Help me understand op-amps use

[GolamMostafa]

I am sure if OP has said that his pressure sensor delivers differential signal. If that is the case, then he can nicely use the HX711 Module (Fig-1).

Figure-1:

[Wawa]

Yes, but if he doesn't have a HX711 module,
then why not order a HX module with the sensor already on it.
Leo..

[abdusalam7474]

I just learned about amplifiers. I designed a summing amplifier that outputs 0v when input is 0.001v and outputs 5v when input is 0.075v.

I have included the picture of the amplifier.
Please help me to verify it and suggest improvements that can be made.
Thanks

[jremington]

How is this a bootloader question?

[Coding_Badly]

Thread moved.

[jhaine]

Supply voltage? Why do you need a summing amplifier? Summing amps usually sum at the negative input of the opamp as a virtual earth.

[jremington]

[jhaine]

I did say usually. Design of the non inverting type is more involved.

[johnerrington]

@abdusalam7474

suggest improvements that can be made.

You need to start by learning and being able to apply ohms law.
so what is the current in R2 when V = 0.001V

then kirchoffs laws.
so what is the potential at the junction of R1 & R2 when V = 0.001V

Kirchhoff's Laws - Kirchhoff's Current Law, Kirchhoff's Voltage Law, Solved...

Then the basics of op amps

Using Operational Amplifiers in your Arduino project

Introduction: Using Op Amps to measure signals with an Arduino Who is this tutorial for? Well, not "newbies" or anyone happy to just connect together modules. If you have a LITTLE knowledge of electronics, have perhaps used a transistor or a FET to extend the output capability of an arduino, and want to learn about ways to handle different Analog inputs, than read on! What will you need? All you will need to carry out a few simple experiments is a breadboard, a couple of (very inexpensive) …

and

Remember, for any finite voltage at the output the difference voltage at the input must be zero.

and also that a "real" op amp is not able to produce much current at the output;

and that you cant buy a 15.97 k resisitor off the shelf

[DVDdoug]

When I see mV (or uV) I get worried... With low voltages, noise/instability often becomes a problem.

Any existing noise gets amplified by the amplifier and the amplifier itself adds SOME noise so high-gain amplifiers tend to be "worse".

And to get all the way down to zero volts (or very-near zero volts) you should have bipolar power supplies. Bipolar power supplies are pretty standard with op-amps but with digital we don't usually have a handy negative supply so it has to be added.

[johnerrington]

@DVDdoug

And to get all the way down to zero volts (or very-near zero volts) you should have bipolar power supplies.

of course I agree - but since (I'm guessing) the op wants to feed this to a high impedance analog input, there will be "no" current demand on the op amp so a single supply will work (provided he picks suitable resistor values)

Its a trade-off to keep it simple as we usually dont have a negative supply.

[build_1971]

Maybe OP can offset his input and output to 2.5V...
An opamp will never reach 0V (without bipolar power source) and linearity is also not guaranteed...

[johnerrington]

@build_1971

@build_1971

An opamp will never reach 0V (without bipolar power source)

why not? if there is no (or negligible ) current into the output?

MCP6022: 4.2 Rail-to-Rail Output
The maximum output voltage swing is the maximum
swing possible under a particular output load. According
to the specification table, the output can reach within
20 mV of either supply rail when RL = 10 k

@build_1971

Maybe OP can offset his input and output to 2.5V...

if you've seen this thread, I think thats a fair assumption

Help me understand op-amps use

I have a pressure sensor (MSP40 - GDF) that i want to use in my project. The pressure sensor outputs a max voltage of 75mV. I know I need to boost this to voltage measurable by arduino (Nano). I have choosen LM358 for this task. But Something isn't clear to me: First Question: From my understanding of voltage measurement in arduino: 0v = 0 5v = 1023 (integer rep) if I boost the voltage from my sensor by a factor of 50 then the Max voltage will be 3.75v. This would be 767.25 (max). I would …

[build_1971]

Op requires a 0V output when....
20mV is not 0V...

OK, I must admit the specs of this opamp are pretty impressive and indeed very close to rail to rail...

[Ballscrewbob]

Your two topics on the same or similar subject have been merged.

Please do not duplicate your questions as doing so wastes the time and effort of the volunteers trying to help you as they are then answering the same thing in different places.

Please create one topic only for your question and choose the forum category carefully. If you have multiple questions about the same project then please ask your questions in the one topic as the answers to one question provide useful context for the others, and also you won’t have to keep explaining your project repeatedly.

Repeated duplicate posting could result in a temporary or permanent ban from the forum.

Could you take a few moments to Learn How To Use The Forum

How to get the best out of this forum

See also FAQ - Arduino Forum for general rules on forum behavior and etiquette. Hello, Welcome to the Arduino Forum. This guide explains how to get the best out of this forum. Please read and follow the instructions below. Being new here you might think this is having rules for the sake of rules, but that is not the case. If you don’t follow the guidelines all that happens is there is a long exchange of posts while we try to get you to tell us what we need in order to help you, which is frus…

It will help you get the best out of the forum in the future.

Thank you.

[abdusalam7474]

Good evening everyone. Thanks for your help and suggestions. As mentioned by @Wawa, my sensor generates a differential output of between 10mv and 75mv.

I tried using a differential amplifier like the one in the pic below:

The differential amplifier works for v1-v2 = 1.7 volts (using lM358 op-amp).
But I am facing problems when v1-v2 = 0.012. In this case the op-amp Vo is always equal to 0.63 no matter what I do. I replaced 10k resistor with 1k and 22k resistor with 62k (expecting Vo to be appr = 1.2v). But it still stayed at 0.63v.
Please what am I getting wrong?

[build_1971]

What are the absolute values of v1 and v2? Are they still around 3.6V?
Is there any load on the opamp output? (Apart from a digital multimeter?)

[johnerrington]

@abdusalam7474

(using LM358 op-amp

Are you using a real circuit or is this still just simulation?
And if it IS real where did you buy that 7 digit DVM?

@abdusalam7474

Please what am I getting wrong?

you are not using an op amp designed for low voltage single supply rail-rail operation.
And you are ignoring advice. EG

@johnerrington

You can use an MCP6002

[GolamMostafa]

Would be good to see the equations for Vo of both types of adders of post #27.

[herbschwarz]

I think that the differential amplifier circuit is meant to be powered by plus and minus supplies. You are using ground as the negative supply and starving the input circuit from proper operation. (The LM358 is not a good choice for that circuit.)