## measuring linear velocity of a toy car

I want to measure the linear velocity of a toy car.. i had a thought over it..
i m thinking of using a optical mouse to do so , i need to process the usb output , how shud i do it ?.. and can there be any other cheap way of doing it..?
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 You could do it accurately and cheaply using 2 LEDs, 2 Phototransistors, a dual Op-amp configured as 2 comparators and a 3.5mm mini jack and a bit of audio cable to go into your computer's Audio In. Point an LED at a Phototransistor at the part of the car's run where you want the test to start and put the other one a little way ahead of it. Set the car running and use a sound recorder to sample the clicks made by the comparators as they trigger at the breaking and remaking of each of the LED beams. Look for the start of each event and record the time. Then look for the end of each event and record the times as accurately as you can. Add the times together (front of car goes past each LED, back of car goes past each LED) and divide by two to get the average. Measure the distance between the LEDs as accurately as you can. The linear velocity of the car is the distance travelled divided by the time taken. Total cost - less than 5 dollars. Have fun.
 i basically want to measure its speed with a independent system mounted on the car.. i want to get the velocity at every instant which is required for further processing of my algorithm... so using the led system every time wont do..

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## measuring linear velocity of a toy car

What ever happened to the way that we used to do it, with a stopwatch and a ruler?
 i was thinking of using a GPS module....but i need some other methods as GPS is costly