How to make a lie detector with Arduino

final lie detector example

Continuing with the proposals to create your own projects, this time I want to show you how create an interesting lie detector With which to leave all your guests with their mouths open thanks to its good operation. As the title of this post says, this time we are going to use a simple Arduino board that will serve as the controller for the entire project.

In this project, in addition to learning how these types of detectors work in depth, something that is still interesting, will help us to know how our body works and the different responses it can give depending on the situation in which you find yourself or, on the other hand, the emotions you suffer depending on the question that they can ask you.

How the lie detector works

Before you even start building your lie detector, it may be best to understand how it works. Thanks to this, it will surely be much easier for you to understand why the hardware is connected in a certain way and especially why the source code that makes everything work correctly is programmed that way. Then that part of customization will arrive that you will surely want to try for adapt and customize the project to all the needs you may have.

The idea on which this project is based is to provide a means with which to achieve measure the differences in the mood of each person. One of the peculiarities of lie detectors and on which they were based at first is that skin changes conductivity depending on many states how can be the mood we have at a certain time.

This difference in the conductivity of our skin is called Electrodermal activity. (There is a lot of information about it on the internet). Thanks to this property of the skin we will try, with the help of Arduino and specific software, to see all these changes that occur in the conductivity of the skin depending on our mood through the use of graphics.

To start working with our peculiar lie detector, as we usually see in the different tests, we could start by sitting any subject in front of our hardware, connecting the sensors and answering easy questions such as'as it is called?' or 'where you live?'. These questions They will serve as a baseline to know the state of mind of the subject we want to ask. Later we can ask different questions to detect if they are lying or not because they can get nervous, which will produce a change in the baseline.

Arduino Nano

List of parts that we will need to build our lie detector

To carry out all this project we will have to use a microcontroller to detect the differences and send the data to the computer. In turn, for our computer to receive the data from this microcontroller, it must be equipped with a serial communication chip which leads us to the conclusion that, for example, an Arduino Mini or an Adafruit in their cheaper versions does not work for us. This point is basic to carry out this project so, if instead of an Arduino Nano as we will use, we have another type of microcontroller at home, we can use it as long as it has an integrated serial communication chip.

Necessary electronic components

Necessary materials

Tools needed

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  • Cutter

wiring for lie detector

We started shaping our lie detector by wiring the entire project

As you can see in the image that is located just above these lines, wiring the whole project is much easier than you can imagine since basically you only have to perform six simple steps:

  • Connect a cable, be generous with its length, to the Arduino's analog pin
  • Connect the resistor to Ground and to the wire that we previously connected to the Arduino's analog pin
  • Connect a fairly long wire to the Arduino's 5 volt pin
  • Connect the anode (long leg of the led) of the green led to pin 2 and the cathode (short leg) to the ground
  • Connect the anode of the orange led to pin 3 and the cathode to ground
  • Connect the anode of the red led to pin 4 and the cathode to ground.

This is all the wiring you will need to have connected. In principle, it is enough to have it like this and located on some surface so that nothing moves. We can cover all of this later and give it a much more attractive view.

different types of graphs

Now is the time to develop and install all the software to our lie detector

Before even starting to develop anything, we must be clear that, both to program and to compile the entire project we will use the latest version of Arduino IDE. We will use this version since, in the latest releases, a monitor was integrated that allows us to see the data received in a very visual way thanks to a graph in real time instead of using the serial monitor, where this information appeared in the format text.

To run this monitor we just have to open the Arduino IDE, go to the tools menu and it should be located just below the serial monitor. Once we have all this configured, you just have to download the file that I leave you just below these lines, open it and upload it compiled to your board.



connection of the cables to the velcro of the fingers

We make the clips that will go on the fingers of the subject to be tested

Once we have the project practically complete, it is time to take another step and create the clips that will be responsible for detecting the conductivity that our skin presents at a specific time.

As you can see in the images that are scattered throughout this same post, the idea goes through stick a strip of aluminum foil to the bottom of the velcro strip. This must be done in the two pieces of velcro that we are going to use.

Once we have the strips ready, and as you can see in the image that is located just above these lines, it is time to connect to the aluminum foil the cable that we have connected to the analog pin of Arduino. We must do this step, exactly in the same way, with the other piece of velcro and the cable that we have connected to the Arduino current pin, to the 5 volt pin. Make sure the connections are strong and won't disconnect just by moving the velcro a little.

example box for lie detector

Manufacture of a box to store all our hardware

In this case we will bet on make a kind of box to store all the components of our lie detector in a very rudimentary but quite effective way. The idea is to create a small compartment to store the velcro rings. This, in turn, should contain three small holes so that the LEDs can be seen.

As you may be imagining, the material that we are going to use to make this kind of box is the cardboard that appears in the list of necessary materials. From the cardboard that we have, we will cut two rectangles of 15 x 3 centimeters, a rectangle of 15 x 5 centimeters, three rectangles of 4 x 3 centimeters, a rectangle of 9 x 5 centimeters and a rectangle of 6 x 5 centimeters.

Once all the rectangles have been cut, we will take the 15 x 5 cm one that will serve as the base. The two 15 x 3 and two 5 x 3 rectangles will be glued to the sides of the base. Now it's time to glue the third 5 x 3 rectangle to the base at 6 centimeters from the side.

At this point you should have a rectangle that is divided into two sides, one with a length of 6 centimeters and the other with a length of 9 centimeters.. The side with a length of 6 centimeters is where we are going to place the electronics while, on the other side, it is where the finger pads will be housed.

At this point we only have to cut 3 holes, the size of the LEDs, in the 6 x 5 cm rectangle, gluing them next to the 6 cm. It would only be left to stick, with adhesive tape, the short side of the 9 x 5 cm rectangle on the side farthest from the 9 cm side. This last step will serve as a kind of lid that will move up and down to store and reveal the finger pads..

Once we have installed all the components inside the box, if everything has gone well, we must have a small lie detector before us. As you are probably thinking, although its operation is very simple, the truth is that it is not very precise since most professional lie detectors have a large number of sensors, such as a heart rate monitor, to determine with much more certainty if a subject is lying or not.

Further information:  instructables

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