY Soil Moisture Sensor on The Cheap Vegetable Gardener site. There is also lots of cool information on the site for [...]

By: Joel Jose

Joel Jose — Tue, 02 Mar 2010 17:06:50 +0000

Sir basically i wanted the output of the sensor in voltage which will be send to the AVR microcontroller, then the output will be given to the LCD to display the percentage of soil moisture content. It is a third year mini project and i really need help since i have a presentation on 6th March and God gave me you. Could you guide me for the programming and how do i measure the output in voltage if not how do i program the code based on the resistance value.Please guide me. Does the value change with size of length.

By: The Cheap Vegetable Gardener

The Cheap Vegetable Gardener — Tue, 02 Mar 2010 16:57:20 +0000

Joel, how about I answer here so everyone knows the answer

If you make your own sensor it is probably best for you to calibrate it by getting a value of it dry and then a value after sitting in water for a couple minutes. That should be a good range to determine your various water saturation.

By: Joel Jose

Joel Jose — Mon, 01 Mar 2010 17:09:31 +0000

I needed the output in voltage to interface it to AVR controller. I have the synopsis just needed you to have a look could you reply to my e-mail i.d.

By: Joel Jose

Joel Jose — Mon, 01 Mar 2010 16:56:32 +0000

Amazing sensor, not tried yet will definately try it. I needed to discuss a project. I am planning to use the commercial sensor. could you send me your e-mail id for further discussion.

By: micropile

micropile — Mon, 15 Feb 2010 17:25:33 +0000

McGyver, eat your heart out!

By: The Cheap Vegetable Gardener

The Cheap Vegetable Gardener — Thu, 04 Feb 2010 16:49:58 +0000

I would probably recommend sticking to agricultural lime since plaster of paris does have some additional additives which I am not sure would have adverse effects on your lawn/environment

By: chet

chet — Wed, 03 Feb 2010 14:22:54 +0000

If you wanted to dump your left-over plaster might it be a good additive, like agricultural lime, for your lawn or garden?

By: ridatia

ridatia — Sat, 19 Dec 2009 17:58:36 +0000

If you try and measure it with a normal digital voltmeter, which uses DC excitation, then what you will notice is that the reading drifts continuously due to polarization of the block (movement of ions towards the electrodes).In all workable gypsum block resistance measurements, you need AC excitation to prevent this ionization occurring (if you keep changing the direction of the electric field, average ionic movement is zero).

By: fred070

fred070 — Fri, 27 Nov 2009 22:23:41 +0000

yeah, thanks for this useful blog. By the way, i would like to test my probes durability too. I've seen your revised cheap soil moisture sensor. I'll try that

By: The Cheap Vegetable Gardener

The Cheap Vegetable Gardener — Fri, 06 Nov 2009 01:35:21 +0000

AcmeUK, great idea. Effective, cheap and low voltage so less worries about electrocuting yourself.

By: AcmeUK

AcmeUK — Thu, 05 Nov 2009 15:54:23 +0000

Hey GuysInstead of looking for a cheap water solenoid (valve) how about using a windshield washer pump? they are 12v and cheap. OK the flow rate is not great but should be adequate.

By: The Cheap Vegetable Gardener

The Cheap Vegetable Gardener — Thu, 15 Oct 2009 15:46:43 +0000

fred, glad you got it working. I am sure I responded to a couple of your other questions before not sure what happened. So did you go with galvanized rods in the ground and skip the gypsum or rods in gypsum?

By: fred070

fred070 — Tue, 13 Oct 2009 01:32:07 +0000

thanks! i got a new answer.. i used 2 galvanized iron and it works great!

By: fred070

fred070 — Fri, 09 Oct 2009 16:11:17 +0000

if full saturated.. the value should drop down to zero right? zero resistance basis..

By: fred070

fred070 — Fri, 09 Oct 2009 16:09:49 +0000

thanks for the reply mr cheap vegetable gardener.. i would like to use to your arduino project for measuring the soil moisture (we have here at our country [philippines] (im)duino which is also an arduino based board.. im thinking.. where am i going to buy a vegetronix. since i'm dealing for the low cost project (such this cheap soil moisture sensor) it will take bunch of bucks out of my pocket just to deliver the vegetronix sensor from there. any alternatives for vegetronix? ok i'll read your linked article.. thanks for the help!

