Laser timer from Cambridge PiWars

The PiWars timer was built from the following components:

• 2x 1 mW lasers to produce the light beam
• 2x Photo diodes to detect the presence of the light beam
• 2x small tubes which we placed the photo diodes in to block out the surrounding light (aimed at lasers)
• 4x RS485 driver chips:
  Two to convert the signal from the sensor to a + and - pair to send down wires
  Two to convert the + and - pair back to a logic signal for the Raspberry Pi
• Various resistors et cetera to get the correct voltage levels
• Some metal frame to keep the components stable

In case anyone is interested, here is the code we used for the timing:

#!/usr/bin/env python
# coding: latin-1

# Import library functions we need (we are using pigpio so we can get pin change events)
#  See http://abyz.co.uk/rpi/pigpio/download.html for setup of pigpio
import pigpio
import Tkinter
import time

# Set which GPIO pins the sensor beams are connected to
SENSOR_START  = 9   # White
SENSOR_FINISH = 11  # Red

# Settings about the run
trackLength    = 7.31
maxRobotLength = 0.42
sensorDistance = trackLength - maxRobotLength

# Set some state names for GUI reporting
STATE_DONE      = 1
STATE_GO        = 2
STATE_RUNNING   = 3
STATE_FINISHED  = 4

# Global values
global pi
global filePath
filePath = './PiWars_Results.txt'

# Setup the GPIO
pi = pigpio.pi()

# Class representing the GUI dialog
class PiWarsTimer_tk(Tkinter.Tk):
    # Constructor (called when the object is first created)
    def __init__(self, parent):
        Tkinter.Tk.__init__(self, parent)
        self.parent = parent
        self.protocol('WM_DELETE_WINDOW', self.OnExit) # Call the OnExit function when user closes the dialog
        self.Initialise()

    # Initialise the dialog
    def Initialise(self):
        global filePath

        # Setup our dialog components
        self.title('PiWars Timer')
        self.grid()

        self.scrLists = Tkinter.Scrollbar(self, orient = Tkinter.VERTICAL)
        self.scrLists.grid(column = 5, row = 1, columnspan = 1, rowspan = 4, sticky = 'NSEW')
        self.scrLists.config(command = self.scrLists_scroll)

        self.lblResultName = Tkinter.Label(self, text = 'Robot')
        self.lblResultName['font'] = ('Arial', 20, 'bold')
        self.lblResultName.grid(column = 2, row = 0, columnspan = 1, rowspan = 1, sticky = 'NSEW')

        self.lstResultName = Tkinter.Listbox(self, selectmode = Tkinter.EXTENDED, exportselection = 0,
                                             yscrollcommand = self.scrLists.set)
        self.lstResultName.grid(column = 2, row = 1, columnspan = 1, rowspan = 4, sticky = 'NSEW')

        self.lblResultTime = Tkinter.Label(self, text = 'Time')
        self.lblResultTime['font'] = ('Arial', 20, 'bold')
        self.lblResultTime.grid(column = 3, row = 0, columnspan = 1, rowspan = 1, sticky = 'NSEW')

        self.lstResultTime = Tkinter.Listbox(self, selectmode = Tkinter.EXTENDED, exportselection = 0,
                                             yscrollcommand = self.scrLists.set)
        self.lstResultTime.grid(column = 3, row = 1, columnspan = 1, rowspan = 4, sticky = 'NSEW')

        self.lblResultSpeed = Tkinter.Label(self, text = 'Average speed')
        self.lblResultSpeed['font'] = ('Arial', 20, 'bold')
        self.lblResultSpeed.grid(column = 4, row = 0, columnspan = 1, rowspan = 1, sticky = 'NSEW')

        self.lstResultSpeed = Tkinter.Listbox(self, selectmode = Tkinter.EXTENDED, exportselection = 0,
                                             yscrollcommand = self.scrLists.set)
        self.lstResultSpeed.grid(column = 4, row = 1, columnspan = 1, rowspan = 4, sticky = 'NSEW')

        self.lblRobot = Tkinter.Label(self, text = 'Next Robot')
        self.lblRobot['font'] = ('Arial', 20, 'bold')
        self.lblRobot.grid(column = 0, row = 0, columnspan = 2, rowspan = 1, sticky = 'NSEW')

        self.lblPinStart = Tkinter.Label(self, text = 'Start')
        self.lblPinStart['font'] = ('Arial', 20, 'bold')
        self.lblPinStart['fg'] = '#FFFFFF'
        self.lblPinStart['bg'] = '#404040'
        self.lblPinStart.grid(column = 0, row = 1, columnspan = 1, rowspan = 1, sticky = 'NSEW')

