Hello guys and welcome to Mundo da Elétrica!
In today's video I will explain how does a speed meter works!
Let's get started!
There are several ways to measure the speed of a vehicle on a road.
The radar is one of them, but it's not the only way.
We usually call it radar, sparrow way. or other less friendly names, but the radar
itself is that mobile device that emits an electromagnetic wave and captures its reflection,
calculating the speed in this
Today I'll talk about another type of speed meter: fixed speed cameras!
Fixed speed cameras use sensors installed on the road, called inductive loops.
You already may have seen a few lines on the ground near these speed meters.
Usually a fixed radar is composed by 2 or 3 inductive loops, used to calculate and
validade the calculation of the vehicle speed.
When a vehicle, which is basically a metal body, goes 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 how long the vehicle spent
from one sensor to another!
As the distance between the sensors on the ground is fixed, it is easy to calculate the speed
of the vehicle using the formula speed = distance / time!
Then, if the speed is above the allowed for that type of vehicle, a command is issued
to capture the image of the vehicle.
Some sensors are so precise that they can even detect bikes!
And depending on their format they can be more specific and also detect the type of
vehicle, differentiating between trucks, cars and motorcycles!
This kind of differentiation is what makes possible issue a fine for cars over
80 km / h and for trucks on another range over 60 km / h ... or even detect that a car
is invading the bus lane.
I'll show now a speed meter which follows a principle very similar to this!
The difference is that instead of using an inductive loop our project uses
a photocell and identifies the change in brightness caused by the passage of the
vehicle!
We cover the photocell and left only two holes for the light to pass.
When our small car passes over each hole it blocks the light for a moment and causes
a variation in the output voltage of photocell!
Then it got more interesting! I am using a Keysight DSOX1102G
100Mhz Digital Oscilloscope.
This oscilloscope is very interesting for those who work with electronics and it is connected
directly to the output voltage of the photocell, which is an analog signal, that varies
continuously over time!
To make things easier, I turned on the digital multimeter function on the oscilloscope,
which in real time is showing the voltage as if it were a single multimeter. It is one of the many functions
of this oscilloscope.
We need to make the Arduino understand this signal so it can calculate the speed of the car!
Processors only understand digital signals and therefore we need a digital-analog converter
or ADC to digitize the voltage variation caused by the car!
I have here an Arduino Uno board connected to some shields sent to me by Circuitar.
Shields are expanding circuits for a project.
The advantage is that a shield comes ready to use and you do not need to worry
about the connection details, design and soldering of electronic components.
One of the shields sent by Circuitar is the analog to digital converter.
In this video's description you have a link with more details of this converter, which is
the main part of this project.
With it I can convert the analog variations in voltage to digital values and calculate
the time taken by the car to cover the distance between the holes.
Every time our little car passes through a hole, the Arduino software detects the point of least
voltage on the curve.
I connected the oscilloscope channel 2 to a digital Arduino pin and I pulse 58 00:03:53,870 --> 00:03:58,770 in this digital output each time the Arduino detects a valley in the voltage curve.
The sofware also calculates the time between two consecutive valleys.
The oscilloscope greatly facilitates the process, automatically measuring the time
between pulses, which of course is the same as measured by Arduino.
In the display shield connected to the Arduino you can also see the speed that was
calculated for the car.
And how the speed calculation was done?
Just as the speed traps do in real traffic.
The distance between the two holes in the photocell is fixed!
The software only divide this distance by the measured time and than it has the speed of the car!
That is it! We did a speed meter using some Arduino shields without having to weld
a single component. All the necessary work was done only
in the embedded software.
Ahh, and I put in the video's description the link you can use to download the sofware used here
and also the entire list of materials I used.
And as I studied a lot to make this video, I also made available in the the description
a link to the main source I used. It was the master's thesis of Régis
Eidi Nashimoto. Thank you Regis! Well ... that's is all folks! I hope you
enjoyed this video!
If you have any questions or suggestion, comment below!
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That is it folks and I see you on the next video!
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