Aquarium air pump and doser on an Arduino Uno

// Aquarium pumps: a 12 V air pump that runs all the time and a 12 V
// peristaltic pump that doses 5 ml of plant food on a timer.
//
//   pin 9   the air pump's D4184 module TRIG
//   pin 10  the dosing pump's D4184 module TRIG
//   a 12 V adapter into both modules' VIN; the Uno's GND to their GND
//
// Neither pump can run from a pin: the air pump draws about 300 mA and the
// dosing pump about 250 mA, at 12 V. A pin switches each module's MOSFETs.
//
// A peristaltic pump moves the same volume every turn, so a dose is a time.
// This one moves 100 ml a minute at 12 V, 1.67 ml a second: 5 ml is 3 s.
// Measure yours the same way (run it 60 s into a measuring cup).
//
// The real doser runs once a day; here "a day" is 20 seconds so you can
// watch it.

const int AIR = 9;
const int DOSE = 10;

const unsigned long ML_PER_MINUTE = 100;
const unsigned long DOSE_ML = 5;
const unsigned long DOSE_MS = DOSE_ML * 60000UL / ML_PER_MINUTE;
const unsigned long DAY_MS = 20000UL;

unsigned long lastDose = 0;
unsigned long doseStarted = 0;
bool dosing = false;
int doses = 0;

void startDose() {
  dosing = true;
  doseStarted = millis();
  digitalWrite(DOSE, HIGH);
  Serial.print("dosing ");
  Serial.print(DOSE_ML);
  Serial.println(" ml");
}

void setup() {
  pinMode(AIR, OUTPUT);
  pinMode(DOSE, OUTPUT);
  Serial.begin(9600);
  digitalWrite(AIR, HIGH);
  Serial.println("air pump on");
  lastDose = millis();
}

void loop() {
  unsigned long now = millis();
  if (!dosing && now - lastDose >= DAY_MS) {
    lastDose = now;
    startDose();
  }
  if (dosing && now - doseStarted >= DOSE_MS) {
    digitalWrite(DOSE, LOW);
    dosing = false;
    doses++;
    Serial.print("done, ");
    Serial.print(doses * DOSE_ML);
    Serial.println(" ml so far");
  }
}