By: The Cheap Vegetable Gardener

The Cheap Vegetable Gardener — Thu, 08 Oct 2009 16:06:32 +0000

fred, well when metal and water combine rust will happen. Even with the rust the soil sensor remained accurate for the season (9 months) before I created a new version, which reminds me I should do a new write-up on it. Concept is still the same though used small galvanized nails and made the block a little bigger. Stainless steel is also a good option for probes.As for your measurements, that is true that you should have a range of 0 to 32767 though if you still have the stick attached or more importantly the potentiometer, which when centered is at the midway point 16383 so this in place you range is 16383 to 32767. So completely dry you should expect a value of 16383 and full saturated (basically sitting in water) a value of 32767. So you 19K number does sound in the right ball park if the soil is simply moist.If you want more accuracy you can try removing the potentiometer, though I chose to not mess with this so I can’t really help with the wiring. You may also consider using an arduino which is the method I am currently doing now, though the PS2 Controller worked fine I wanted to clean things up and move all my controls to a single component and for $30 pretty nice piece of hardware. Here is a write-up of my grow box controller using an Arduino.

By: fred070

fred070 — Wed, 07 Oct 2009 04:23:42 +0000

hello mr cheap vegetable gardener… i used this soil moisture sensor the the ps2 controller.. the metal i used in the soil moisture sensor is only a barbed wire.. and after few days.. in my experiment, the values are getting wrong..on my ps2 controller:32767 = max resistance0 = min resistance..i got 19967 value even it's wet..im expecting 1000 – 3000.. i double that the metal i used got rusted inside the gypsum block..

By: The Cheap Vegetable Gardener

The Cheap Vegetable Gardener — Wed, 07 Oct 2009 01:08:32 +0000

They spike when you first dump water on them (as they probably should) though they quickly (within a minute or two balance out when the soil absorbs it.

By: Leoanrdo

Leoanrdo — Tue, 06 Oct 2009 18:26:00 +0000

Hello people. This is exactly what I was looking for. Thanks a lot!!! I haven't build it yet though, my only concern is how long does it take to setle once you water the soil. And how is the relation between the soil ant the probe regarding the drying. I mean, once you water the soil, does the probe stay "wetter" than the soil? or does it act similar to the soil?I know I may not be very clear, please let me know if you don't understand my question.Thanks in advanced

By: The Cheap Vegetable Gardener

The Cheap Vegetable Gardener — Sun, 04 Oct 2009 06:13:23 +0000

Andrew, those sensors are great check how I used on this post where I used one with an Arduino

By: Andrew

Andrew — Thu, 01 Oct 2009 22:31:19 +0000

http://www.vegetronix.com

By: szilard

szilard — Thu, 24 Sep 2009 04:39:01 +0000

jwb7605 – the major reason for AC current is electrolysis, and electrolytic corrosion of and salt/crud buildup near one of the electrodes (anode, +, just like with car batteries, the red cable is the one always messed up, never have a problem with the negative black one). AC current is neutral in this sense – whatever ions from the metal force-corrode/pass into solution when the electrode is positive, are pulled right back out when the electrode becomes negative on the other part of the AC cycle. The net result is no pollution of the solution with foreign ions no corrosion/deterioration of the electrodes.

By: The Cheap Vegetable Gardener

The Cheap Vegetable Gardener — Sun, 20 Sep 2009 17:18:59 +0000

jwb7605, That is definitely a true statement using AC current does provide more accurate results though for my safety I avoid using high voltage when possible. The low voltage method though less accurate is much safer and easy to setup. Though accuracy all depends on your needs for me, I just need a general range when I need to turn on a water pump to water my plants so a percent or two is no big deal to me.

By: jwb7605

jwb7605 — Fri, 18 Sep 2009 14:21:51 +0000

I've read that you should be using AC for the signal (as in a low voltage transformer secondary), or the calibration begins to deteriorate and you get inaccurate results. You end up measuring AC voltage instead of resistance (and you'll need a resistor in series with the sensor — about 1K in your case — to pick the signal off of).Have you been using this long enough to validate or disprove that?GREAT blog, by the way.

By: The Cheap Vegetable Gardener

The Cheap Vegetable Gardener — Tue, 08 Sep 2009 16:15:32 +0000

Chip, I have experimented some this summer with a few different designs and size and distance does not appear to change the readings much. Though the type of metal (rust prevention) probably should be considered. Galvanized/stainless steal are definitely preferred.

By: Chip

Chip — Mon, 07 Sep 2009 16:03:49 +0000

I understand you used picture hangers for your electrical contacts. I wonder how critical the surface area of the electrical contacts in the gypsum is? I was thinking about using a standard 3 pin protoboard header instead of the picture hangers. It will definately hold it's shape and the metal ends are about 1/4 inch long and about 1/4 inch apart ( if you ignore the center post ). That and I have about a dozen of them in my tool box.

