Lego Points Controller

[Anobium]

This is another part of an implementation of a STEM project inspired and based on Hugh's Australian work.

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Summary

This program controls a single GeekServo servo motor connected to an LGT8F328P microcontroller to operate a railway points system, such as a track switch. The servo, connected to SERVOOUTCHANNEL (PORTC.0), toggles between full clockwise (FULL_CW, 1.25ms) and full counterclockwise (FULL_CCW, 1.75ms) positions to switch the points, triggered by a debounced switch input on SWITCHIN (PORTE.3). A state machine with states CLOCKWISE and COUNTERCLOCKWISE manages servo movement, using pulse width modulation via an adapted PulseOut macro handling WORD time slices. The servo moves in 50µs steps with a 100µs delay for smooth operation. An indicator LED on INDICATOR_LED (PORTB.5) is on for the clockwise position and off for the counterclockwise position. The system enters low-power idle mode when no switch press is detected, reducing power consumption. A configuration script ensures valid pulse widths for the selected POINTSET2 (AVR-specific values) and issues errors or warnings for invalid settings. The choice of the LGT8F328P is not critical; the microcontroller and ports (e.g., SERVOOUTCHANNEL, SWITCHIN, INDICATOR_LED) can be changed to suit your configuration.

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Code

Enjoy

/*
A demonstration program for GCBASIC.
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This program controls a single GeekServo servo motor on an LGT8F328P microcontroller, connected to SERVOOUTCHANNEL
(PORTC.0). It toggles the servo between full clockwise (FULL_CW, 1.25ms) and full counterclockwise (FULL_CCW, 1.75ms) positions
based on a debounced switch input (SWITCHIN on PORTE.3). A state machine, managed by HandleServoState, uses states CLOCKWISE
and COUNTERCLOCKWISE to control servo movement, triggered by polling the switch via funcKeyPressed in the main loop. Each switch
press toggles the servo direction. The servo moves in 50µs steps (5 units) with a 100µs delay between pulses for smooth operation.
An indicator LED on INDICATOR_LED (PORTB.5) is on for the clockwise position and off for the counterclockwise position. The
system enters low-power idle mode when no switch press is detected, reducing power consumption. A configuration script ensures
valid pulse widths for the selected POINTSET2 (AVR-specific values) and issues errors or warnings for invalid settings. USART is
configured at 9600 baud but unused.

Key Components:
- Configuration:
  - Microcontroller: LGT8F328P with #option Explicit for strict variable declaration.
  - USART: Configured at 9600 baud with blocking transmission, but no serial output is used.
  - I/O Pins:
    - SWITCHIN (PORTE.3): Input for switch, active-high (DOWN = 1).
    - INDICATOR_LED (PORTB.5): Output for LED indicating servo direction.
    - SERVOOUTCHANNEL (PORTC.0): Output for the servo motor.
  - Constants:
    - SERVO_PULSE_DELAY (100µs): Delay between servo pulses.
    - DEBOUNCE_DELAY (1ms): Delay for switch debouncing.
    - FULL_CW (125, 1.25ms) and FULL_CCW (175, 1.75ms): Servo pulse widths for AVR under POINTSET2.
  - Script: Ensures only one POINTSET is defined, sets pulse widths, and issues warnings or errors.
  - ENUM: ServoState defines CLOCKWISE and COUNTERCLOCKWISE for the state machine.
- Variables:
  - PulseTime (WORD): Stores the current servo pulse width (in 10µs units).
  - ServoState (Byte): Tracks the state machine state (CLOCKWISE or COUNTERCLOCKWISE).
  - CurrentSwitchState and LastSwitchState (Bit, local to funcKeyPressed): Used for debouncing.
- Main Loop:
  - Polls funcKeyPressed to detect switch presses.
  - On a valid press, toggles ServoState between CLOCKWISE and COUNTERCLOCKWISE and calls HandleServoState.
  - Enters idle mode when no switch press is detected, waking on the next loop iteration.
  - The state machine is handled in HandleServoState.
- Functions and Subroutines:
  - HandleServoState: Manages the state machine:
    - CLOCKWISE: Moves servo from FULL_CW to FULL_CCW, sets INDICATOR_LED on.
    - COUNTERCLOCKWISE: Moves servo from FULL_CCW to FULL_CW, sets INDICATOR_LED off.
  - funcKeyPressed: Debounces the switch, returning TRUE on a rising edge (released to pressed) after a 1ms delay.
  - PulseOut (macro): Generates a servo pulse for localPulseTime × 10µs.
- Operation:
  - On startup, the servo moves to the clockwise position (CLOCKWISE), and INDICATOR_LED blinks 10 times, then stays on.
  - The main loop continuously polls funcKeyPressed.
  - A switch press toggles ServoState between CLOCKWISE and COUNTERCLOCKWISE, calling HandleServoState to move the
    servo and update the LED.
  - When no switch press is detected, the system enters sleep mode to save power, waking on the next loop iteration.
  - The servo moves smoothly between positions with 100µs delays.
- Notes:
  - Polling-Based Switch Handling: Uses polling with funcKeyPressed for simplicity.
  - Power Management: Idle mode when no switch press is detected balances power savings with polling responsiveness.
  - State Machine: The ServoState ENUM ensures proper toggling between CLOCKWISE and COUNTERCLOCKWISE positions.
  - Debouncing: funcKeyPressed ensures robust switch detection with a 1ms delay.

