EC Probes - How they work, and how to build one.

I decided to take a look into how my BlueLab Truncheon EC probe works and hooked it up to the oscilloscope with a number of different salt solutions to look at the waveforms it produces. After that I took a look online into why EC probes must use an AC current when measuring, and then for good measure I built up the circuit I found using Google and calibrated it against three different salt solutions. Finally, a quick look at some of the other probes and widgets I've bought myself to go with my hydroponics setup.
Here's a link to the page I found using google which contained the molecular simulations, circuit details and instructions which I followed in this video. www.octiva.net/projects/ppm/
Here's a good article on Single-Slope Integrating ADCs - This is what I belive that the BlueLab Truncheon is doing. www.maximintegrated.com/en/app...

[@RandyFPV]

Hi. I am the original designer of the dissolved solution meter made by NAGS. When I made our probe we used 316 grade stainless steel, it does not corrode and it stays clean for months. You can by it in welding supply places, it was basically welding rod we cut into tiny pieces. The only problem is that it is impossible to solder to, so I made a tiny circuit board with 2 slots that the rod was forced into to make and mechanical and electrical connection, there was also a thermistor on there to allow for temperature compensation. Then the whole thing was coated in epoxy to keep it water proof.

[@RWBHere]

Thanks for the information, Randy.

[@ruftime]

Thank you Jim! I'm an avid hydro gardener and just started learning electronics and playing with micro-controllers. Very techinical of course, but delivered in a manner that I'm not feeling too overwhelmed:)

[@ThingsWhichArentWork]

Thanks +Canyon Racer - I'm a great believer that the difference between easy and difficult is how well explained it all is. I find a lot of explanations confuse the hell out of me, but if I read enough of them eventually I'm able to work out a simple enough way of understaning what's going on. Cheers!!

[@andrewr900]

This was an awesome video! Although I did not need to learn exactly how these work, I find it fascinating and I’m sure in the future, this will become very useful!

[@monty671]

Jim, You brought back old times. I have not used a scope for almost 15 years. Almost miss it. In my younger years I worked radio and radar, and anything else the boss figured I could fix. You explained the subject well without adding obscure formulas that would loss many. Thanks.

[@ThingsWhichArentWork]

Ronald Montgomery Heh... and on the flip side, I've been hankering after a scope for about 15 years so that I could try some more involved repairs (the ones which I can't tackle just a multimeter). Glad you found my explanation understandable - I was never good with all those complicated formulas myself. Thanks for watching and taking the time to comment. Cheers!!

[@5Komma5]

Very interesting video. I am about to connect my EC and pH measurements to Home Assistant. Your video helped a lot. Thanks!

[@microk7648]

Jim, that is a really really good video. Funny and informative. Keep up the good work!

[@zanethackeray7607]

Fantastic. Thank you. Looking forward to the pH vid.

[@francescadaszak]

I realize that this video is very old now, but I just wanted to thank you for the effort put into this video!! It was incredibly helpful! Also, at 6:40 when you say that nobody is actually wondering, I was actually wondering that EXACT thing!!! Thanks :-)

[@ThingsWhichArentWork]

Thank you Francesca - It's always nice to know that this video came in useful for someone. Cheers!!

[@copernicofelinis]

​@@ThingsWhichArentWorktwo years later, it is my turn to thank you for making this public.

[@GaryMcKinnonUFO]

This was insightful, thank you. I bought one of those cheap EC modules that you use with arduinos and the like, it works very well until it's in the same container as the pH probe, which it increases the reading of. So it seems to be AC interference. I tried shielding both with aquarium air tubing and aluminium foil but no joy. I did read that some commercial units just amplify the pH probe in comparison with the EC probe. I powered them both separately with batteries in case it was a ground-loop problem but no joy.

[@Neighbour_Al]

Nice! I want to install some sensor probes in my orchard to measure soil moisture and the like (relative changes), and this looks like the solution. I got an Arduino for Christmas, so it might get put to the task too. Many thanks for sharing. Finding the right transmit amplitude and probe gaps is going to be the challenge.

