Quick Start — Micro PinOS

What you need

🧠

ATmega2560

Game brain board

🔲

ATmega328P Nano ×1–5

One per switch cluster

📡

MAX485 Modules

One per board — RS485 drivers

⚡

MOSFET Drivers

TIP120 or IRLZ44N per coil

🔧

1N4007 Diodes

Flyback protection per coil

🔌

Dual PSU

5V logic + 24–48V solenoid

Step-by-step guide

Download Micro PinOS and open in Arduino IDE

Install the framework and verify your board setup

Download the full bundle from the Download page and unzip. You'll find two folders: Mega/ and nano/. Open Mega/MainMega.ino in Arduino IDE 2.x, select ATmega2560 (or ATmega2560 (Mega 2560)) as the board, and the correct COM port.

Mega/ folder structure

// Mega/
//   MainMega.ino    ← open this file
//   attract.h       ← attract mode + wheel selector
//   GameStyleOne.h  ← traditional scoring (full)
//   GameStyleStubs.h← Styles 2–4 (stub, ready to fill)
//   commands.h      ← all TYPE:PAYLOAD strings
//   switches.h      ← all switch ID #defines

// nano/
//   nano_universal.ino  ← open this for each Nano
//   switch_ids.h        ← shared switch ID constants

Wire the RS485 bus

One MAX485 module per board, four wires shared

The RS485 bus uses four wires between all boards: A, B (the differential pair), GND, and +5V. All Nanos and the Mega share the same A and B lines — this is the multi-drop topology.

Mega: Serial1 (pins 18/19) → MAX485 → bus
Each Nano: Serial (pins 0/1) → MAX485 → same bus
DE/RE pins on all MAX485 modules tied together to D2 on each board
Add 120Ω termination resistors across A/B at each end of the bus

Pin definitions — MainMega.ino

// MainMega.ino — serial port assignments
//   Serial1 (pins 18/19) → RS485 bus → all Nanos
//   Serial2 (pins 16/17) → Sound board (DFPlayer etc.)
//   Serial3 (pins 14/15) → Display / lights board

#define RS485_DE_PIN  2    // MAX485 transmit enable

void setup() {
  Serial.begin(115200);   // USB debug
  Serial1.begin(115200);  // RS485 bus
  Serial2.begin(115200);  // Sound board
  Serial3.begin(115200);  // Display/lights board

  pinMode(RS485_DE_PIN, OUTPUT);
  digitalWrite(RS485_DE_PIN, LOW);  // start in receive

  // Init solenoid pins
  for (int i = 0; i < NUM_SOLENOIDS; i++) {
    pinMode(solenoids[i].pin, OUTPUT);
    digitalWrite(solenoids[i].pin, LOW);
  }
}

Configure your first Nano

Edit the switch table — nothing else needs changing

Open nano/nano_universal.ino. Set MY_ADDRESS to a unique number for this Nano (0–4). Then fill in the switch table at the top — each row is one switch: pin, ID, solenoid pin, hold pin, pulse duration, debounce time.

nano_universal.ino — Nano 0 (Type 2 Reaction)

#define MY_ADDRESS   0        // unique per Nano
#define DE_PIN       2        // MAX485 DE pin — always D2
#define BAUD_RATE    115200

// Type 1 Sensor:   solPin=-1, holdPin=-1
// Type 2 Reaction: solPin>=0, holdPin=-1  (fires local coil)
// Type 3 Flipper:  add #define DUAL_WOUND at top

// pin | switchID           | solPin | holdPin | pulseMs | debounceMs
static const SwEntry SW[] = {
  {  3, SW_SLINGSHOT_LEFT,       5,      -1,      25,           5 },
  {  4, SW_SLINGSHOT_RIGHT,      6,      -1,      25,           5 },
  {  7, SW_POP_BUMPER_TOP,       8,      -1,      20,           5 },
  {  9, SW_POP_BUMPER_LEFT,     10,      -1,      20,           5 },
  { 11, SW_POP_BUMPER_RIGHT,    12,      -1,      20,           5 },
};
// ── NOTHING BELOW THIS LINE NEEDS EDITING ──

For a Type 1 sensor Nano (rollover lanes, targets, cabinet switches), set solPin = -1 and holdPin = -1. The Nano just debounces and reports — no local solenoid fires.

Nano 1 — Rollover lanes (Type 1 Sensor)

#define MY_ADDRESS   1   // Nano 1

static const SwEntry SW[] = {
  {  3, SW_ROLLOVER_F,  -1, -1, 0, 10 },
  {  4, SW_ROLLOVER_I,  -1, -1, 0, 10 },
  {  7, SW_ROLLOVER_R,  -1, -1, 0, 10 },
  {  9, SW_ROLLOVER_E,  -1, -1, 0, 10 },
};

Wire solenoids on the Mega

MOSFET driver per coil — millis() pulse management

Each solenoid on the Mega side uses one N-channel MOSFET (IRLZ44N or TIP120). Gate → Mega digital pin, Drain → coil negative, Source → GND. A 1N4007 flyback diode goes across each coil (cathode to +V).

Solenoid pin definitions — MainMega.ino

// Mega solenoid pin assignments
#define PIN_TROUGH       22   // ball trough kicker
#define PIN_KNOCKER      23   // knocker (game over)
#define PIN_UPPER_L      24   // upper left flipper assist
#define PIN_UPPER_R      25   // upper right flipper assist
#define PIN_SLING_LEFT   26   // left slingshot (also Type 2)
#define PIN_SLING_RIGHT  27   // right slingshot
#define PIN_POP_LEFT     28   // left pop bumper
#define PIN_POP_RIGHT    29   // right pop bumper
#define PIN_POP_CENTER   30   // center pop bumper

#define SOL_PULSE_MS    30    // default coil pulse duration
#define TROUGH_PULSE_MS 60    // trough kicker needs longer

// Fire from game code:
fireSolenoid(IDX_TROUGH, TROUGH_PULSE_MS);
fireSolenoid(IDX_KNOCKER);   // uses SOL_PULSE_MS default

Flash both boards and verify the bus

Upload Mega first, then each Nano

Upload MainMega.ino to the Mega first. Open Serial Monitor at 115200 baud — you should see [ Micro PinOS ] Main Mega ready. and Styles loaded: 4.

Then upload nano_universal.ino to each Nano (change MY_ADDRESS each time). Trigger a switch manually — the Mega Serial Monitor should show the event being received.

Expected serial output on boot

// Mega Serial Monitor output:
[ Micro PinOS ] Main Mega ready.
Styles loaded: 4

// When a Nano switch fires (e.g. slingshot left):
// Mega receives frame "S0:1\n" on Serial1
// dispatchEvent(0, 1) called
// → currentGame->onShot(SW_SLINGSHOT_LEFT)
// → addScore(50), fireSolenoid(IDX_SLING_LEFT)
// → sendSound("SLING") on Serial2

Additional setup notes

Loading additional notes…