Voltage value drop when connected to the analog pin

Projects General Guidance
1

Hello.. first time asking in forum :slight_smile:
Here, i have a problem with the schematic. I want to read the voltage value from GMR NVE AA002 (it has a Wheatstone bridge construction).

Because the output in mV, so I connected output pins from GMR to AD620 amplifier before went to analog pin in Arduino. For the V- and V+ supply on AD620, i use voltage converter from intersil, icl7660.

I could read the AD620 output with multimeter, but when it connected to analog pin, the value on LCD went drop... How could it be like that? I tried again several times through proteus, but still.. Was my schematic wrong?

Any help appreciated. Thank you.

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2

Without looking at your schematic, I would guess that it is an impedance mismatch between the output of the amplifier and the input to the Arduino.

3

I could read the AD620 output with multimeter, but when it connected to analog pin, the value on LCD went drop

Please take a few moments to explain what you mean.

What is "it" that was connected to the analog pin?

What is the "value" on LCD?

What does "went drop" mean? Post example numbers.

The schematic is very confusing and may not be correct -- it does not follow the rules (Vcc at the top, GND at the bottom, does not show inputs to or feedback in the amplifier, etc.).

4

You made a poor choice by using the AD620. It requires dual supplies, so you generate the required negative voltage with an icl7660. This is not a proper supply for an analog circuit, it has far too much switching noise. Worse, the analog input pin of the Arduino cannot tolerate a negative voltage which is possible if the AD620 output goes to its negative rail.

You do not need or want a dual voltage amplifier. Look at the datasheet for your sensor. It's output is always positive. There are several example amplifier circuits shown in the datasheet, none use a dual supply opamp - because it is not needed. A proper rail-to-rail opamp is what is required.

Redesign your amplifier per the device datasheet. That should be the proper starting point for your project.

5

The answers really fast, thank you very much, i will redesign it first and tell how it works..

6

Try a HX711 breakout board.
Onboard 4.3volt excitation output (+E), to provide a stable supply for the bridge.
And instrumentation amps with buildin 24-bit A/D (digital out).
Well supported with Arduino code.
Leo..