How to convert a differential analog signal (-4/+4V) to single ended analog input at Arduino (0-5V)

[tr1n1ty2435]

Hello
I have a differential analog signal with voltage limits of -4/4 V. My aim is to read the signal via the analog input from the Arduino but I’m struggling with the conversion to single ended input (0 - 5V) (my idea was a differential amplifier).
I’m relatively new to the subject and not entire sure if that’s the right way.

[DaveX]

Did you find this thread?

@johnerrington

1: Measuring voltages with an Arduino

Operational amplifiers are simply devices that amplify the difference between two inputs. However these simple devices can be used in combination to create many useful circuits. If you want to measure a signal voltage with an Arduino, you may face some of the issues described here; often a simple circuit using an operational amplifier can help.

[gilshultz]

You could use an RS232 receive IC there are many available. Personally, I would use something like an LM358 and connect the signal to each input via two 27K resistors. If your logic is reversed, simply swap the + and - connections to the op-amp. Try this approach and see if it helps. Also, use 5V instead of 12V.

The outputs will not necessarily go to 0 and 5V but it will be within logic threshold levels.

[ledsyn]

Just a DC signal?

[zwieblum]

You could use 6 resistors: 2 to create 2.5V aka virtual GND from Arduino, 4 to create two 1:2 voltage dividers and virtual GND on the signal side. Connect both virtual GND and use 2 analog inputs for the divided signals.

[DaveX]

I think OP is looking for an an analog signal, mapping a +/-4V differential analog signal into a 0-5V analog signal.

@johnerrington's thread (linked above) has this opamp circuit:

@johnerrington

Difference amplifier

This simply measures the DIFFERENCE between the two inputs and multiplies it by a gain factor. A difference amplifier is used in our second example (Reply 8)

Vo = (Vb - Va) (R2/R1) ;

...but it would need a change to move the 0V reference up to 2.5V. Somewhat like this stackexchange circuit:

Per the thread linked above, you need a dual supply to handle the -4V input:

@johnerrington

The most important criterion is that

the inputs to your circuit must not exceed the bounds of the power supplies.

For example in Fig 5a if you are using +15V - 15V for the supply then you can reasonably apply a 10 volt peak to peak sinewave and you will see the same at the output.

If the SAME op amp is used with a single supply (Fig 5b) +30V - 0V it wont work - and you will likely damage the IC - because the negative excursion of the AC input is outside the range of the supplies.

[6v6gt]

Depending on your requirements for accuracy you may be able to use a solution like this for an AC signal :

You may have to apply a formula to convert the analog value thus obtained to obtain a mapping -4v/+4v to 0v/5v or otherwise interpret the results.

[DaveX]

@6v6gt

Depending on your requirements for accuracy you may be able to use a solution like this for an AC signal

Yes -- What sort of signal is the input signal? How fast does it change?

[TomGeorge]

Hi, @tr1n1ty2435
Welcome to the forum.

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Can you please tell us the source of the -4 to +4 signal?

Thanks.. Tom....

[maikarg]

sloa097.pdf

[GolamMostafa]

There is bi-polar input signals; but, the OP-amp is using single power supply; should it not be dual power supply: +12V/-12V?

[tr1n1ty2435]

Thanks, the information helped a lot

[tr1n1ty2435]

it is an ecg signal, which is amplified by the factor 1mv = 1V and it changes fast

[tr1n1ty2435]

thanks, will try this out

[ledsyn]

@tr1n1ty2435

ecg

And that is...

[jim-p]

Do you know how to read a schematic?

[maikarg]

For ecg there is a module wich works fine and it s inexpensive.

To apply offset for a eeg amplifier I used something like this:

You might want to add a zenenr annd a schottky for protection.

[TomGeorge]

Hi,
Have you Googled;

arduino ecg

Tom....