Voltage buffer arduino voltage sense

Question

I am using a resistor divider to an analog pin on Arduino to sense the voltage of a battery. I've recently been going through my IC's and found a device that can be used as a voltage buffer. I am aware that a voltage buffer spits out what it gets in, so 5V in is 5V out. However, I am unclear on:

A voltage buffer amplifier is used to transfer a voltage from a first circuit, having a high output impedance level, to a second circuit with a low input impedance level.

Further, will this benefit my resistor divider given that their might be fluctuations in load on the circuit due to devices drawing more or less power causing inaccurate measurements?

Please explain as if I am a layman, I'm just starting to get into more advanced electronics aside from connecting pins together.

Answer 1

Roughly, your quote means that a buffers main purpose is to provide current sink/source capacity for a given output, translating to, for example, less susceptibility to noise and more tolerance to various loads.

Regarging your worries on affecting the voltage and fluctuations:

^{simulate this circuit – Schematic created using CircuitLab}

As per Atmega328 datasheet, page 244, the Analog Input will be happy with an input impedance of 10kOhm or less.

Which means that if you manage to keep R1 and R2 in the few kOhm range you will be fine.

Note that the buffer cannot isolate the battery nor the resistive divider from fluctuations caused by the rest of your circuit, it will only "reproduce them" with higher current drive capability. So, if the load of the divider(Vbat/(R1 + R2)) is low enough to not affect the total load (which probably is the case), the buffer will be of little use.

In summary, make R1+R2 too large and they'll be susceptible to noise and charge the sampling caps slower. Make them too small and they might start loading your system a bit. (Although this second scenario is much less likely)