O cenário
Two laser beams across the road detect a vehicle; the start sensor triggers a 555 monostable, and if the stop sensor closes before the pulse ends, the vehicle exceeded the speed threshold and an alarm lamp lights.
O que há neste desenho
Entenda as decisões por trás dele.
01
Use a 555 monostable to create a fixed time window
02
Model optical sensors as pushbutton switches for schematic clarity
03
Drive an alarm lamp with a BJT switch gated by the stop sensor
Reuse for any two-point speed gate or presence timer where a fixed detection window and threshold comparison are needed.