Motor current meter on an Arduino Uno

// Motor current meter: an ACS712 5 A current sensor in a gear motor's lead,
// and the current on a 16x2 I2C LCD.
//
//   A0      the ACS712's OUT (its VCC on 5 V, GND on GND)
//   IP+     from the push button, on the bench supply's plus
//   IP-     to the motor, whose other lead goes back to the supply's minus
//   LCD     SDA -> A4    SCL -> A5    VCC -> 5 V    GND -> GND
//
// The ACS712's output is half its supply with no current and moves 185 mV an
// amp on the 5 A board. The motor's circuit never touches the Arduino's: the
// sensor measures the field the current makes, through the chip's insulation.
//
// Nothing flows until the button is held, so the sketch measures the zero at
// power on with ACS712's autoMidPoint(). Then it averages 50 readings at a time, which
// smooths the sensor's noise, and keeps the highest current it has seen.
// Hold the button and the peak catches the surge a stalled motor draws
// before it spins up; the running current is a few converter steps above
// zero, because one step on the 5 A board is 26 mA.

#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include "ACS712.h"

ACS712 ACS(A0, 5.0, 1023, 185);
LiquidCrystal_I2C lcd(0x27, 16, 2);
float peak = 0;

void setup() {
  Serial.begin(115200);
  Serial.println("Mokxi Arduino Uno: motor current meter");
  lcd.init();
  lcd.backlight();
  lcd.print("Zeroing...");
  ACS.autoMidPoint();
  Serial.print("Midpoint: ");
  Serial.println(ACS.getMidPoint());
  lcd.clear();
}

void showLine(int row, const char *label, float mA) {
  lcd.setCursor(0, row);
  lcd.print(label);
  int whole = (int)(mA + (mA < 0 ? -0.5 : 0.5));
  lcd.print(whole);
  lcd.print(" mA     ");
}

void loop() {
  // For a fifth of a second, take quick averages of ten readings: quick
  // enough to catch the surge for the peak. The screen shows their average.
  float sum = 0;
  int n = 0;
  unsigned long began = millis();
  while (millis() - began < 200) {
    float mA = ACS.mA_DC(10);
    if (mA > peak) peak = mA;
    sum += mA;
    n++;
  }
  float mA = sum / n;
  showLine(0, "Now  ", mA);
  showLine(1, "Peak ", peak);
  Serial.print("mA: ");
  Serial.print(mA, 0);
  Serial.print("  peak: ");
  Serial.println(peak, 0);
}