Recreating EC circuit

cyrusthevirus · Mar 19, 2010

I am trying recreate a circuit I found online. The circuit is used to measure the electrical connectivity in a liquid. The circuit below also requires a probe and volt meter/pic to read the output. I have created a list of parts and just want to make sure I got them correct. The post I found online was from back in 2006 and my attempts to reach the person who created have been unsuccessful.

In addition to the parts below, What is D3? I believe it is a bridge rectifier. Can anyone suggest a part number or specs I should look for?

Finally from what I can tell the circuit appears to be fed by +12VDC and -12VDC. I plan to get this from a +12VDC circuit and a NJU7662 power inverter.

The specs are here:

https://media.digikey.com/pdf/Data%20Sheets/NJR%20PDFs/NJU7662.pdf

Here are the parts:

R1 1K (1/4W)
R2 1K (1/4W)
R3 56K (1/4W)
R4 33K (1/4W)
R5 100K (1/4W)
R6 1K (1/4W)
R7 6.8K (1/4W)
R8 22K (1/4W)
R9 1K (1/4W)
R10 220K (1/4W)
R11 220K (1/4W)
R12 220K (1/4W)
R13 100K (1/4W)
R14 100K (1/4W)
R15 82K (1/4W)

U1 TL074
V1 100K (trimmer resistor) (1/4W)
V2 2K (trimmer resistor) (1/4W)
V3 22K (trimmer resistor) (1/4W)

C1 .015uF (ceramic)
C2 .015uF (ceramic)
C3 .22uF (ceramic)

D1 In4733A
D2 In4733A

R200 3.9K (1/4W)
C200 10uF (ceramin)
D200 In4150
D201 IN4150

cyrusthevirus · Mar 21, 2010

Anyone? Here is a link to the original circuit discussion.

EC/TDS/PPM Meter

Hero999 · Mar 21, 2010

Yuck, I had to play around with that circuit in the Gimp to make it readable. I don't know why they didn't use a plain background, surely the CAD program has an option to turn the grid off.

Yes, D3 is just a bridge rectifier.

The power inverter IC might not be powerfull enough.

Are you powering this from a 12V mains power adaptor?

If so you could use an AC adaptor and a voltage doubler circuit to get +/- 12V.

ericgibbs · Mar 21, 2010

cyrusthevirus said:
Anyone? Here is a link to the original circuit discussion.

EC/TDS/PPM Meter

hi,
The D3 is a bridge, I would say, make up a full wave bridge for this project using 4 off, 1N914 or 1N4148 signal diodes.

As you say its powered by +/-12v

JimB · Mar 21, 2010

A note of caution!

On the very dotty circuit attached by cyrusthevirus, and the tidy version posted by Hero, there is a connection missing from pin9 of U1 to the bridge.
On the circuit in the original article, that connection is there.

There may be other oddities in the circuit as copied by cyrus, I did not notice any others, it is just that this one screamed out at me!

JimB

Hero999 · Mar 21, 2010

JimB said:
A note of caution!

On the very dotty circuit attached by cyrusthevirus, and the tidy version posted by Hero, there is a connection missing from pin9 of U1 to the bridge.
On the circuit in the original article, that connection is there.

Sorry, I can't see it.

On both circuits pin 9 is connected to the bridge.

JimB · Mar 21, 2010

Weird stuff going on here!

I had a look at the diagrams in this thread using another computer, perfect.

Looked again with this one, line missing.

Downloaded the file from its original site to this computer and displayed it using Windows Picture and FAX Viewer - perfect.

Look at the picture again in this thread - prefect. WHAT!!!!

Reboot this computer, look at the picture in the thread, line missing.

There seems to be something a bit odd about the video driver in this computer that is sorted by running Windows Picture and FAX Viewer.

As I said - WEIRD!

JimB

cyrusthevirus · Mar 21, 2010

Hero999 said:
Are you powering this from a 12V mains power adaptor?

That was my plan.

Hero999 said:
If so you could use an AC adaptor and a voltage doubler circuit to get +/- 12V.

Can you expalin this further?

cyrusthevirus · Mar 21, 2010

ericgibbs said:
The D3 is a bridge, I would say, make up a full wave bridge for this project using 4 off, 1N914 or 1N4148 signal diodes.

Great this is what I was looking for.

Hero999 · Mar 22, 2010

You need an AC adaptor (i.e. 12VAC, not 12VDC) in order for this to work.

It's only suitable for low currents, up to 50mA or so but that's enough for your circuit.

You might not need the regulators so you can omit them if they're not required. You can also save space by using the LM78L12 and 79L12 which are in TO-92 packages. Note that the pinout for the negative regulator is different to the positive, see the datasheets for more information.

cyrusthevirus · Mar 22, 2010

Excellent. I did a quick search on the parts you suggested and came across a PCB listed here:

http://www.musicfromouterspace.com/analogsynth/WALLWARTSUPPLY/WALLWARTSUPPLY.php

Looks like it will do the trick, thanks for all of your help.

One last question, the circuit lists "VACout" Just below R9. Any idea why?

Hero999 · Mar 22, 2010

What do you mean? There is no R9.

The input is AC and the output is bipolar (both positive and negative) DC.

cyrusthevirus · Mar 22, 2010

Sorry, I did not clarify. On the original circuit, VACout is listed.

cyrusthevirus · Mar 25, 2010

Any thoughts on why the VACout is listed in the original circuit?

Hero999 · Mar 25, 2010

I couldn't see a VAC out anywhere - point it out to me.

cyrusthevirus · Mar 25, 2010

I highlighted in the attached pic.

audioguru · Mar 25, 2010

It is obvious that the VACout signal is the attenuated sine-wave from the oscillator amplified by U1b.
The resistance between the probes controls the gain of U1b.

cyrusthevirus · Mar 25, 2010

Okay so it just for testing, Right?. I wanted to make sure that it did not need to be connected to something.

audioguru · Mar 25, 2010

VACout is already connected in the circuit. It is for you to see what is going on.

cyrusthevirus · Mar 26, 2010

Great. Thanks for everyone's help.

Recreating EC circuit

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