Arduino Polygraph Shows How It’s Done

December 25, 2019 by Donald Papp 9 Comments

Sometimes, a project comes along that makes a good reference design for anyone doing similar work. In this particular case, it’s a DIY USB polygraph-like machine by [Juangg] using an Arduino and sensors on the hardware side, and a Python front end for data visualization. It’s even complete with 3D printed enclosure and sensor elements.

[Juangg] designed it to use three sensors: a pulse sensor, a breath sensor, and one to measure Galvanic Skin Response (GSR). The pulse sensor uses a piezo element pressed against a fingertip to detect changes in pressure resulting from blood flow. It can be picky about placement, but finding sweet spot can yield remarkably good readings. The breath sensor works on a similar principle but uses a 3D printed fixture to hold the sensor between a strap and the subject’s chest, so that breathing in and out can be detected. The GSR sensor is a voltage divider used to measure small changes in skin conductivity. How well does it all work? That depends on what one is looking to get out of it, but the documentation and design files are available from the project page and the GitHub repository if anyone wants a reference for similar work.

The polygraph may have a mixed reputation, but it makes a good project that demonstrates just how messy biometrics can be from an engineering perspective. And in case you missed it, here’s a reminder that Wonder Woman and the polygraph have much more in common than you might realize.

Laser Welding With A Tattoo Removal Gun

December 25, 2019 by Lewin Day 49 Comments

Dating as far back as the early 1960’s, researchers were zapping tattoo inks with laser light was an effective way to remove the markings from human skin. At the time it was prohibitively expensive. But the desire to have an undo-button for badge choices is strong, and thus the tattoo removal gun was born.

These days you can pick up one of these zappy, burn-y wonders for far less than a flagship cellphone put their high-power-output to alternative use. [Andrew] recently discovered that these devices can be readily repurposed into a laser welding tool with just a bit of work under the hood.

He first came across the technology via videos from [styropyro], whose work we’ve featured before. The tattoo removal gun features a YAG laser, which is pulsed to create a high power density. In initial testing, the pulses were too short and of too high intensity to effectively weld with; instead, the pulses simply cratered the metal.

After delving in further, [Andrew] discovered that by removing the Q-switch optical component, the pulses from the laser could be lengthened. This reduces the power density, and allows the tool to weld various materials even on its lower power settings. Success was found welding steel, titanium, and other materials, though attempts to weld copper and silver faced little success. Test pieces included razor blades and small screws, which could easily be welded with the tool. Results of the razor blade welding is spectacular, with a high-quality welding bead achieved by taping the laser to a CNC mill for precise movement.

It could prove to be a useful tool for those experimenting with complex projects involving bonding metals at very fine scales. If you’re pursuing something exotic yourself, we want to hear about it!