SIMULATION FLOW
Distance reading -> valid? -> below 25 cm? -> STOP or FORWARD
                       | invalid
                       +---------------> STOP

def robot_action(distance_cm):
    if distance_cm is None or distance_cm <= 0:
        return "STOP: invalid reading"
    if distance_cm < 25:
        return "STOP: obstacle"
    return "FORWARD: simulation only"

for distance in [80, 42, 24, 12, None, 60]:
    print(distance, "->", robot_action(distance))

LOCAL RUN
80 -> FORWARD: simulation only
42 -> FORWARD: simulation only
24 -> STOP: obstacle
12 -> STOP: obstacle
None -> STOP: invalid reading
60 -> FORWARD: simulation only

This is a tiny simulated control example, not a physical robot test or a safety-certified controller. It shows how a missing reading should change behaviour instead of silently meaning “clear path.” A real build also needs stale-reading detection, braking-distance limits, a physical stop control and hardware testing.

NEXT EXPERIMENT
Add separate stop and resume thresholds so noisy readings near 25 cm do not make the simulated robot chatter between states.