상황
Two infrared beam break sensors are placed a known distance apart across a highway lane. A 555 timer measures the time between the first and second beam interruptions and lights an LED while the vehicle travels between them.
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01
Use two IR LED/photodiode pairs as start/stop sensors
02
Configure the 555 in monostable mode with the second sensor resetting the IC to stop timing
Reuse this netlist when you need a low-cost analog vehicle speed sensing front end, such as in highway monitoring, traffic counting, or speed warning displays.