Potentiostat Circuit

Using Arduino Project Guidance
1

Hello, I built an Arduino-based potentiostat following this paper. To troubleshoot the potentiostat, I connected the RE,WE, and CE to a 10KOhm resistor. The expected graph should show a linear relationship, but I'm getting those results. Could this issue be due to using two 9V batteries without connecting them to a potentiometer?

452588511_2447580748965259_3058855969517491722_n
452588511_2447580748965259_3058855969517491722_n1416Ă—1115 315 KB

2

Please post schematics. Pictures of spagetti are useless.

1 Like
3

The schematic can be found in the paper.

4

What results??

1 Like
5

Many of us helpers has the rule to not download unknown things. It should be posted here. It's Your choice if You want help or not.

2 Likes
6

Connect the CE to RE. Then connect a 10K resistor between WE and CE
Also try a 1K resistor

7

Sorry about that. Here is the schematic as well as the code. Please let me know if you require any additional information.

#include <LiquidCrystal.h>
LiquidCrystal lcd(8, 9, 4, 5, 6, 7);
int a = 10;
int val = 0;
float ct = A0; // ADC
float c = 0;
int n = 0;
float Potstep = 0.0078; // fixed due to the DAC resolution
int vevals[] = {100, 20, 50, 100, 200, 250, 300}; // multiple scan rates values (mV/s)
int const count = 6;
long intervalos[count];

void setup() 
{
  TCCR1B = TCCR1B & B11111000 | B00000001; // Set dividers to change PWM frequency
  Serial.begin(9600);
  pinMode(a, OUTPUT);
  pinMode(ct, INPUT);
}

void loop() {
  for (int pos = 0; pos < count; pos++) {
    intervalos[pos] = (1000000L / ((vevals[pos]) * 128L));
  }
  for (int pos = 0; pos < count; pos++) {
    n = 0;
    while (n <= 1) {
      // Start the forward scan
      for (val = 0; val <= 255; val++) {
        analogWrite(a, val);
        delay(intervalos[pos]);
        c = analogRead(ct);
        Serial.print(val);
        Serial.print(",");
        Serial.print(c);
        Serial.println();
      }
      // Start the reverse scan
      for (val = 255; val >= 0; val--) {
        analogWrite(a, val);
        delay(intervalos[pos]);
        c = analogRead(ct);
        Serial.print(val);
        Serial.print(",");
        Serial.print(c);
        Serial.println();
      }
      n = n + 1;
    }
  }
  // Stop the loop after one full cycle
  while (true) {
    // Infinite loop to stop further execution
  }
}

schematic
schematic1002Ă—660 30.6 KB

8

graph
graph1000Ă—600 78.6 KB

These are the Digital to Analog converter (DAC) and Analog to Digital Converter (ADC) values that I am getting.

9

Oh okay thanks I'll try that out.

10

Do you have the original paper that explained that design

acs.jchemed.5b00961.pdf (1.0 MB)

1 Like
11

Thanks!
I would like to change the circuitry before A0. 5.1 volt zener and then an LED adding its forward voltage gets a bit too high. A 4.7, or 4.3 Volt zener would feel better. If this cures the issue, I can't tell.

12

Yeah here is the link to the paper.

13

It seems working.
Reduced a little bit the span of the d/a pwm ( as I'm using reduced power supply ), not to saturate the output.
I think the WE and CE terminals are reversed ( according to fig 5 of this document )
Doing this the 'resitor test' works ok ( I mean shorting RE and CE and connecting a resitor between the short and WE )

potentiostat01
potentiostat01869Ă—745 20.8 KB

This is the schematic I used, not different from the original, only using lower supply voltage

potentiostat00
potentiostat001570Ă—1074 11.5 KB

14

No the one I show in post #10

15

Check your battery polarity, I think you may have them backwards.
Also remove the LED. Never use an LED without a current limiting resistor.
image

image

16

Thank you so much this fixed the problem. I am getting a linear relation now.

Figure_1
Figure_11000Ă—600 21.5 KB

17

The problem I'm having now is the battery is being drained very fast. I connected 2 new 9 volts batteries today and only ran test for about an hour but the voltage of both batteries dropped to 8V. Should I use a variable resister in my circuit to prevent the batteries from draining?

18

Don’t use a resistor. It will only cause problems. Depending on the quality of the batteries you are using this may be normal. Are they Alkaline or are they carbon/zinc “heavy duty” batteries?

Batteries are not “dead” until discharged to 1,1 volts/cell which is 6.6 volts in your case.

19

I'm measuring current consumption is 1.2mA at 6Vcc, which is in accordance with the datasheet which says 1mA max at 5V.
The original circuit had lower resistances on the summing amplifier ( only to waste several mA ). A 'normal 9V battery' should have a capacity of 400mAh ( or more ) so it should last 40h ( considering a worst case of 10mA current consumption )

20

Not sure what you mean by saying: "Should I use a variable resister in my circuit to prevent the batteries from draining?"