741 vs LM358 on 5 V

// A 741 and an LM358 on the same 5 V, both as followers of one knob.
//
// A follower has its output wired straight back to its - input, so its gain
// is exactly 1: the output should copy the + input, whatever the knob sets.
// The meter on the left reads the LM358's output, the one on the right the
// 741's.
//
// Turn the knob from one end to the other:
//
//   knob    LM358   741
//   0.00 V  0.005 V 1.50 V
//   2.50 V  2.50 V  2.50 V
//   5.00 V  3.50 V  3.50 V
//
// In the middle both are perfect. Near the ends they are not, and they are
// not wrong in the same way. The LM358 is a single-supply part: its output
// goes all the way down to ground but stops 1.5 V under its supply. The 741
// is a split-supply part, made for +-12 V or +-15 V: its output stops 1.5 V
// short of BOTH rails, so on 5 V it lives between 1.5 V and 3.5 V and nothing
// near ground ever comes out of it.
//
// That is why a 741 circuit copied from a textbook (drawn on +-15 V) does not
// work on an Arduino's 5 V, and why the LM358 is the op-amp in most kits.
//
// The two chips do not share a pinout either. The LM358 has two amplifiers,
// with 1OUT on pin 1 and the supply on pins 8 and 4. The 741 has one, with
// OUT on pin 6, V+ on pin 7 and V- on pin 4; pins 1 and 5 are for an offset
// trimmer and pin 8 is not connected.