By: The Cheap Vegetable Gardener

The Cheap Vegetable Gardener — Sat, 05 Sep 2009 02:49:16 +0000

Freddie, depends on how you want to use it. You could hook it up to a PS2 Controller and check the resistence with it. Or basically any other device that accepts an analog input (basic stamp, arduino) If you stay tuned I will be providing some more info on how to do this with arduino.

By: Freddie

Freddie — Fri, 04 Sep 2009 01:55:02 +0000

Hi Mr. Cheap Vegetable Gardener.. I'm happy i saw this cheap soil moisture sensor.. I'm all about to this, but how am I going to measure its resistance without using the ohm meter or multi tester. Any alternatives?

By: The Cheap Vegetable Gardener

The Cheap Vegetable Gardener — Mon, 31 Aug 2009 14:47:26 +0000

Trav, glad it worked out for you. I have been very happy with them as well.

By: Trav

Trav — Tue, 25 Aug 2009 03:56:40 +0000

From anonymous up there:"0 resistance = short circuit, right?infinite resistance = no circuitwhich I think is what you'd be looking for, then the resistance going down to 975 when wet, 975 = wetter 1500 = dryer5000 = dryerinfinite = dust"^^^^^^That was about exactly what mine turned out to be. When bone dry I was getting in the 4 Mega ohm range…..and as it got progressively wetter the resistance went all the way down to around 250 ohms. I am surprised at the functionality and range of this probe.I used basic solid core wire, I used paper clips and spaced them about 1 mm from each other….this seems to yield the best result that I have found so far….+1 CVG, thanks for the great ideas, love the blog….

By: Anonymous

Anonymous — Thu, 30 Jul 2009 10:13:01 +0000

am trying to buid a soil moisture sensor.in the recent edn circuit designer contest,the second prize winner has constructed a wireless moisture probe wherein he has used the galavanic moisture probe to measure soil moisture content.according to the author"The galvanic probe is essentially a coaxial tube with a center rod, each made of dissimilarmetals. A galvanic potential is developed between the rod and tube, depending on the moisture5content of the soil.can i construct one such to measure soil moisture.

By: The Cheap Vegetable Gardener

The Cheap Vegetable Gardener — Thu, 09 Jul 2009 02:39:11 +0000

Bernado, the voltage divider is to decrease the amount of voltage going to the analog sensor. What you want to ensure is the maximum measureable voltage is at 100% not 50% so you use the resistor is used to reduce the total voltage to make a more accurate measurement.Burn, stay tuned I should have a more detailed write-up for what you are looking for.

By: jlindema

jlindema — Thu, 09 Jul 2009 02:37:31 +0000

CVG- awesome website!lanmat re: your post on May 22, 2009 6:46 PM I'm having the same problem finding cheap, electronically-controlled valves. This one looks promising:https://www.surpluscenter.com/item.asp?UID=2009063019314890&item=20-1306&catname=water(and cheap)

By: BuRn

BuRn — Tue, 07 Jul 2009 10:01:00 +0000

can you teach me in detail how to build my own automatic garden watering system using your moisture sensor in detail… i really interested (>.<)this is my email: fakaratuldeath@yahoo.co.uk

By: Bernardo

Bernardo — Thu, 11 Jun 2009 19:26:53 +0000

Thank you for your reply! Let me just ask you what is the purpose of puting a reistor between the other end of the sensor and the ground? I'm looking at Arduino, seems a little bit more complicated to interact with than phidgets, but thanks for the advice. It will eventually depend on my father, cause he is the one paying!

By: The Cheap Vegetable Gardener

The Cheap Vegetable Gardener — Thu, 11 Jun 2009 15:58:35 +0000

Bernado, I wouldn't recommend putting a humidity sensor under ground not sure if it would work…though would expect it would stop working after a few waterings.As for phidgets, there is no reason this wouldn't work with one of the analog inputs. Though to wire it you would need to create a voltage divider, basic idea hook up one end of sensor to 5V, other end up to analog sensor and ground. May also need to add resistor on ground/analog side to get better accuracy but not sure how accurate you need moisture content to be I have done something very similiar using Arduino (similar idea as phidgets but half the cost, I am the Cheap Vegetable Gardener) Hopefully in the next week or so I will post an update with some of my grow box improvments including addition of Arduino.

