Planet Arduino

Want to know if someone is telling you the truth? Well, unfortunately Juan Gg’s “USB Polygraph” isn’t a professional product and won’t actually give you an answer. However, it is a neat exploration into biometrics that incorporates Arduino, some sensors, and data visualization.

The DIY lie detector does measure one’s galvanic skin response, pulse, and breathing, so it’s an interesting way to observe “suspects” when questioned. Perhaps one could even use it to monitor a person’s vitals when performing various physical activities.

The device collects sensor readings via an Arduino Uno. These are then passed along to a nearby computer over serial, which graphs everything using a custom Python program. 

If you’d like to make your own, code and mechanical files are available on GitHub!

This is a USB Polygraph, which I designed and built as a classroom project on June 2018. The hardware side is pretty simple, an Arduino UNO collects data from some sensors and sends it via serial. On the computer, a Python program takes that data and not only graphs it, but it also allows the user to save it, manages questions and adds question and answer markers to the graphs so results can later be inspected. All results are saved in .txt files.

Some dogs have no sense of self-preservation. Given the opportunity, they will eat until they’re sick. It’s up to us humans to both feed them and remember doing it so they aren’t accidentally overfed. In a busy household with young children, the tricky part is the remembering.

[Bryan]’s family feeds their dog Chloe once a day, in the mornings. She was a rescue who spent a few years scrounging for meals on the street, so some part of her is always interested in finding food, even if she just ate. Each morning, the flurry of activity throughout the house is compounded by Chloe’s repeated requests for food, so [Bryan] got his kids involved and built a simple circuit that lets everyone know—at a glance—whether Chloe was fed.

Chloe’s kibble is kept in a touch-top wastebasket that flips open at the press of a button. [Bryan]’s dog-fed detector uses a reed switch and an Arduino clone to detect when the lid is opened. When the reed switch goes, low, the Arduino lights up an LED. The light stays on for two hours and then shuts off automatically to get ready for the next day. You don’t have to beg for a demo video, because it’s waiting for you after the break.

Since Chloe devours a bowl of food in about two minutes flat, maybe the next project for [Bryan]’s family could teach her to slow down a bit.

Hard as it is to imagine, lie detectors have been sold as children’s toys for a number of years. A simple battery-operated device clipped to your fingers and would show the conductivity of your skin. The concept — which is probably not very reliable — observers that lying causes you to imperceptibly sweat which causes a sudden increase in your skin’s conductivity. These cheap toys would have a meter and you’d note the meter deflection to determine if the subject was lying.

You can debate the amusement value of interrogating your friends, perhaps, but they were pretty common and still exist (including some that shock you if they detect you are lying). Seventeen-year-old [BuildIt] has his own modern take on this classic device using — what else? — an Arduino. You can see a video of the device below.

Of interest is how he used the latest version of the Arduino IDE to visualize the data graphically (see right). This is easier than interpreting a bunch of numbers scrolling by on the serial terminal or having to import the data into a spreadsheet. You can find the graph under the Tools menu listed as Serial Plotter.

You don’t need a lot of external parts for this project, although the finger clips and the cardboard box will take a little mechanical skill to complete.

We’ve looked at galvanic skin response and other biosignal processing before. You can do a lot more if you build a little more hardware.