@author     EvanV
@licence    GPL
@version    1.0e
@date       08.21.2025
********************************************************************************/

// ----- Configuration
#chip LGT8F328P                                // Specify the microcontroller model (LGT8F328P)
#option Explicit                               // Enforce variable declaration for better code reliability

#DEFINE USART_BAUD_RATE 9600                   // Set UART baud rate to 9600 for serial communication
#DEFINE USART_TX_BLOCKING                      // Enable blocking mode for UART transmission
#DEFINE USART_DELAY OFF                        // Disable additional USART delays

// ----- Constants
    // Define I/O pins
    #DEFINE SWITCHIN      PORTE.3              // Switch input connected to PORTE.3
    Dir SWITCHIN In                            // Set PORTE.3 as input
    #DEFINE DOWN          1                    // Switch active state (high)
    #DEFINE INDICATOR_LED PORTB.5              // Indicator LED connected to PORTB.5
    DIR INDICATOR_LED OUT                      // Set PORTB.5 as output
    #DEFINE SERVOOUTCHANNEL PORTC.0           // Servo connected to PORTC.0
    DIR SERVOOUTCHANNEL OUT                   // Set PORTC.0 as output

    // Servo pulse width constants (in units of 10µs, specific to GeekServo servo)
    #DEFINE POINTSET2                          // Use POINTSET2 configuration for servo
    #DEFINE DISABLE1173                        // Unused configuration flag
    #DEFINE SERVO_PULSE_DELAY 100 us           // Delay between servo pulses for smooth movement
    #DEFINE DEBOUNCE_DELAY 1 ms                // Delay for switch debouncing

    // Define servo state machine states
    ENUM ServoState
        CLOCKWISE                              // Servo in full clockwise position
        COUNTERCLOCKWISE                       // Servo in full counterclockwise position
    End Enum

#script
    FULL_CW  = 0
    FULL_CCW = 0

    TITLE = ""
    If DEF(POINTSET1) Then
        FULL_CW  = 70                         // 0.7ms for clockwise (POINTSET1)
        FULL_CCW = 120                        // 1.2ms for counterclockwise (POINTSET1)
        TITLE = "POINTSET1"
        Warning "POINTSET1 configuration"
    End If
    If DEF(POINTSET2) Then
        If DEF(PIC) Then
            FULL_CW  = 110                    // 1.1ms for clockwise (PIC, POINTSET2)
            FULL_CCW = 160                    // 1.6ms for counterclockwise (PIC, POINTSET2)
        End If
        If DEF(AVR) Then
            FULL_CW  = 125                    // 1.25ms for clockwise (AVR, POINTSET2)
            FULL_CCW = 175                    // 1.75ms for counterclockwise (AVR, POINTSET2)
        End If
        TITLE = "POINTSET2"
        Warning "POINTSET2 configuration"
    End If
    If DEF(POINTSET3) Then
        FULL_CW  = 120                        // 1.2ms for clockwise (POINTSET3)
        FULL_CCW = 170                        // 1.7ms for counterclockwise (POINTSET3)
        Warning "POINTSET3 configuration"
    End If

