Re: [DIYbio] Conductivity measurements with Bipolar Pulse

Hi Nathan,

Thanks for the tip about the dual supply.

But for now, I'm using the Arduino digital pins to generate the
alternating pulses.

The circuit set up is this:
http://www.c2o.pro.br/hackaguas/figuras/condutivimetro_00_bb.png

Where Rx is the solution resistance.

And the pulses are generated switching the levels (high and low) of pin
7 and 8 of Arduino:
http://www.c2o.pro.br/hackaguas/figuras/condutividade_efeito_frequencia_01.png

I'm imagining that for the solution is important only the difference of
voltage between the two electrodes.

If in the first pulse pin 8 is 5V and pin 7 is at 0V and in the next
pulse pin 8 = 0V (LOW) and pin 7 is 5V (HIGH) so I'm reversing the
polarity. Right?

I imagine that would be the same as using a symmetrical dual supply and
apply at pin 8= +2.5V and pin 7= -2,5V and then pin 8= -2,5V and pin 7=
+ 2.5V. Right?

In both cases I apply at the electrodes a difference voltage of 5V and
alternating. Do you agree?

Some info about the Bipolar Pulse: https://goo.gl/qBd6CO

My intention in Bipolar Pulse is to evaluate whether it would help to
increase the range of linear reading for samples with different
conductivities without changing the electrode.

And I have also a great interest to study more about analytical
techniques based on voltammetry and use Arduino to make DIY systems for
quantitative electrochemical analysis in water. Do you suggest any
mailing list (or forum) where I can meet other people with similar
interests?

Thank you very much for your comments.

Best Regards,
Markos

On 17-11-2015 17:09, Nathan McCorkle wrote:
> It sounds like you need a dual-voltage power supply. There really
> isn't such a thing as "negative" voltage... for example if you have a
> 9V power supply, you could say that 4.5V is a "virtual ground", and
> then 0V would appear as "negative" relative to your "virtual ground",
> and the 9V wire would appear like 4.5V relative to "virtual ground"
> (again, which is actually 4.5V relative to 0V wire).
>
> A simple circuit is shown here, though you can get more complex ICs
> that are more efficient, this has few parts and is simple:
> http://electronics.stackexchange.com/a/79317/34413
>
> So with something like that in place, you connect your arduino GND pin
> to the "virtual ground" and the PWR pin to the "virtual 4.5V"
> (assuming you have a 5V tolerant Arduino). Then using transistors, you
> can pulse your analysis cell with your "positive" and "negative"
> polarity pulses.
>
>
> Stripping voltammetry is another interesting and related technique,
> where you hold a voltage for some time, then slowly alter the voltage
> and watch the current response... basically you plate ions to the
> electrode, and then slowly drive them off. There are characteristic
> current curves, since different ions electrolyse at different
> voltages, so you can determine minute amounts of metals and their
> concentrations (if you have standards to calibrate against). There are
> also interesting impedance spectrometry techniques... where you
> generate an electrical wave, watch the current flowing, then do this
> while changing/scanning through a range of frequencies. Lots of neat
> stuff! It's all electron interactions at some point! So might as well
> learn to use them!
>
>
> On Tue, Nov 17, 2015 at 4:50 AM, Markos<markos@c2o.pro.br> wrote:
>
>> Hi,
>>
>> I'm trying to implement a conductivity meter with the Arduino board. My
>> intention is to keep the electronic circuit as simple as possible.
>>
>> I'm only using a voltage divider as shown:
>> http://www.c2o.pro.br/hackaguas/figuras/condutivimetro_00_bb.png
>>
>> The alternating pulses are generated by switching the signals from pins 7
>> and 8 of Arduino:
>> http://www.c2o.pro.br/hackaguas/figuras/condutividade_efeito_frequencia_01.png
>>
>> For now I'm using two steel wires as electrodes:
>> http://www.c2o.pro.br/hackaguas/figuras/eletrodos_00.png
>>
>> My intention is to be able to control via software some measuring
>> parameters, such as electrode polarization time. And adjust these parameters
>> on the fly depending on the sample concentration range.
>>
>> Recently I started to read some papers about bipolar pulse technique:
>> http://pubs.acs.org/doi/abs/10.1021/ac60285a015
>>
>> The bipolar pulse technique for measuring solution resistance minimizes the
>> effects of both the series and parallel cell capacitances. The technique
>> consists of applying two consecutive voltage pulses of equal magnitude and
>> pulse width but of oposite polarity to a cell and measuring the cell current
>> precisely at the end of the second pulse. (Source: Peter Kissinger, William
>> R. Heineman, Laboratory techniques in electroanalytical chemistry)
>>
>> Does anyone has any experience with this conductivity measuring technique?
>>
>> Thanks for any tip,
>> Markos
>>
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