Simple op-amp circuit

Other Hardware General Electronics
21

I rewired the circuit by connecting v- of the amp. to Arduino's GND through the 10k resistor.

That doesn't make much sense.

Draw out the circuit you are using with pencil and paper, then either scan it or take a pic with your cell phone. If you use "REPLY" rather than "Quick Reply" you will be presented with options to post a picture or file.

For a great general overview of photodiode circuits and amplifiers, see this application note: http://ecee.colorado.edu/~ecen4827/hw/hw1/PhotodiodeAmplifers.pdf

22

Belal1987:
Thank you all. I rewired the circuit by connecting v- of the amp. to Arduino's GND through the 10k resistor.

The voltage measured between v- and output is exactly how i wanted it to be (Doesn't max under low lights), however, readings in Arduini do not correlate to the amount of light. I think this is because Arduino's GND is different than (e.g. there is a resistor) the GND wired to the voltage meter. Any idea how to overcome this issue?

BTW. how can i attach a pic to a reply? is that possible?

B.

You are welcome!
And I am glad we got Step #1, the Amps-to-Volts Op-Amp circuit, working.

Now, Step #2 ...
But BEFORE, you connect the Op-amp to the Arduino we need to discuss a few things.
Slow down, take breath and explain what you PLAN to do.
Can you re-post your drawing with the change you made?

  1. You need to show us how you PLAN to connect the Op-Amp circuit to the Arduino Analog Input.

  2. Explain why you think the Arduino Ground and Op-Amp Ground can not be the same?

  3. What voltage are you now using to Power the Op-Amp?
    Did you use 4 X AA batteries = 6 Volts ?
    Or did you use the 5 Volts from the Arduino?
    I need to know this before you connect any more wires.

  4. Why did you use BATTERIES vs Arduino 5V in your original drawing?

If you are now using Arduino 5 Volts to power the Op-Amp then I suggest this ...
Pin #4 of the Op-Amp, should be Common Ground to Arduino Gnd.
Pin #1 of the Op-Amp, should be the Volts Output to Arduino Analog input.
per your original drawing.

You see, there is much to discuss before connecting any more wires ...

23

jremington:
What is a "licor sensor"?

Alcohol sensor? (maybe licor -> licquor -> alcohol -> fun!)

24

AlxDroidDev:
Alcohol sensor? (maybe licor -> licquor -> alcohol -> fun!)

The Licor sensor the OP is using, similar to this: LI-210R Photometric Sensor | LI-COR Environmental

25

@mrsummitville thanks a lot,

  • I'm using arduino's 5v now. I used batteries because i though i can use them to get an output range (0-2.5v) but i was wrong.

  • I think the ground should the the same, i'm just confused as where to go with the 10k resistor.

  • Yes i'm getting signal to the arduino from pin 1. Please see attached picture.

  • the purple and the gray wires coming from the BNC connector are inputs from the Li-cor sensor.

Do you think the 10k resistor should be between pin1(amp) and A0(arduino)?

1.JPG
1.JPG1742×640 146 KB

26

Hi,

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

A picture of your layout is fine but hard to trace what goes where and where your arduino and power supply are.

Thanks.. Tom....... :slight_smile:

27

@ TomGeorge, @jremington: attached is the circuit.

Thank you,
Belal

Circuit.JPG

28

V- AND +in have to be grounded.
Make sure the Li-cor sensor is connected with the right polarity.
Leo..

29

Did you notice the outputt connection to analog in is not shown.
Also, it is drawn showing the 10 k resistor in series with the op am - voltage (gnd) which is wrong. I don't know where the 10 k resistor belongs but I know where it doesn't belong, namely, in series with the op amp return (gnd).

30

Belal1987:
@mrsummitville thanks a lot,

  • I'm using arduino's 5v now. I used batteries because i though i can use them to get an output range (0-2.5v) but i was wrong.

  • I think the ground should the the same, i'm just confused as where to go with the 10k resistor.

  • Yes i'm getting signal to the arduino from pin 1. Please see attached picture.

  • the purple and the gray wires coming from the BNC connector are inputs from the Li-cor sensor.

Do you think the 10k resistor should be between pin1(amp) and A0(arduino)?

OK, great you are using the Arduino +5V supply.

But in message #13, I wrote this ...
Your original circuit is almost correct.
You need to connect Pin 3 to Pin 4 of the AD822 OP Amp.
This makes the circuit a Current-To-Voltage converter.

But I still do not see a JUMPER between Pin #3 and Pin #4 of the OpAmp chip.
This jumper is required to complete the Current-To-Voltage Converter circuit

No, do not use a 10K Resistor between Arduino GND and PIN #4 Op-Amp GND
Directly connect the Arduino GND to Pin #4 of the Op-Amp with a wire.
You need a Common Ground Connection.