[@SimonFiliatrault]

amazing work Jim exactly what I was looking for thanks

[@ThingsWhichArentWork]

Thanks Simon - Glad you found the video useful. Cheers!!

[@SleestaksRule]

This is really cool. My Bluelab stopped working after 5 years or so. I still have it. Time to figure it out.

[@ThingsWhichArentWork]

Thanks Ted - I'd sure like to see the insides of the Bluelab if you get around to taking it apart - I was tempted to dismantle my one, but couldn't find any way of getting it to pieces - I think the sticky label needs to come off, and I didn't fancy my chances of getting it off and back on in one piece. Cheers!!

[@gabucarneiro]

Fantastic! Amazing explanation, fun and real deal! Subscribed

[@ThingsWhichArentWork]

I decided to take a look at what my EC probe was doing, and ended up building the circuits to run a generic ebay cheap probe. All electronics this time and rather technical throughout, but hopefully some of you will be able to understand what I'm waffling on about. Cheers!!

[@ignaciolopezgodoy8079]

Hi, Im working on it. Would u mind giving me a link or some thing where the needed components for the EC metter are listed. Im reading values with my Arduino but it´s not working right. Thanks!

[@srikeshiyer2695]

What is the brand of the EC probe that you used? Can this probe be immersed in solution for continuous monitoring?

[@101blog]

Good one Jim didn't even need to be told about it this time! Good explanation on conductivity A/C vs D/C etc also I was glad that the commercial and your probe agreed so well! Waiting for your next installment

[@ThingsWhichArentWork]

Cheers John - I've already been soldering up a more robust prototype on stripboard this evening - Typically, it is not working at the moment :) Cheers!!

[@101blog]

Jim Conner Yeah normally I wouldn't of risked videoing the Breadboard but it worked well this time and always look rather mad scientist

[@ThingsWhichArentWork]

101blog I'll be honest, I'd already made up the oscillator part of the circuit before I began filming the video at all. I was so pleased when I got a nice clean sine wave out of it that I wanted to share the construction process, so I did the bluelab analysis to see if it was working the same way as Isabella's circuit (which it wasn't). Cheers!!

[@aquamechanicspro1638]

Im impressed ! Great job ! Thanks a lot !

[@tnos121]

Hi Jim. what a great video. awesome loved it. Best info and tutorial i have seen. well done mate. Thanks

[@ThingsWhichArentWork]

Thanks Tony Nos - Very glad you liked it. Cheers!!

[@amirhosseinmohammadpour4555]

Amazing video, thanks a lot.

[@sukhithalakwan]

Wow mate ,literary a ton of knowledge 😳 👏

[@stdavross666]

great video, thanks

[@simonparker4992]

Thanks. Very good.

[@bhavinpithawala3967]

very useful and fun...

[@TraceWaters]

Good stuff!

[@ThingsWhichArentWork]

Thanks Trace. Glad you enjoyed it. Cheers!!

[@GaryMcKinnonUFO]

Isabella's website looks like a great source, i wonder if i could use chopped DC to avoid AC interference?

[@RahulKumar-zs2wv]

thanks Jim yes I am getting higher voltage value in tap water and lower when dipped in salt water . I don't kw y

[@MyANDHIE]

nice video..!!

[@ajayjoseph4626]

Thanks for the video Jim. I am not sure what unit this BlueLab instrument is measuring EC. I thought it should give output readings in Siemens or Ohms. I want to measure a solution in 500uOhms. Do you think this design will be able to do it? I will rig it up on an arduino and I will be happy to share the code. Cheers anyway Jim

[@chakreshjoshi4302]

nice

[@muhammadsyafiq7760]

Currently making this exact EC. Can you help me with my problems. Stuck and cannot finish it.

[@RahulKumar-zs2wv]

hi.. jim thanks for your video. in video i have seen that output wave form across oscillator is AC , and you are getting 17 v p-p bt supply to op-amp is +12 n -12 how i is possible ? and can u tell me that what is AC v across pin 7. and how to get -12v supply?

