# How does a speed camera work?

Have you ever imagined how speed cameras work? What is the difference for speed meters? How does that accurate measurement of the speed that the vehicle passes through the highway happen? Equipment that is seen by many people as a villain, in fact, is an excellent tool to ensure the safety of many people. In this article, we will present to you all the information that will answer these curiosities, come on guys!

## Speed ​​camera – What is it?

There are several ways to measure the speed of a vehicle on a highway, one of which is through the speed camera, but despite being the most widely used, it is not the only one. People usually call everything radar, but radar is that mobile device that emits an electromagnetic wave, capturing its reflection and calculating the speed, as shown in the image below.

Do you know what the difference is from mobile radar to fixed speed gauges?

## Speed ​​meter – How does it work?

Speed ​​meters are called fixed speed cameras! They are those that use sensors installed on the asphalt. These sensors are called inductive loops and if you look closely, you can see some lines on the ground near these radars, as shown in the image below.

How does the speed meter calculate the speed that the car goes through the highway?

Most fixed speed cameras have 2 or 3 inductive loops, which are used to calculate and check the vehicle speed calculation. When a vehicle that is basically a metallic body passes through each inductive loop, it causes a disturbance in the magnetic field generated by each of the sensors. This disturbance is processed by software that can detect the time the vehicle has spent from one inductive loop to the other.

The calculation takes place as follows, as the distance between the sensors on the ground is fixed, it is very easy to calculate the speed of the vehicle using the formula: speed is equal to the distance divided by time! If the speed is above that allowed for that type of vehicle, a command is triggered to capture the image of the offender.

You probably don’t know, but there are several types of sensors and some are so sensitive that they can even detect the speed of a bicycle! They are generally more specific, detecting and differentiating trucks, cars, and motorcycles. This specification is what makes it possible for a detector to find cars from 80 km / h and heavy vehicles from 60 km / h, or even to detect whether a car is invading the bus lane.

See with a radar differentiate the type of vehicle that passes through the sensor!

In the following video, it is possible to see in practice how this disturbance detected by the sensors works. In the test performed, a photocell was covered leaving only two holes for the passage of light, that is, when the trolley passes over each hole, it blocks the light for an instant and causes a variation in the photocell output voltage. Therefore, the only difference is that instead of using an inductive loop, the test design carried out using a photocell that identified the variation in luminosity caused by the passage of the vehicle.

## How was the speed calculated in the test?

The speed meter in this test with the photocell used an Arduino and some shields without having to solder any components, that is, all the work was done only on the embedded software. The calculation happened in the same way that speed detectors do in real traffic. The distance between the two holes in the photocell is fixed. So, it was up to the software to just divide this distance by the measured time, resulting in the cart speed!

In the video description, you will find the link to download the software, the list of materials and the entire scheme used in the test performed with the photocell. We have reached the end of this article and if you have any questions, leave them in the comments and we will be happy to answer them.