Dosing pump on an Arduino Uno

// Dosing pump: a peristaltic pump head on a gear motor with a Hall encoder,
// driven by an L9110S, that pumps a measured dose at the press of a button.
// The aquarium fertilizer doser, the plant feeder and the cocktail machine
// are all this.
//
//   pin 5   the L9110S's A-IA (speed, PWM)   pin 6  its A-IB
//   pin 2   the encoder's A (an interrupt)   pin 3  its B
//   pin 4   the button to GND (INPUT_PULLUP)
//   the pack's + to the L9110S's VCC; the encoder's VCC to 5 V; grounds joined
//
// A peristaltic pump moves the same volume every turn of its rotor, so the
// dose is a number of turns, and the encoder counts them. It gives 11 pulses
// a motor turn through a 30:1 gearbox: 330 pulses on A for each turn of the
// pump. This head moves 0.5 ml a turn (measure yours: pump 20 turns into a
// measuring cylinder and divide), so 5 ml is 10 turns, 3300 pulses.
//
// # Stopping on the mark
//
// A motor does not stop the instant it is told. So the pump runs at full
// speed until it is one turn short, slows to a crawl for the last turn, and
// brakes (both inputs high) a little early, at 45 pulses to go, for the few
// it coasts through. The count goes on after the brake, so the dose printed
// is what actually went through.

const int IA = 5;
const int IB = 6;
const int ENC_A = 2;
const int ENC_B = 3;
const int BUTTON = 4;

const long PULSES_PER_TURN = 330;
// Hundredths of a ml per turn of the pump head.
const long CENTI_ML_PER_TURN = 50;
const long DOSE_CENTI_ML = 500;
const long DOSE_PULSES = DOSE_CENTI_ML * PULSES_PER_TURN / CENTI_ML_PER_TURN;
const long SLOW_AT = DOSE_PULSES - PULSES_PER_TURN;
const long BRAKE_AT = DOSE_PULSES - 45;
const int FULL = 255;
const int CRAWL = 90;

volatile long pulses = 0;

void onA() {
  // B low on A's rising edge is forward.
  if (digitalRead(ENC_B) == LOW) {
    pulses++;
  } else {
    pulses--;
  }
}

long count() {
  noInterrupts();
  long n = pulses;
  interrupts();
  return n;
}

void run(int speed) {
  analogWrite(IA, speed);
  digitalWrite(IB, LOW);
}

void brakeMotor() {
  digitalWrite(IA, HIGH);
  digitalWrite(IB, HIGH);
}

void printMl(long p) {
  long centi = p * CENTI_ML_PER_TURN / PULSES_PER_TURN;
  Serial.print(centi / 100);
  Serial.print('.');
  if (centi % 100 < 10) Serial.print('0');
  Serial.print(centi % 100);
  Serial.print(" ml");
}

void setup() {
  Serial.begin(115200);
  Serial.println("Mokxi Arduino Uno: dosing pump");
  pinMode(IA, OUTPUT);
  pinMode(IB, OUTPUT);
  pinMode(ENC_A, INPUT);
  pinMode(ENC_B, INPUT);
  pinMode(BUTTON, INPUT_PULLUP);
  brakeMotor();
  attachInterrupt(digitalPinToInterrupt(ENC_A), onA, RISING);
  Serial.print("press for a dose of ");
  printMl(DOSE_PULSES);
  Serial.println();
}

void dose() {
  noInterrupts();
  pulses = 0;
  interrupts();
  Serial.println("pumping");
  run(FULL);
  bool slow = false;
  while (count() < BRAKE_AT) {
    if (!slow && count() >= SLOW_AT) {
      run(CRAWL);
      slow = true;
    }
  }
  brakeMotor();
  delay(500);
  long p = count();
  Serial.print("dosed ");
  printMl(p);
  Serial.print(" (");
  Serial.print(p);
  Serial.println(" pulses)");
}

void loop() {
  if (digitalRead(BUTTON) == LOW) {
    dose();
    while (digitalRead(BUTTON) == LOW) delay(10);
    delay(50);
  }
}