Hacking Touch Screens to Count Pulses

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.

ESP32 Display is Worth a Thousand Words

The ESP32 is the successor to the wildly popular ESP8266. There seems to be no end to what the chips can do. However, despite all the wireless communication capabilities, the module doesn’t have a display. [G6EJD] wanted to connect an ILI9341 TFT display and he put the code and information on GitHub. You can also see a video of his work, below.

Since the display uses a serial interface, there isn’t much wiring required. The Adafruit GFX library does the heavy lifting, utilizing the SPI library for the actual communications. The first demo shown on the hardware can pull weather data decoded. If you want more details on the display’s operation, check out [G6EJD’s] YouTube channel and you’ll find other videos that go into more detail.

We’ve seen these displays married to an ESP8266 with an integrated PCB, too. There’s a choice of libraries, and perhaps we’ll see a similar range of choice for the ESP32.

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Helix Display Brings Snake Into Three Dimensions

Any time anyone finds a cool way to display in 3D — is there an uncool way? — we’re on board. Instructables user [Gelstronic]’s method involves an array of spinning props to play the game Snake in 3D.

The helix display consists of twelve props, precisely spaced and angled using 3D-printed parts, each with twelve individually addressable LEDs. Four control groups of 36 LEDs are controlled by the P8XBlade2 propeller microcontroller, and the resultant 17280 voxels per rotation are plenty to produce an identifiable image.

In order to power the LEDs, [Gelstronic] used wireless charging coils normally used for cell phones, transferring 10 W of power to the helix array.  A brushless motor keeps things spinning, while an Arduino controls speed and position via an encoder. All the links to the code used are found on the project page, but we have the video of the display in action is after the break.

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Hackaday Prize Entry: Safety Glasses Are Also Hands-Free Multimeter

It seems like the multimeter is never easy to see during a project. Whether it’s troubleshooting a vehicle’s electrical system and awkwardly balancing the meter on some vacuum lines and the intake manifold, or installing a new solar panel and hoping the meter doesn’t fall on the ground while the leads are in both hands, it seems like there’s never a good way to see the meter while actually using it. Some meters have a small magnet and strap that can be used to hang them temporarily, but this will only get you so far.

[Alain Mauer]’s entry into the Hackaday Prize looks to solve this glaring problem. Using a heads-up Bluetooth display mounted to a pair of safety glasses, a multimeter can be connected to the device in order to display its information directly to its user. Based on his original idea which used a normal pair of prescription glasses as its foundation, [Alain]’s goal is to reduce safety hazards that might arise when using a multimeter in an awkward or dangerous manner that might not otherwise be possible.

The device uses an Arduino Pro Micro to connect to the multimeter and drive the display. [Alain] notes that the real challenge is with the optical system, however. Either way though, this would be a welcome addition to any lab, workspace, or electrician’s toolbox. Be sure to check out the video of it in action after the break.

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E-ink Display Driven DIY

E-ink displays are awesome. Humans spent centuries reading non-backlit devices, and frankly it’s a lot easier on the eyes. But have you looked into driving one of these critters yourself? It’s a nightmare. So chapeau! to [Julien] for his FPGA-based implementation that not only uses our favorite open-source FPGA toolchain, and serves as an open reference implementation for anyone else who’s interested.

Getting just black and white on an E-ink display is relatively easy — just hit the ink pixels with the same signal over and over until they give up. Greyscale is made by applying much more nuanced voltages because the pixels are somewhat state-dependent. If the desired endpoint is a 50% grey, for instance, you’d hit it with a different pulse train if the pixel were now white versus if it were now black. (Ever notice that your e-book screen periodically does a white-black flash? It’s resetting all the pixels to a known state.) And that’s not even taking into account the hassles with the various crazy voltages that E-ink displays require, which [Julien] wisely handed off to a dedicated chip.

In the end, the device has to make 20-50 passes through the screen for one user-visible refresh. [Julien] found that the usual microcontrollers just weren’t capable of the speed that he wanted, hence the FPGA and custom waveform tables. We’ve seen E-ink hacks before, and [Julien] is standing on the shoulders of giants, most notably those of [Petteri Aimonen] and [Sprite_tm]. [Julien]’s hack has the fastest updates we’ve ever seen.

We still can’t wait for the day that there is a general-purpose E-ink driver chip out there for pennies, because nearly every project we make with a backlit display would look better, and chew through the batteries slower, with E-ink. In the meantime, [Julien]’s FPGA implementation is pretty close, and it’s fully open.

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Star Trek Desktop Viewer In The Palm Of Your Hand!

There’s building small computers — like the Raspberry Pi — and then there’s building small computers — like this Desktop Viewer from Star Trek.

[Monta Elkins] is using a Beetle for this project; it’s an Arduino clone, hosting the ATMega32U4 microcontroller, with a unique feature that allows you to twist connecting wires to secure them to the board. Instead, [Elkins] went with the logical choice of soldering them. For a display, he used a SPI serial OLED 128 x 64 monochrome screen which he has cycling through a number of iconic Star Trek TOS symbols and animations. The images were converted into PROGMEM  — which gets loaded into flash memory — before finally being uploaded to the Beetle.

Following some fine 3D print work in ABS plastic which rendered the Desktop Viewer’s case, [Elkins] used acetone to solvent-weld the pieces together and applied a quick coat of paint to finish it off. This little replica would make a great desktop gadget as it requires a micro-USB to power the device.

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An Ugly but Functional Pi Laptop

It’s got a face only its mother could love. Or a Hackaday writer, since this ugly e-waste laptop proudly sports a Jolly Wrencher on its back.

All joking aside, this is a great example of doing what you can with what you’ve got. [starhawk] is limited on funds, and a regular laptop is beyond his means. But being light in the wallet is no reason to go without when you can scrounge parts from friends and family. The base of the laptop is a mini USB keyboard, with the top formed mainly by a 7″ HDMI panel. The back of the display is adorned with a Raspberry Pi 3, a USB hub, a little sound dongle, and the aforementioned Jolly Wrencher. The whole thing is powered by a cast-off power supply brick — no exploding batteries to worry about!

Other Pi-based laptops we’ve covered may be sleeker, but we’ve got to admit that [starhawk]’s keyboard is probably the better choice for working on the next great American novel. And a Linux laptop for next to nothing? That’s a win in our book.