Hacking Touch Screens To Count Pulses

July 9, 2017 by Inderpreet Singh 5 Comments

Heart rate sensors available for DIY use employ photoplethysmography which illuminates the skin and measures changes in light absorption. These sensors are cheap, however, the circuitry required to interface them to other devices is not. [Petteri Hyvärinen] is successfully investigating the use of capacitive touchscreens for heart rate sensing among other applications.

The capacitive sensor layer on modern-day devices has a grid of elements to detect touch. Typically there is an interfacing IC that translates the detected touches into filtered digital numbers that can be used by higher level applications. [optisimon] first figured out a way to obtain the raw data from a touch screen. [Petteri Hyvärinen] takes the next step by using a Python script to detect time variations in the data obtained. The refresh rate of the FT5x06 interface is adequate and the data is sent via an Arduino in 35-second chunks to the PC over a UART. The variations in the signal are very small, however, by averaging and then using the autocorrelation function, the signal was positively identified as a pulse.

A number of applications could benefit from this technique if the result can be replicated on other devices. Older devices could possibly be recycled to become low-cost medical equipment at a fraction of the cost. There is also the IoT side of things where the heart-rate response to media such as news, social media and videos could be used to classify content.

Check out our take on the original hack for capacitive touch imaging as well as using a piezoelectric sensor for the same application.

Hackaday Prize Entry: Watching Out For Forest Fires

July 9, 2017 by John Baichtal 27 Comments

Hackaday Prize entrant [Danie Copnradie] lives in South Africa where wildfires are a major problem. Every year, humans and animals are killed, crops are destroyed, and property is lost. The FireBreakNet project aims to deploy wireless environmental sensors that alert farmers, park rangers, and emergency personnel when fires break out.

According to [Danie], firefighting services are underfunded in South Africa, with farmers and their employees having to do a lot of the work involved in firefighting with their own equipment. Having access to a network of early warning sensors would allow for faster response times, saving money and lives.

The goals of the project include a low price, easy deployment, low power consumption, physical ruggedness, and scalability. Currently, [Danie] is testing Adafruit Feather as well as Texas Instruments LaunchPad for the brains of each node, taking readings from CO2 and temperature sensors, optical air quality sensors as well as optical flame sensors.

Tweet The Power Of Lightning!

July 8, 2017 by James Hobson 15 Comments

How quickly would you say yes to being granted the power to control lightning? Ok, since that has hitherto been impossible, what about the lesser power of detecting and tweeting any nearby lightning strikes?

Tingling at the possibility of connecting with lightning’s awesome power in one shape or another, [Hexalyse] combined AMS’s lightning sensor chip with a Raspberry Pi and a whipped up a spot of Python code to tweet the approach of a potential storm. Trusting the chip to correctly calculate strike data, [Hexalyse]’s detector only tweets at five minute intervals — because nobody likes a spambot — but waits for at least five strikes in a given time frame before announcing that a storm’s-a-brewing. Each tweet announces lightning strike energy, distance from the chip, and number of strikes since the last update. If there haven’t been any nearby lightning strikes for an hour, the twitter feed announces the storm has passed.

It just so happened that as [Hexalyse] finished up their project, a thunderstorm bore down on their town of Toulouse, France putting their project to the test — to positive success. Check out the detector’s tweets (in French).

We recently featured another type of lightning detector that auto-deploys a lightning rod once a storm arrives!

Radar Sensors Put To The Test

May 24, 2017 by Al Williams 68 Comments

[Andreas Spiess] picked up a few inexpensive radar sensors. He decided to compare the devices and test them and–lucky for us–he collected his results in a video you can see below.

The questions he wanted to answer were:

Are they 3.3 V-compatible?
How much current do they draw?
How long to they show a detection?
How far away can they detect the motion of a typical adult?
What is the angle of detection?
Can they see through certain materials?
Can the devices coexist with other devices in the same area? What about WiFi networks?

Good list of questions, and if you want to know the answers, you should watch the video.

Continue reading “Radar Sensors Put To The Test” →

Precision Pressure In A Piston

May 9, 2017 by Brian Benchoff 26 Comments

[Scott] is building a DIY yeast reactor for his aquarium. What’s a yeast reactor? [Scott] wants to pump carbon dioxide into his aquarium so his aquatic plants grow more. He’s doing this with a gallon of sugary, yeasty water bubbling into a tank of plants and fish. In other words, [Scott] is doing this whole thing completely backward and utilizing the wrong waste product of the yeast metabolism.

However, along the way to pumping carbon dioxide into his aquarium, [Scott] created a very high precision pressure sensor. It’s based on a breakout board featuring the MS5611 air pressure sensor. This has a 24-bit ADC on board, which translates into one ten-thousandths of a pound per square inch of pressure.

To integrate this pressure sensor into the aquarium/unbrewery setup, [Scott] created a pressure meter out of a syringe. With the plunger end of this syringe encased in epoxy and the pointy end still able to accept needles, [Scott] is able to easily plug this sensor into his yeast reactor. The data from the sensor is accessible over I2C, and a simple circuit with an ATmega328 and a character LCD displays the current pressure in the syringe.

We’ve seen these high-resolution pressure sensors used in drones and rockets as altimeters before, but never as a pressure gauge. This, though, is a cheap and novel solution for measuring pressures between a vacuum and a bit over one atmosphere.

Continue reading “Precision Pressure In A Piston” →

Thermal Panorama One Pixel At A Time

May 2, 2017 by James Hobson 10 Comments

Inspiration can strike from the strangest places. Unearthing a forgotten Melexis MLX90614 thermopile from his ‘inbox,’ [Saulius Lukse] used it to build a panoramic thermal camera.

[Lukse] made use of an ATmega328 to control the thermal sensor, and used the project to test a pair of two rotary stage motors he designed for tilt and pan, with some slip rings to keep it in motion as it captures a scene. That said, taking a 720 x 360 panoramic image one pixel at a time takes over an hour, and compiling all that information into an intelligible picture is no small feat either. An occasional hiccup are dead pixels in the image, but those are quickly filled in by averaging the temperature of adjoining pixels.

The camera rig works — and it does turn out a nice picture — but [Lukse] says an upgraded infrared camera to captured larger images at a time and higher resolution would not be unwelcome.

Another clever use of a thermopile might take you the route of this thermal flashlight. if you don’t build your own thermal camera outright.

[Thanks for the tip, Imn!]

Fundamentals Of Fingerprint Scanning

April 27, 2017 by Al Williams 28 Comments

Like most (if not all) Hackaday readers, I like to know how the technology I use works. I’m always amazed, for example, how many otherwise smart people have no idea how the cellphone network works other than “it’s a radio.” So now that I have two phones with fingerprint scanners on them, I decided I needed to know more about what’s going on in there.

Sure, I assumed the sensor was capacitive (but maybe not, I found out). Plus we all know some super glue, scotch tape, and gummy bears are all you need to fake one out. However, that’s been known for about 15 years and we are still seeing phones and other devices rolling out with the same scanners. So for now, put aside the debate about whether we should be using fingerprint scanners. Let’s talk about how those sensors work.