RC Lap Timer with an Infrared Gate

Racing friends is more fun with real numbers. When a car breaks the infrared beam, gpiozero triggers an event and the Pi records the lap time.

Mission steps

1. Mount the beam

   Place the emitter and receiver on opposite sides of the finish line, a few centimetres above the track.

2. Wire the receiver

   Receiver output to GPIO17 with the pull-up enabled, power from 3V3 or 5 V as the sensor requires (output must be 3.3 V safe).

3. Run the timer

   Each break starts a new lap; a minimum lap time ignores double triggers.

4. Show results

   Print laps to the OLED or serve a live leaderboard web page.

5. Race

   Add a start countdown with a buzzer and an LED tree.

Code

from gpiozero import Button
from signal import pause
import time

gate = Button(17, pull_up=True)
last, laps, MIN_LAP = None, [], 2.0

def crossed():
    global last
    now = time.monotonic()
    if last and now - last >= MIN_LAP:
        laps.append(now - last)
        print('Lap %d: %.3f s  best %.3f s' % (len(laps), laps[-1], min(laps)))
    if not last or now - last >= MIN_LAP:
        last = now

gate.when_pressed = crossed
pause()

Tip: test every script on the bench before installing it in a moving machine.

Questions