LEGO Train Sensor Solution

[Anobium]

Multiple Hall Switch Monitor for GCBASIC

Overview

This is a Multiple Hall Switch Monitor for the train track teaching solution I am building. This can support 14 hall sensors. I am using seven at the moment. The map below shows the placement of the hall sensors. The logic for the placement will become obvious when I post more later.

---

Main Train Track Map

                -------------------------------------------O-----------------------------------   
            =                                                                                    = 
          =                                                                                         = 
        =                                                                                             = 
      =                                                                                                 = 
     =                                                                                                   = 
    =                                                                                                     = 
   =                                                                                                       = 
  =                                                                                                        = 
  =                                                                                                        = 
  =                                                                                                        = 
   =                                                                                                       = 
   O                                                                                                       O 
    =                                                                                                     = 
     =                        ----O--------------------------------------O------                        = 
      =                     =                                                      =                    = 
        =                 =                                                         =                 = 
           =            =                                                             =             = 
              --------------O-----------------------------------------------------O---------------   

Legend

• = : Parallel track lines (main rail path)
• - : Horizontal rail Parallel track lines
• O : Sensors
• Blank spaces: Open areas or spacing for layout clarity

---

Overview

This program monitors hall effect switches connected to an LGT8F328P microcontroller. It uses pin change interrupts with simple debounce logic to detect state changes and report them over UART.

• Channels 0–5: A0–A5 (PC0–PC5) via PCINT1
• Channel 6: D2 (PD2) via PCINT2
• Channel 7: D3 (PD3) via PCINT2
• Active‑low inputs with internal pull‑ups enabled
• Interrupt‑driven with 10ms debounce inside ISRs
• Sends packets: 0xFF + channel (0–7) + state twice for redundancy
• Startup message + initial states sent automatically
• LED on PB5 (digital pin 13) pulses for 10ms on any change

Target: LGT8F328P @ 32 MHz
Compiler: GCBASIC

---

UART Configuration

#DEFINE USART_BAUD_RATE 9600
#DEFINE USART_TX_BLOCKING
#DEFINE USART_DELAY 10 us

---

Chip and Compiler Settings

#chip LGT8F328P, 32
#option Explicit

---

Pin Constants

#define LED_PIN PORTB.5

---

Variables

Dim OldHallState As Byte
Dim ChangeFlags As Byte
Dim channel As Byte
Dim mask As Byte
Dim state As Byte

---

Subroutine: SendPacket

Sub SendPacket(pSensor As Byte, pState As Byte)
    HserSend 255
    HserSend pSensor
    HserSend pState
    HserSend 255
    HserSend pSensor
    HserSend pState
End Sub

---

Subroutine: InitPins

Sub InitPins
    Dir PORTC In
    PORTC = 0B00111111      ' Pull-ups on PC0-PC5 only

    Dir PD2 In
    Dir PD3 In
    PORTD.2 = 1
    PORTD.3 = 1

    Dir LED_PIN Out
    Set LED_PIN Off

    OldHallState = PINC And 0B00111111
    If PIND.2 = 1 Then OldHallState = OldHallState Or 0B01000000
    If PIND.3 = 1 Then OldHallState = OldHallState Or 0B10000000

    For channel = 0 To 7
        mask = FnLSL(1, channel)
        Dim pin_low As Bit
        If channel < 6 Then
            pin_low = ((PINC And mask) = 0)
        Else If channel = 6 Then
            pin_low = (PIND.2 = 0)
        Else
            pin_low = (PIND.3 = 0)
        End If
        state = 0
        If pin_low = 1 Then state = 1
        SendPacket channel, state
    Next
End Sub

---

Interrupt Service Routines

ISR for PORTC (Channels 0–5)

Sub ISR_PortC
    Wait 10 ms
    Dim current As Byte
    current = PINC And 0B00111111
    Dim changed As Byte
    changed = current Xor (OldHallState And 0B00111111)
    If changed <> 0 Then
        ChangeFlags = ChangeFlags Or changed
        OldHallState = (OldHallState And 0B11000000) Or current
    End If
End Sub

ISR for PORTD (Channels 6–7)

Sub ISR_PortD
    Wait 10 ms
    Dim current_mapped As Byte
    current_mapped = 0
    If PIND.2 = 1 Then current_mapped = current_mapped Or 0B01000000
    If PIND.3 = 1 Then current_mapped = current_mapped Or 0B10000000
    Dim changed As Byte
    changed = current_mapped Xor (OldHallState And 0B11000000)
    If changed <> 0 Then
        ChangeFlags = ChangeFlags Or changed
        OldHallState = (OldHallState And 0B00111111) Or current_mapped
    End If
End Sub

---

Main Program

InitPins

PCICR.1 = 1
PCMSK1 = 0B00111111

PCICR.2 = 1
PCMSK2 = 0B00001100   ' PD2 and PD3

On Interrupt PinChange1 Call ISR_PortC
On Interrupt PinChange2 Call ISR_PortD

INTON

Do
    If ChangeFlags <> 0 Then
        For channel = 0 To 7
            mask = FnLSL(1, channel)
            If (ChangeFlags And mask) <> 0 Then
                Dim pin_low As Bit
                If channel < 6 Then
                    pin_low = ((PINC And mask) = 0)
                Else If channel = 6 Then
                    pin_low = (PIND.2 = 0)
                Else
                    pin_low = (PIND.3 = 0)
                End If
                state = 0
                If pin_low = 1 Then state = 1
                SendPacket channel, state
                ChangeFlags = ChangeFlags And Not mask
            End If
        Next
        PulseOut LED_PIN, 10 ms
    End If
Loop

End

[Anobium]

Below is the PC application shows the real time sensor state: the sensors show the position of the train as it passes over the sensor. The position controls points and other functional parts of the overall solution.

There are other track sections but the are not monitored.