[@ThingsWhichArentWork]

Hi +Rahul Kumar. The + and - 12v rails give us a total of 24v peak-to-peak that we could move through, so 17v p-p isn't any special kind of magic. When I made this video I was using my triple-output bench power supply to give the + and - rails, but since then I've purchased a dedicated DC/DC converter to solder onto the board... I'm using this one cpc.farnell.com/1/1/192485-powerpax-1pe1212s-wr2-dc-converter-1w-12v-12v-dual-op.html .. Hope that helps. Cheers!!

[@RahulKumar-zs2wv]

thanks jim . at the output pin 14 of op-amp i am getting in mV. after dipping in salt water also output is in mV range. what to do. is i have to multiply that values with 500 as given in sheet .

[@ThingsWhichArentWork]

Hi +Rahul Kumar - You should be getting a higher reading than that in salt water. If you were getting 1V output that would indicate that your EC was 500. Do you have an oscilloscope so that you can probe various parts of the circuit? It's probably worth taking a look at pin 8 before it feeds into the bridge-rectifier.. You should have a reasonable voltage at that stage (enough that loosing 0.7v across the diodes isn't an issue), so should be easy to probe... Probably also worth checing your power supply rails (always check voltages first). You might be able to find some more debugging help from the original webpage where I found the circuit diagram.. www.octiva.net/projects/ppm/ ... Hope that helps. I don't know what else to suggest. Cheers!!

[@diablo4652]

hi jim: i am trying to make a similar sensor with salinity range from fresh to solubility (for NaCl which is about 225 part per thousand) or 200 ds/m, have you tried to work on that large range? thanks

[@ThingsWhichArentWork]

Hi Chenming - The maximum I need to measure for my nutrients is about 2500ppm, but there's no reason that this same circuit shouldn't be able to measure much higher ranges. EC is just a measure of the liquid's electrical conductivity.. The high-frequncy AC measurement is used to stop electro-chemical reactions from occuring, at the electrodes, so most of this circuit is just dedicated to either generating the AC frequency, or filtering it back out again so that you can get a good DC reading value... If you turned down the sensitivity of the amplifier parts of the circuit, then you should be able to measure any strength that you like. Hope that helps. Cheers!!

[@skhumbuzocele1330]

I have very little information on electronics. With the little knowledge I have I do NOT thing you need a lot of Operational Amplifiers to make an EC meter, You need only one to oscilliate the circuit and the change in voltage can also be read by most volt meters as AC, no need for conversion to DC to read the voltage reading.

[@rollerben88]

I was just asking in my head "why can't you just use a multimeter?".... That was a very good find with that website there as well :)

[@ThingsWhichArentWork]

I would be useless without Google - Thank goodness for all these other nice kind people who do all the hard work for me :) Cheers!!

[@rollerben88]

No no that's not what I meant Jim! Just saying that for such a nichè item there is a whole Web page set up on exactly how to make one

[@ThingsWhichArentWork]

Ben Hill Sorry - I think we misunderstood each other's misunderstandings :) - It's been a long-running belief of mine (over a decade now) that all I ever do is google stuff & cut 'n' paste the results. My ninja google-fu is my secret special ability for both work and play. I was wearing that particular CTRL-C+CTRL-V T-Shirt because I was all too aware that the video was essentially a 'look at this web page I found' experience, but it was a damn cool webpage and as I was enjoying building up the EC probe circuit I thought I'd share what I was up to with everyone else. Thanks again for taking the time to comment. Cheers!!

[@fernandoescamilla3662]

Hi Jim, im about to start doing this project following your steps, but I havent decided which probe to use. I am trying to find low cost probes, can u recommend me any?

[@ThingsWhichArentWork]

Hi +Fernando Escamilla - If I did this project again, I think I'd have a go at making my own probe too... The commercial/industrial probes are expensive because they use platinum for the contacts (because platinum doesn't react with the water in any electro-chemical way), but apart from the platinum, it's just a plastic tube with a co-ax wire coming out the back - there's no electronics inside them at all. Platinum is expensive stuff (£6/cm for platinum wire on ebay in the UK)... If you're just checking nutrients periodically though, you can most likely get away a different metal for your probes... Stainless steel does well in high-salt marine environments, so will survive quite well with nutrients. Technically speaking stainless will react with the solution when a current passes through it... stainless contains chromium which will very very slowly react, but given the miniscule currents involved, and the fact it's a high-frequency AC waveform we're driving the probe with, the reaction will be pretty close to nothing... So... two stainless stell bolts, and plastic tube and some co-ax and you're good to go.... If you have problems with that setup you can always swap to a platinum probe in the future. Hope that helps. Cheers!!

