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Topic: Simple op-amp circuit (Read 8584 times) previous topic - next topic

Wawa

And use 4 AA batteries, instead of 2 AA batteries,
this will make a 6 Volt power supply.
The AD822 OP Amp needs 5 volts minimum.
And you connect the opamp output directly to an Arduino pin?
With the risk of phantom powering.
What is the problem in using Arduino's 5volt supply.
Leo..

mrsummitville

And you connect the opamp output directly to an Arduino pin?
With the risk of phantom powering.
What is the problem in using Arduino's 5volt supply.
Leo..
Because I do not see an Arduino or a 5 Volt Supply in the original schematic.



Wawa

So i'm trying to amplify the signal from a photometric licor sensor and record it with Arduino.
Post#0

raschemmel

#18
Nov 07, 2015, 07:35 am Last Edit: Nov 07, 2015, 12:32 pm by raschemmel
I'm not familiar with that sensor  but without knowing the maximum klux possible (Full Scale) I would have no idea what resistance to use to convert the current source to a voltage source that can be measured with an arduino.
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

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.

jremington

#20
Nov 12, 2015, 03:41 am Last Edit: Nov 12, 2015, 03:47 am by jremington
Quote
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

mrsummitville

#21
Nov 12, 2015, 04:26 am Last Edit: Nov 12, 2015, 04:28 am by mrsummitville
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 ...

AlxDroidDev

What is a "licor sensor"?
Alcohol sensor? (maybe licor -> licquor -> alcohol -> fun!)

Some of my projects:
Shield for DS1337+, DS1624 and AT24C1024B (RTC, temp & mem): http://forum.arduino.cc/index.php/topic,126197.0.html
CHDK Camera remote shutter (BT, IR, USB): http://forum.arduino.cc/index.php?topic=295377.0

mrsummitville

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


The Licor sensor the OP is using, similar to this: http://www.licor.com/env/products/light/photometric.html

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)?

TomGeorge

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....... :)
Everything runs on smoke, let the smoke out, it stops running....

Belal1987

@ TomGeorge, @jremington: attached is the circuit.

Thank you,
Belal

Wawa

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

raschemmel

#28
Nov 13, 2015, 03:32 pm Last Edit: Nov 13, 2015, 03:33 pm by raschemmel
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).
Arduino UNOs, Pro-Minis, ATMega328, ATtiny85, LCDs, MCP4162, keypads,<br />DS18B20s,74c922,nRF24L01, RS232, SD card, RC fixed wing, quadcopter

mrsummitville

#29
Nov 13, 2015, 10:40 pm Last Edit: Nov 13, 2015, 10:54 pm by mrsummitville
@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.







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