        self.lblPinFinish = Tkinter.Label(self, text = 'Finish')
        self.lblPinFinish['font'] = ('Arial', 20, 'bold')
        self.lblPinFinish['fg'] = '#FFFFFF'
        self.lblPinFinish['bg'] = '#404040'
        self.lblPinFinish.grid(column = 1, row = 1, columnspan = 1, rowspan = 1, sticky = 'NSEW')
    
        self.lblRobotName = Tkinter.Label(self, text = 'Name')
        self.lblRobotName['font'] = ('Arial', 20, '')
        self.lblRobotName.grid(column = 0, row = 2, columnspan = 2, rowspan = 1, sticky = 'SEW')
        
        self.txtRobotName = Tkinter.Entry(self)
        self.txtRobotName['font'] = ('Arial', 20, '')
        self.txtRobotName.grid(column = 0, row = 3, columnspan = 2, rowspan = 1, sticky = 'NSEW')

        self.butGo = Tkinter.Button(self, text = 'GO!', command = self.butGo_click)
        self.butGo['font'] = ('Arial', 20, 'bold')
        self.butGo['bg'] = '#444444'
        self.butGo['activebackground'] = '#004400'
        self.butGo.grid(column = 0, row = 4, columnspan = 2, rowspan = 1, sticky = 'NSEW')

        self.lblLastTime = Tkinter.Label(self, text = 'Set name and press GO')
        self.lblLastTime['font'] = ('Arial', 20, 'bold')
        self.lblLastTime['bg'] = '#000000'
        self.lblLastTime['fg'] = '#FFFFFF'
        self.lblLastTime.grid(column = 0, row = 5, columnspan = 6, rowspan = 1, sticky = 'NSEW')
        
        # Set the grid scaling
        self.grid_columnconfigure(0, weight = 1)
        self.grid_columnconfigure(1, weight = 1)
        self.grid_columnconfigure(2, weight = 10)
        self.grid_columnconfigure(3, weight = 10)
        self.grid_columnconfigure(4, weight = 10)
        self.grid_columnconfigure(5, weight = 1)
        self.grid_rowconfigure(0, weight = 1)
        self.grid_rowconfigure(1, weight = 1)
        self.grid_rowconfigure(2, weight = 2)
        self.grid_rowconfigure(3, weight = 2)
        self.grid_rowconfigure(4, weight = 4)
        self.grid_rowconfigure(5, weight = 2)

        # Set the size of the dialog
        self.resizable(True, True)
        self.geometry('800x600')

        # Set initial state
        self.selectedName = None
        self.selectedTime = None
        self.runState = STATE_DONE

        # Place a file header
        fileOut = open(filePath, 'a')
        now = time.localtime()
        fileOut.write('=== %04d/%02d/%02d %02d:%02d:%02d ===\n' % (
            now.tm_year, now.tm_mon, now.tm_mday, now.tm_hour, now.tm_min, now.tm_sec))
        fileOut.close()

        # Start polling
        self.poll()

    # Polling function
    def poll(self):
        global pi
        
        # Check for list selection
        selectedName  = self.lstResultName.curselection()
        selectedTime  = self.lstResultTime.curselection()
        selectedSpeed = self.lstResultSpeed.curselection()
        if selectedName != self.selectedName:
            # Name selection updated, reflect in others
            self.selectedName = selectedName
            self.lstResultTime.select_clear(0, self.lstResultTime.size() - 1)
            self.lstResultSpeed.select_clear(0, self.lstResultTime.size() - 1)
            for index in selectedName:
                self.lstResultTime.select_set(int(index))
                self.lstResultSpeed.select_set(int(index))
            self.selectedTime = self.lstResultTime.curselection()
            self.selectedSpeed = self.lstResultSpeed.curselection()
        elif selectedTime != self.selectedTime:
            # Time selection updated, reflect in others
            self.selectedTime = selectedTime
            self.lstResultName.select_clear(0, self.lstResultName.size() - 1)
            self.lstResultSpeed.select_clear(0, self.lstResultTime.size() - 1)
            for index in selectedTime:
                self.lstResultName.select_set(int(index))
                self.lstResultSpeed.select_set(int(index))
            self.selectedName = self.lstResultName.curselection()
            self.selectedSpeed = self.lstResultSpeed.curselection()
        elif selectedSpeed != self.selectedSpeed:
            # Speed selection updated, reflect in others
            self.selectedSpeed = selectedSpeed
            self.lstResultName.select_clear(0, self.lstResultName.size() - 1)
            self.lstResultTime.select_clear(0, self.lstResultTime.size() - 1)
            for index in selectedSpeed:
                self.lstResultName.select_set(int(index))
                self.lstResultTime.select_set(int(index))
            self.selectedName = self.lstResultName.curselection()
            self.selectedTime = self.lstResultTime.curselection()