[@misterhide1979]

Hi Jim! Beautiful video! i have one question for you: Which type of EC probe do you use in this video? Thank's a lot! Best regards!

[@ThingsWhichArentWork]

Hi Dave - It's a Bluelab Truncheon. Practically indestructible, batteries last for a few years at a time and it's great for stirring the nutes around in the water tanks. Cheers!!

[@StefanRogin]

7 years later I'm wondering what you thought I'd wonder.

[@petrusraats65]

One can also send dc current one way, take a reading, send current opposite way, take a reading and average the two readings. Almost the same as a/c!!!

[@chakreshjoshi4302]

:thumbs_up

[@meehan302]

Always interesting Jim. I have more googeling to do.

[@ThingsWhichArentWork]

Thanks Patrick. I've been doing lots of googling myself this week... all about pH probes (which might make it into a video this weekend). Thanks for watching and taking the time to comment. Cheers!!

[@OrbiterElectronics]

I did actually wonder why the voltage went negative Jim. Mind due i wouldn't have had a clue as to what was inside one of those things so that wouldn't help :-) Oh, and I say why measure with a meter when you've got a nice scope :-) hehe. Cheers mate John

[@OrbiterElectronics]

Ps... Love the JimCad ;-)

[@ThingsWhichArentWork]

Thanks John - As you've probably guessed already, I'm loving that scope. The only problem is that I now have to tackle some electronics repair jobs which have been on hold for years waiting for me to get that scope. Cheers!!

[@electrodacus]

Good video. Now you just need to automate everything add some cameras connected to web sell to people a plant that they can care for as they want in an interactive way :)

[@ThingsWhichArentWork]

Thanks Dacian...... Now there's an idea.... Like one of those virtual pets for your desktop, but with a real plant... Cheers!!

[@joshidj2000]

Hi, is it possible to use battery and +-3.3V to power this circuit, instead of+-12V?

[@ThingsWhichArentWork]

Hi Dharmesh - That's not possible with this particular circuit as the op-amps used won't work at that low a voltage. It would however be possible to use some small boost converters to generate the +-12V supply from a lower voltage. I was planning to use a PowerPax 1PE1212S converter for the role myself, but that one is designed to boost up from 5V to +-12V rather than the 3.3v supply you have... I expect someone makes a similar converter which works from 3.3 volts though. Hope that helps. Cheers!!

[@joshidj2000]

My battery will be 4.2V, what would the lowest voltage possible? From the datasheet of TL074 it shows +- 5V, but what effect would that have on the circuit or reading? If so i then can use a simple inductor less step-up dc-dc

[@ArthurDenzlin]

hi Jim the website u mention has been taken down! do u happen to have the circuit with you? thanks.

[@ThingsWhichArentWork]

Hi +Arthur Denzlin - Just search for 'EC Probe Schematic' using Google Image search - You're after the one which says 'EC/PPM/TDS Meter' at the top of the page... It looks dark-grey because the image has a load of little grey dots on it... but you can clean them up using a contrast/brightness filter in the image editor of your choice. Hope that helps. Cheers!!

[@ArthurDenzlin]

+Jim Conner thanks jim i found the circuit!

[@rozaidirais9601]

Hi..can your EC probes be connected to Arduino (Microcontroller)?

[@ThingsWhichArentWork]

Hi Rozaidi Rais - Yes - the circuit I built in this video was to get the voltage levels from the probe to something compatible with a microcontroller - Should work great with an arduino (or any other microcontroller)

[@RahulKumar-zs2wv]

hi jim in your video at 14 min you are showing voltage value increases as concentration of salt increases. but with me it happening reverse .it showing nice increment at 8 pin bt at 14 pin decrement.

