An opamp does not need a negative supply if you power it with a positive voltage and ground, then bias its (+) input at half the supply voltage like this:
The very simple opamp circuit uses resistor values calculated from knowledge of opamp spec's (input current) and other opamp circuits (experience).Where I can find the values of the resistors?
Hi,
Reading your last post...
I don't think the problem is which amplifier to choose, which resistor value to choose or which power supply to choose.
To be honest: I think the problems are your electronic skills.
*****
Let's start from the beginning:
* you have an analog input signal
* and you want to feed it to the arduino's ADC (correct me if I'm wrong)
In the following there are a lot of questions...I know this sounds booring, but these are the requirements that tell you (us) which solution to choose. Best is if you can give values with units. Maybe you are not aware of all the answers, then at least try to explain in words.
Now let's define the input signal.
* the absolute input signal voltage range is: from -1.5V to +1.5V.
(if so, then you don't need to amplify the signal)
* what's the signal waveform: pure sine, squarewave, random like audio, please describe it.
* what's the source of the signal?
* what's the source_impedance of the signal?
* what's the signal frequency range?
* are you interested in the DC value of the input signal?
(If not then maybe you don't need an amplifier at all)
Arduino side:
Please tell us what you want to do with the signal?
What values do you want to measure and calculate?
What resolution, precision and accuracy do you want to achieve?
How often do you want to calculate the output values?
(Example: if you want to output your results on a display, then it's sufficient to calulate once per second up to 3 times oer second)
Solutions may be:
* just to re-wire your signal source (no additional part)
* just two resistors
* two resistors and a capacitor
* or an Opamp (difference) amplifier circuit (Opamp with 3, 4 or 5 resistors)
...all may be combined with filters
Klaus
The very simple opamp circuit uses resistor values calculated from knowledge of opamp spec's (input current) and other opamp circuits (experience).
Hi,
My thoughts.
Why the envelope detector in hardware? I find it more flexible and less prone to errors (drift, noise...) when you do this in software.
Klaus
Just add voltage at the analog side and subtract it on the digital side.Is it possible to feed the Arduino, with an audio signal that has positive and negative values?
a choice of such different devices
Hi Brian,
Not likely but beginners boxes come with such delights as a few of each of the following: 7805, 7812, 4001, 4013, 741, 386, 555.
Clearly, these learner kits are not all about offloading unsellable ancient parts noone with an iota of experience would purchase to novices who start the learning curve with prehistoric op amps and junk parts like the 741... But it does have offset null pins, making it really useful.
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