    If FULL_CW = 0 and FULL_CCW = 0 Then
        Error "No configuration"
    End If
#endscript

// ----- Variables
Dim PulseTime As WORD                          // Stores the current pulse width for servo control (in 10µs units)
Dim ServoState As Byte                         // Tracks the servo state (CLOCKWISE, COUNTERCLOCKWISE)

// ----- Main body of program commences here.
ServoState = CLOCKWISE                         // Initialize servo state to CLOCKWISE

Dir INDICATOR_LED Out                          // Configure INDICATOR_LED as output for the indicator LED
Repeat 10                                      // Blink INDICATOR_LED 10 times to signal program start
    INDICATOR_LED = !INDICATOR_LED             // Toggle INDICATOR_LED state
    Wait 50 ms                                 // Wait 50ms between toggles
End Repeat
INDICATOR_LED = True                           // Set LED on for initial CLOCKWISE state

// Initialize servo to clockwise position
HandleServoState                               // Move servo to initial position (CLOCKWISE)

// Main loop to monitor and control the servo
Do
    If funcKeyPressed() = TRUE Then            // Check for debounced switch press
        If ServoState = CLOCKWISE Then         // Toggle state: CLOCKWISE to COUNTERCLOCKWISE
            ServoState = COUNTERCLOCKWISE
        Else
            ServoState = CLOCKWISE             // Toggle state: COUNTERCLOCKWISE to CLOCKWISE
        End If
        HandleServoState                       // Move servo to new position
    Else
        Sleep                                  // Enter idle mode when no switch press is detected
    End If
Loop

// Subroutine to handle the servo state machine
Sub HandleServoState
    Select Case ServoState
        Case CLOCKWISE                         // CLOCKWISE: Move servo to full clockwise position
            INDICATOR_LED = True               // Set LED on for clockwise
            For PulseTime = FULL_CW To FULL_CCW Step 5
                PulseOut SERVOOUTCHANNEL, PulseTime, 10us // Send pulse to servo
                Wait SERVO_PULSE_DELAY         // Delay for smooth movement
            Next
        Case COUNTERCLOCKWISE                  // COUNTERCLOCKWISE: Move servo to full counterclockwise position
            INDICATOR_LED = False              // Set LED off for counterclockwise
            For PulseTime = FULL_CCW To FULL_CW Step -5
                PulseOut SERVOOUTCHANNEL, PulseTime, 10us // Send pulse to servo
                Wait SERVO_PULSE_DELAY         // Delay for smooth movement
            Next
    End Select
End Sub

// Function to debounce and detect switch press
Function funcKeyPressed As Bit
    Dim CurrentSwitchState As Bit              // Current state of the switch
    Dim LastSwitchState As Bit                 // Previous state of the switch

    Wait DEBOUNCE_DELAY                        // Wait for debounce period

    // Check if switch is pressed
    If SWITCHIN = DOWN Then
        CurrentSwitchState = TRUE              // Switch is pressed
    Else
        CurrentSwitchState = FALSE             // Switch is released
    End If

    // Detect rising edge (switch pressed)
    If CurrentSwitchState <> LastSwitchState AND CurrentSwitchState = TRUE Then
        funcKeyPressed = TRUE                  // Return TRUE for valid press
    Else
        funcKeyPressed = FALSE                 // No valid press detected
    End If

    LastSwitchState = CurrentSwitchState       // Update last state
End Function

// Macro to generate a pulse for servo control
macro PulseOut (Pin, localPulseTime As WORD, localTimeUnit)
    Set Pin On                                // Set the specified pin high
    Repeat localPulseTime                     // Loop for the specified pulse duration
        Wait 1 localTimeUnit                  // Wait for 1 unit of time (10µs)
    End Repeat
    Set Pin Off                               // Set the pin low to end the pulse
End macro

[Anobium]

This is part of an implementation of a STEM project inspired and based on Hugh's Australian work.

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The switch controller was specifically designed for the project. I have the design in Lego Studio and there is a complete bill of materials and build process. My thanks go to Jack Sisson who has designed this switch control with the a cheap GeekServo servo.

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The views of the build.