By: Bernardo

Bernardo — Thu, 11 Jun 2009 11:07:01 +0000

Great blog, I love it! I have several questions:1- Could you use a genreal humidity sensor instead? something like this:http://www.phidgets.com/products.php?category=1&product_id=1125Would it work or is it just for the atmosphere?2- If I build your moisture sensor, how could I connect it to the phidgets interface?http://www.phidgets.com/products.php?product_id=1018I love gardening and electronics, but I'm just 17, so my knowledge is rather limited (by the way, I live in Portugal, so i'm an international visitor!)Thanks in advance

By: Chris

Chris — Fri, 05 Jun 2009 04:26:21 +0000

So i guess we're just measuring the EC of the soil, but it still gives a general idea moisture content.

By: fletcherquark

fletcherquark — Fri, 05 Jun 2009 03:57:37 +0000

Ooops. Correction:1. How does the ECH2O probe measurevolumetric water content (VWC)?The ECH2O probes use capacitance tomeasure the dielectric permittivity of thesurrounding medium. The volume of waterin the total volume of soil most heavilyinfluences the dielectric permittivity of thesoil because the dielectric of water (80) ismuch greater than the other constituents ofthe soil (mineral soil, 4; organic matter, 4;air, 1). Thus, when the amount of waterchanges in the soil, the ECH2O probe willmeasure a change in capacitance (from thechange in dielectric permittivity) that can bedirectly correlated with a change in watercontent. Circuitry inside the ECH2O probechanges the capacitance measurement into aproportional millivolt output.sensors measure watercontent using a dielectric measurement; theEC-5, EC-TM, 5TE, and 10HS use ameasurement frequency at 70 MHz,compared to the EC-10 and EC-20 sensors atabout 10 MHz. Because of this increasedmeasurement frequency, the 70 MHz sensorsare almost completely insensitive todifferences in electrical conductivityhttp://www.decagon.com/pdfs/app_notes/FrequentlyAskedQuestionsAboutECH2O.pdf

By: fletcherquark

fletcherquark — Fri, 05 Jun 2009 01:34:27 +0000

"Real" moisture sensors use a.c. rather than d.c. to obviate polarization problems. They have circuitry to generate it. I wonder if the resistance readings don't get whacky after a while from the effects of polarization.See also…http://www.plantsense.com/http://www.decagon.com/Thanks for the write up. I'll have to play around with it (think I stuck some wire in gypsum board some time back but can't remember the results.)

By: Chris

Chris — Thu, 04 Jun 2009 15:08:41 +0000

yeah, you really don't need much. I'm using a Make Controller connected to a switch, with a 100' cat5 cable running to the router. The cameras are wireless.

By: The Cheap Vegetable Gardener

The Cheap Vegetable Gardener — Thu, 04 Jun 2009 04:51:31 +0000

Chris, awesome setup will have to check again when the lights are on. I need to setup some internet connectivity to my grow box, but unfortunately no internet in my garage.

By: Chris

Chris — Wed, 03 Jun 2009 20:09:04 +0000

thanks for the write-up, here's one in action.http://71.194.86.121:8080/ un: public pw: test

By: Anonymous

Anonymous — Tue, 02 Jun 2009 14:53:29 +0000

Thanks CVG for the probe descriptionlanmat, if you want a 12VDC system check out Intellitec.com for a pump controller to save your batteries. If money is not an issue check out the Rainbird TBOS 9VDC localized system.Anonymous or anyone, which microcontroller are you using? I want something with flash memory.Thanks,iri-gator

By: lanmat

lanmat — Sat, 23 May 2009 01:46:40 +0000

I’m also very interested in putting my flower beds and vegetable patches on an automatic Arduino-based solar battery-powered moisture feedback loop. Your sensor idea is similar to other’s I’ve discovered, but more well-thought out. I do have a question about regulators, though. I seem to luck out on finding any information on small (say 1/4″ tubing) localized solenoid valves for drip irrigation hoses. What do you use to switch your irrigation? The bulk of what I’ve seen are 24VAC 1″ tubing under-ground sprinkler solenoid valves. Any suggestions on what to use to control water flow for a given zone?

By: Anson

Anson — Mon, 18 May 2009 21:47:00 +0000

You could use copper wire but the picture hangers make it easier to fabricate and give convenient connection points.

By: Jay Buster

Jay Buster — Mon, 18 May 2009 19:50:00 +0000

Very cool!Would it make sense to use thick copper wire, with bare ends, inside of the probe?

By: Anson

Anson — Sat, 16 May 2009 19:35:00 +0000

I made one of these to monitor the soil in a hanging basket. I’m always letting it get too dry. My plant now tweets its status on twitter daily as feedmeseymour.