The scenario
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.
What is in this drawing
Read the decisions behind it.
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.
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