Piezo Coax Cable


i have a project where i need to measure the speed of cars, on a one wide road, one lane wide.For this i want to use this cable ( Piezo Coax Cable ) , having two lines of this sensors separated a know distance and save the time when the car pass over each sensor would give me what i need to calculate the speed.

My question is : How do i interface this cable with arduino ? Maybe i need an amp or some kind of circuit to make it work like a switch? I have a Mega 2560 and i'm thinking using interrupts to detect when the car has passed over the sensor and record the time in millis.

is this viable ?

any suggestion would be appreciated

PD: Cable generates around 15 - 30 volts when pressed by foot


Piezos normally do have the voltage, but don't have the power to damage an input. They are like capacitors, so you do need a resistor to ground to keep any DC voltage at ground potential. Enter "knock sensor" in the search box on top of this page. Normally a 1megohm is used for that. You might have to find out if the cable outputs a positive pulse when pressed and a negative when released. You can do that by measuring the voltage with a DMM (2volt) and slowly press the cable. If the voltage goes positive when pressed, connect the 1megohm resistor to ground and work with a positive going interrupt pulse in your code. If negative going when pressed, connect the 1meg resistor to +5volt, and detect a negative going interrupt. Not a coder, but I think you have to use an interrupt with micros() for maximum speed resolution. Leo..

I would be concerned about its structure being damaged by by cars driving over it. None of the listed uses suggests that sort of physical stress.

A couple of cars may be ok but many cars are likely to tear it apart fairly quickly.