I like dlloyd’s solution, post number 9. Simple & effective
every arduino “experiment kit” is different, but all you need is a couple of same value resistors (say 2* 1k - 2*10k) to provide a mid-point voltage; and I’d add a capacitor from mid-point to ground just to decouple;
and a 100k to protect the arduino ADC input.
That 100k is too large, 10k is better, as the ADC is not characterized to perform as per the datasheet
unless the source impedance is 10k or less. Frankly the two resistors giving the mid-rail voltage are
also providing protection so its moot if you need the third resistor, but resistors are cheap.