DIY Conductivity Probe/Meter

I have most of the parts in my bin but they are SMT. I have the through hole caps, diodes and resistors but not the opamp. I guess I will toss the stuff I need in the cart and order it along with the transducer. Not sure if I need the board yet. I may just do it on the breadboard first. I will order mult-turn cermets for the trimmers and metalized poly MKTs for the two RC caps. Looks like the brdige cap should be aluminum electro to smooth the ripple and the 1n4148 diodes can be just about anything. I wonder of a precision bridge would help?

I have ordered TDS probes from HM digital so don't need the BNC either.

Let me know how things progress.
 
The more I look at that schematic, the more I see room for improvement.

1) I have not taken the time to breadboard the circuit but am not convinced that the Wien Bridge is going to be stable or oscillate at the proper frequency, the component values just don't appear correct. There is no gain control, meaning that the sinewave will be distorted or clipped and the stability will drift with impedence and temperature.

2) I think there should be a buffer stage after the oscillator.

3) An Opamp would likely work much better as an attenuator (instead of the two diodes).

4) I don't see a need for the bridge rectifier. It looks like he is using it in conjunction with an opamp precision rectifier... It does not appear to make sense.

I have a more stable and conventional circuit in the simulator right now. The wien bridge will be equiped with gain control so that it will be self stable. You shouldnt need a scope to set the oscillator then. I have also ordered a sinewave generation chip and will play with that as well.
 
cyrusthevirus said:
How long until you can do further testing?
Click to expand...

Killed the last 7905 regulator a while back... just ordered a pile from ebay and will order the prototype parts for my design tomorrow. I also ordered a new bench supply today (Cheap Mastech) because I lost a auction (fell asleep at the wheel) on a really nice triple output Lambda bench PSU.
 
I have not even had a chance to work on it. I am still working to complete the lighting system. I currently only have a sump running which is filled with live rock. So my priority is the lighting system so I can setup the main tank. We do however have another person who will begin testing with us soon. I should be sending out a board and probe to him this week.
 
Great!

Don't get me wrong... I have a feeling the circuit will work, I just think it will be tempermental and can be improved upon :) I did not intend on designing my own and had hoped that somebody else already did the work. We all know how that goes though.
 
I did not build that circuit (for the reasons I mentioned). I have designed my own and have all of the parts on the bench, but have not had a chance to toss them on the breadboard yet. I have my hands full with a new custom shed (workshop for wood and electronics) and our clubs summer picnic (I am hosting) along with work.
 
DIY Conductivity Probe/Meter Reply to Thread

DIY Conductivity Probe/Meter Reply to Thread

Hi

Just wondering if anyone is pursuing this project.

I am really keen to build a diy salinity sensor,

I too tried this one http://www.octiva.net/projects/ppm/ but then found it only goes up to something like 2500PPM salinity. So when I tried it out on salty water the circuit was way off the scale.

Obviously for testing fresh water.

drinking water - 100 ppm
restriction on drinking water - 500 ppm
limit drinking water - 1000 ppm
limit agriculture irrigation - 2000 ppm
brackish water - 500 - 30,000 ppm
sea water - 30,000 - 50,000 ppm
brine > 50.000 ppm

I would love to hear if anyone is still working on this, and have any more nuggets of information.

Does it get harder to get a conductivity measurement when salt levels get above 2500ppm ?

Cheers

Simon
 
Not sure, but I thought it was the probe that set the level, not the circuit.

BTW I sent you an email about the cost for a test board.
 
You said in your other post that you were not trying to sell anything, yet your site does not have schematics or firmware and appears to be a sales pitch with "hobbyists and developers" as your target.

Your name "OEMTDS" appears to directly indicate that you are a product manufacturer.

You appear to be asking questions in order to understand what our hobby needs in the way of sensors. Will you be providing schmatics, circuit operation explanation and open source firmware? Your other post does indicate "open source" so where is the source?
 
It is an open source when someone emails me or shows interest SIR...so far i got nothing but bunch of bickering from you . Yes i kept my nickname oemtds which means nothing but a tds.Besides does that web link look like a business page to you? I see lots of ppl promoting their tanks and set ups as being one of a kind ,why cant I ?
 
simon owl said:
Hi

Just wondering if anyone is pursuing this project.

I am really keen to build a diy salinity sensor,

I too tried this one http://www.octiva.net/projects/ppm/ but then found it only goes up to something like 2500PPM salinity. So when I tried it out on salty water the circuit was way off the scale.

Obviously for testing fresh water.

drinking water - 100 ppm
restriction on drinking water - 500 ppm
limit drinking water - 1000 ppm
limit agriculture irrigation - 2000 ppm
brackish water - 500 - 30,000 ppm
sea water - 30,000 - 50,000 ppm
brine > 50.000 ppm

I would love to hear if anyone is still working on this, and have any more nuggets of information.

Does it get harder to get a conductivity measurement when salt levels get above 2500ppm ?

Cheers

Simon
Click to expand...


That design is not an ideal salinity tester . I do have much better schematics but what do i know im just promoting a product here huh.
 
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