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DIY pH Controller schematic (Arduino)

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Monsta

New Member
Hello everyone,
I am very new to electronics and require some help.
Im building a pH controller using op-amp and arduino microcontroller. I found some schematics on how to set it up. PH Meter - ProjectWiki
The problem is that the above circuit requires 12 or14V to operate, and I wish to run it directly from arduino (only +5V). Output of the whole circuit also needs to be 0V -5V to be able to interface with arduino. It would be very appreciated if someone could recomend the most simplest way to achieve the two requirements. (schematic would be best).
Here is actually a schematic that seems to be what I am looking for: http://www.electro-tech-online.com/threads/ph-probe-op-amp-circuit-problem.9419/
The input voltage is +5V. I just do not know what the output voltage range is?

Thanks!
 

bryan

Member
Contact Richard.C on this board. He has done a PH meter for a pic and am sure he would offer you any help. He has a schematic etc.
 

Monsta

New Member
Wow, that is the most detailed and complete project for diy pH controllers available. Thanks a lot Richard!
 

Monsta

New Member
I was able to find most of the parts locally and the rest Ive ordered. The only problem I am having is the LF356 J-FET OP-AMP. There were only LF356M and LF356N models and data sheet was not helpfull in figuring out their difference. I ordered both just in case; Will either one of them work? What is their difference? Thanks
 
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richard.c

New Member
Hi,

Oops, sorry, made an assumption on the parts list.

The difference is in the package, you want the LF356N - that is the 8 pin DIP type.
The M type is a surface mount device.

Its the same with the other two chips, you want the DIP versions.
 

bhulokapala

New Member
It works!! Thx a lot, Richard!!

Anyway, I didn't find capacitor for C2 & C3, so I replaced them with capacitor 3p for C2 and 6p for C3. Will it be problem?
 

richard.c

New Member
Hi,

Glad it works well for you.

Most caps have a tolerance between 5% to 20% so those values should still be fine.
 

bloodworm

New Member
Hi, I know this post is old but still...
I'm in the process of buying the components for this meter and I would like to know what impedance is needed for the BNC connector. Is it 50 Ohms ?
 

rizz

New Member
Hi,

Glad it works well for you.

Most caps have a tolerance between 5% to 20% so those values should still be fine.
Hey Richard.c, thank you so much for your schematic, its's very common i can buy those components at my hometown.
i want to ask you, how much voltage is in the output ?
mine is 3.5V, is it the right voltage ?

i'm using arduino uno and using the program that i get when i bought ph probe, but the value is always up and down
i want to know if there's an error in my program
 

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spec

Well-Known Member
Most Helpful Member
Hy rizz,

Welcome to ETO. I see you are from Indonesia: care to put it next to 'Location' on your user page so that it displays in the window at the left of your posts.

It is not clear what you are saying.

I suspect that you have bought a standard Arduino and PH shield rather than building Richard's circuit and writing your own sketch (software).

spec
 
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JimB

Super Moderator
Most Helpful Member
Hey Richard.c, thank you so much for your schematic, its's very common i can buy those components at my hometown.
i want to ask you, how much voltage is in the output ?
mine is 3.5V, is it the right voltage ?
Richard.c has not visited the forum for about 3 years, he may not see your request.

JimB
 

Wp100

Well-Known Member
If you look at the original project pdf you will see how the ph amp output voltage has to be read by the 1024 ADC and then coverted to a PH value.

000011.jpg

Taking the code you show, removing the complex averaging for clarity, by adding the new line in Bold type you should get a valid reading.

As to how you are getting 3.5v from that board, where is your ph probe - is it in solution, have you calibrated the board as that pdf shows ?




( mod - sorry - code tags not appearing on toolbar ??)

#define SensorPin A1 //pH meter Analog output to Arduino Analog Input 0
unsigned long int avgValue; //Store the average value of the sensor feedback
float b;
int buf[10],temp;

void setup()
{
pinMode(13,OUTPUT);
Serial.begin(9600);
Serial.println("Ready"); //Test the serial monitor
}
void loop()
{
int adcValue = analogRead(SensorPin);
float phValue = 0.02 * adcValue; // convert ADC reading tp PH value
Serial.print(" pH:");
Serial.print(phValue,2);
Serial.println(" ");
digitalWrite(13, HIGH);
delay(1000);
digitalWrite(13, LOW);

}
 

absam717

New Member
hey in Richard circuit i didn't see any Vcc givent last two opamps U2b, U2C,U2D explain why.i am trying to make a ph meter myself ,so i simulated this in proteus and i got no output .please help
 

DerStrom8

Super Moderator
hey in Richard circuit i didn't see any Vcc givent last two opamps U2b, U2C,U2D explain why.i am trying to make a ph meter myself ,so i simulated this in proteus and i got no output .please help
U2B, U2C, and U2D are all parts of a quad op-amp in a single package (the TL084) which has only one pair of power pins. These power pins supply U2A, U2B, U2C, and U2D. You have to make sure Proteus is configured to supply all of these parts with the one pair of power pins.
 

absam717

New Member
could you send me the the actual circuit diagram and would it be ok to take the output from your circuit and give it to analog pin of an arduino,and display calculated result on screen or should i use an adc before giving output to arduino.how much volt is the output
 
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