No, do not use a 10K Resistor between Arduino A0 and PIN #1 Op-Amp Output
Directly connect the Arduino A0 to Pin #1 of the Op-Amp with a wire.

I will repeat this ( from message #21 ) ...
Connect Pin #4 of the Op-Amp directly to Arduino GND
Connect Pin #1 of the Op-Amp directly to Arduino A0 (Anaolog Input)
"Directly Connect" means use a WIRE, not a 10K resistor.

31

@mrsummitville, thank you!
I connected GND of the amp. to arduino's GND directly, i connected pin 3 and 4 directly, and connected pin 1 directly to arduino A0. The output is string of zeros, when i turn on a table lamp, it outputs 8,9,etc. So i think these readings are responsive to the amount of light that falls on the sensor.

Right now i only have one resistor in this circuit which is the one between input and output. Other op-amp circuits have two resistors, is that normal or do i need a second resistor?

Thanks again,
Belal

32

You're looking in the wrong place. This is an Arduino forum. Yes, we also know about op amps.
The question is : "Why are you asking an arduino forum about op amps instead of Googlng "op amp circuits" ? (/configurations/"current to voltage converter")

33

Hi,

Why are you asking an arduino forum about op amps instead of Googlng "op amp circuits" ?

Yes, should have googled, but it is about interfacing with ARDUINO, among other things what else would General Electronics in this forum be about.

We might learn something about how to use these sensors.
The OP isn't the first and won't be the last.

Tom.... :slight_smile:

34

Why are you not wired like so?

Opamp buffer.jpg
Opamp buffer.jpg960×720 25.5 KB

35

Like this:

OP AMP NON-INVERTING AMPLIFIER

36

It's like an echo ...

37

It's like an echo ...

Yeah, it did seem like that but my point was that the OP could have found that with Google, if he knew what to look for but I don't think that's what he needs anyway since the sensor is a current source and I believe someone already told him to use a current to voltage converter (TomGeorge ?)

Actually, this post is still not on track. The OP's posted a link to the datasheetfor the sensor that gives it's output as current "40 uA/100 klux ", so it is a current source and should be used with an op amp
op amp current to voltage converter (which I believe someone else has already pointed out)

38

So it needs a resistor from the + input to Gnd. Not a big deal.

39

see Reply#29

Somewhere in this thread I read that the sensor max output voltage is 10 mV
The feedback resistor should be 500 k ohm (or 499 k)
and the sensor should be applied between V+ and GND , not between V+ and V-.
This is not a Differential Amplifier application, this is a current to voltage converter application.
See op amp circuit link in Reply#36

40

Belal1987:
@mrsummitville, thank you!
I connected GND of the amp. to arduino's GND directly, i connected pin 3 and 4 directly, and connected pin 1 directly to arduino A0. The output is string of zeros, when i turn on a table lamp, it outputs 8,9,etc. So i think these readings are responsive to the amount of light that falls on the sensor.

Right now i only have one resistor in this circuit which is the one between input and output. Other op-amp circuits have two resistors, is that normal or do i need a second resistor?

Thanks again,
Belal

OK, so you are getting a reading of 8 and 9 from the Arduino Analog A0 input.
That sounds like "Good News" but those values seem very low because ...
( 9 / 1023 ) x 5 Volts = 43 millivolts

Now, please let's go back to STEP #1 ...
Getting the OpAmp circuit functioning properly BEFORE connecting Arduino Analog input

You never did tell us what Voltage your OpAmp produced when fully illuminated.

Using your Voltmeter ...
What is the voltage between Pin #1 and #4 of the OpAmp when fully illuminated?

That will be the same voltage the Arduino Analog A0 input will measure
When the Licor is fully illuminated, the Output Voltage should be about 4.999 Volts.

30 microamps ( at 100 klux, full sunlight ) x 180K Ohms = about 5 Volts.
Yes, this circuit is that simple !
Are you reading only 43 millivolts on your Voltmeter?
Do see a problem here or not?

Also, do you understand the POLARITY of the Licor sensor?

I understand that you are very anxious to get the Op-Amp connected to the Arduino.
But it is very important to get STEP #1, the Op-Amp circuit,
working properly before advancing to STEP #2, the Arduino.

Then you asked, "Other op-amp circuits have two resistors?"
I am going to be blunt here ...
I do not care about OTHER OpAmp circuits
In message #13 of this thread I posted a link for a working Licor Current-To-Voltage OpAmp Circuit.
See page #2 here ...

Licor_Schematic

That Licor OpAmp circuit will work.
It is a very, very simple circuit, with very few components.

We are now on Page #3 and message #39 of this thread and
you have not yet mastered this simple 3 component Current-To-Voltage OpAmp circuit.
You need to focus on making Step #1 successful first.
You need to ignore the Arduino Analog input, until later.