        # Update the robot running state
        if self.runState == STATE_DONE:
            # Waiting for the GO button
            pass
        elif self.runState == STATE_GO:
            # Go button has been pressed
            pass
        elif self.runState == STATE_RUNNING:
            # First sensor was tripped
            self.SetRobotRunning()
        elif self.runState == STATE_FINISHED:
            # Second sensor was tripped
            time = self.endTime - self.startTime
            self.SetLatestTime(self.robotName, time)
            self.runState = STATE_DONE
        else:
            # Unexpected state code
            self.lblLastTime['text'] = 'Unexpected state %d' % (self.runState)
            self.lblLastTime['bg'] = '#000000'
            self.lblLastTime['fg'] = '#FFFFFF'
            self.runState = STATE_DONE

        # Read the pin states
        start  = pi.read(SENSOR_START)
        finish = pi.read(SENSOR_FINISH)

        # Set the GUI status for start
        if start == 0:
            self.lblPinStart['bg'] = '#008000'
        elif start == 1:
            self.lblPinStart['bg'] = '#800000'
        else:
            self.lblPinStart['bg'] = '#000080'

        # Set the GUI status for finish
        if finish == 0:
            self.lblPinFinish['bg'] = '#008000'
        elif finish == 1:
            self.lblPinFinish['bg'] = '#800000'
        else:
            self.lblPinFinish['bg'] = '#000080'

        # Prime the next poll
        #self.after(1000, self.poll)
        self.after(20, self.poll)

    # Add a new time to the screen
    def SetLatestTime(self, name, finalTime):
        global filePath
        averageSpeed = (sensorDistance / finalTime) * 3.6 # kph
        fileOut = open(filePath, 'a')
        fileOut.write('%-20s %01.3f s (%01.2f kph)\n' % (name, finalTime, averageSpeed))
        fileOut.close()
        self.lstResultName.insert(Tkinter.END, name)
        self.lstResultTime.insert(Tkinter.END, '%01.3f s' % (finalTime))
        self.lstResultSpeed.insert(Tkinter.END, '%01.2f kph' % (averageSpeed))
        self.lstResultName.yview_scroll(1, 'pages')
        self.lstResultTime.yview_scroll(1, 'pages')
        self.lstResultSpeed.yview_scroll(1, 'pages')
        self.lblLastTime['text'] = '%s finished in %01.3f s, averaged %01.2f kph' % (name, finalTime, averageSpeed)
        self.lblLastTime['bg'] = '#000000'
        self.lblLastTime['fg'] = '#FFFFFF'

    # Called when the GO button is pressed
    def butGo_click(self):
        # Arm the measurement
        self.startTime = None
        self.endTime = None
        self.runState = STATE_GO
        self.robotName = self.txtRobotName.get()
        # Set the dialog display
        self.lblLastTime['text'] = 'Ready for %s to start' % (self.robotName)
        self.lblLastTime['bg'] = '#008000'
        self.lblLastTime['fg'] = '#FFFFFF'

    # Called when the robot is running
    def SetRobotRunning(self):
        now = time.time()
        current = now - self.startTime
        self.lblLastTime['text'] = '%s has been running for %01.3f s...' % (self.robotName, current)
        self.lblLastTime['bg'] = '#800000'
        self.lblLastTime['fg'] = '#FFFFFF'

    # Called when the scroll bar is moved
    def scrLists_scroll(self, *args):
        # Pass the scrolling on to all list boxes
        apply(self.lstResultName.yview, args)
        apply(self.lstResultTime.yview, args)
        apply(self.lstResultSpeed.yview, args)

    # Called when the user closes the dialog
    def OnExit(self):
        # Release GPIO and end the program
        global pi
        global filePath
        fileOut = open(filePath, 'a')
        fileOut.write('\n')
        fileOut.close()
        pi.stop()       
        self.quit()
    
    # Called when the start sensor pin changes state
    def StartSensorEdge(self, gpio, level, tick):
        if self.runState == STATE_GO:
            # Waiting for start marker, set to running mode
            self.startTime = time.time()
            self.runState = STATE_RUNNING
    
    # Called when the finish sensor pin changes state
    def FinishSensorEdge(self, gpio, level, tick):
        if self.runState == STATE_RUNNING:
            # Waiting for finish marker, set to finished mode
            self.endTime = time.time()
            self.runState = STATE_FINISHED

# Setup the GUI and the callbacks
gui = PiWarsTimer_tk(None)
pi.set_mode(SENSOR_START, pigpio.INPUT)
pi.set_mode(SENSOR_FINISH, pigpio.INPUT)
pi.callback(SENSOR_START, pigpio.RISING_EDGE, gui.StartSensorEdge)
pi.callback(SENSOR_FINISH, pigpio.RISING_EDGE, gui.FinishSensorEdge)

# Hand control over to the GUI
gui.mainloop()