[@ThingsWhichArentWork]

Hi +Rahul Kumar - I haven't forgotten about you... I've dusted off the circuit I made and will try to get it plugged in to check voltages this evening after my kids are tucked up in bed. Sorry for the delay. Cheers!!

[@ThingsWhichArentWork]

Hi +Rahul Kumar - Pin 8 should be giving you an amplified version of the sine wave coming through the EC probe. It'll should be AC rather than DC at that stage... after that it passes through the bridge recitifer to turn it into DC... gets smoothed by the RC filter made from C3 and R8 and then passes into the last op-amp stage for level shifting and amplification. I've just tested with a random-strenght salt solution (somewhere around EC 3.5)... I'm getting 1.1VAC on pin 8, which is giving me 7V out on pin 14. Hope that helps. Cheers!!

[@RahulKumar-zs2wv]

+Jim Conner in tap water at 8 i am 700 mV ,at 14 300 mV . in salt water at 8 its 900mv , at 14 200mV ? is it correct?

[@ThingsWhichArentWork]

Hi +Rahul Kumar - It sounds as your last op-amp is not amplifying things correctly... The numbers at pin 8 aren't too unreasonable, but you might want to tweak the variable resistor V2 to push the values a bit higher. There's a 0.7v voltage drop across the bridge rectifier, so not much of the signal from your 700mv and 900mv measurements on pin 8 will be arriving at the final op-amp stage. Hope that helps. Cheers!!

[@bedlore]

Brilliant. I hope your "Mixologist" will be generic enough for us aquaponicers to utilise too :) Will you base it on something like a Rpi?

[@ThingsWhichArentWork]

Thanks Brendan. I will try to make The Mixologist as generic as I can - I've been playing around with a Freescale FRDM-KL25Z this week - it's pin compatible with Arduino shields, but has a much more powerful CPU. I am currently worrying that my ambition with this project may exceed my abilities. Cheers!!

[@lkhbhydroponic6858]

Hi mine is just stop working suddenly. Does anyone know how to fix it?

[@ThingsWhichArentWork]

Stopped working totally, or giving wildly wrong readings? ... I found that using the BlueLab truncheon for stirring calcuim nitrate solution causes a greasy buildup on the tips of the probe and prevents it from making contact with the liquid correctly. Bluelab supply a cream-cleaner specifically for cleaning the probe tips which seems to help for a while, but has not permanently fixed my own bluelab truncheon... just seems to make it work for a few hours each time I use it. If it's totally dead, I'd look to the batteries and their connections... Hope that helps. Cheers!!

[@lkhbhydroponic6858]

Jim Conner well it was wildly irradic for while and then stop working completely. I checked the batteries and changed the battery but no success don't know what to do. I can't get the blue lab cleaning solution . Is there any other way to clean it.?

[@ThingsWhichArentWork]

Kitchen cream cleaner I think should be OK. The probe tips are pretty robust and designed not to be damaged by ph-up/ph-down solutions etc. Just make sure it's all thoroughly rinsed off afterwards so that the cleaner doesn't sit there eating away at the contacts after you've finished cleaning. (Please note... 'I think should be OK'... I don't work for bluelab and am just guessing based upon what their bluelab branded cleaning product smells like - If you ruin your probe, please don't blame me). Cheers!!

[@lkhbhydroponic6858]

Jim Conner thank you . I'll certainly not going to blame you. I'll try it and I'll let you know what happens .

[@lkhbhydroponic6858]

Yup it worked. Thank you

[@sshutupurface8345]

both those links don't work

[@leftystrat62]

I hung in there as long as I could (6:50) but I think I came into the wrong room if you know what I mean :)

[@ThingsWhichArentWork]

Heh - I know exactly what you mean, but you stopped just one second before it got really interesting :) .... or perhaps not... This one was rather long winded and technical, but I was on a mission to find out how they worked.. down to the very last detail. The pH probe one I did following this was equally long winded and technical too - it all seemed so interesting when I was investigating it all... but seems rather dull when I watch it again now. Have a great weekend. Cheers!!