Thursday, March 2, 2017

Wearable comparison

Overview

Wearable electronics projects are incredibly popular. Adafruit lists 188 tutorials in their Wearables category, and there are many Arduino-compatible microcontroller boards aimed at wearable projects. Today we'll take a look at three of them (Gemma, LilyPad, and Flora) with a quick peek at a fourth (Adafruit's Circuit Playground).

Like most Arduino boards, the wearable boards emphasize simplicity and ease of use for specific functions. All three discussed below have the same round form factor and alternating outputs that can use alligator clips, conductive thread, or more traditional soldered connections. They don't offer the traditional GPIO outputs of the Arduino Uno, but instead supply a wearable-oriented platform. They also all use ATMega chips, the standard for Arduino.

Gemma

Image courtesy of WikiMedia under a Creative Commons Attribution-Share Alike 4.0 International license
The Gemma is the smallest (in terms of both size and resources) of our microcontroller boards. With a mere 8 kB of memory, more than a quarter of which is taken up by the bootloader, Gemma programs must be small indeed. Of course, with only three output pins and relatively low power there isn't much to control, so you don't really need enormous programs. Fortunately, you don't need complex programming to make cool stuff...

You connect to the board with a micro USB connector, like the Flora. The Gemma can be powered over USB or via the battery connector (off-white plastic in the image above) for maximum wearable portability. The Arduino IDE can connect and upload programs to the Gemma, making it easy to get started for those already familiar with the interface. The lack of serial support can be a problem when debugging sensors, but the Gemma isn't really aimed at those sensor-intensive projects.

The Gemma has two pulse width modulation (PWM) ports and one analog port. Pulse width modulation uses digital outputs that are either on or off (a binary state) to mimic analog outputs by varying the amount of time the signal is on. In practical wearable terms, the Gemma has three pins it can use for fading LEDs, for instance (in addition to its power pins).

The Gemma has been used in some pretty cool wearable projects. I think my favorite might be the Iron Man arc reactor project, but I'm an equally big fan of the pixel heart (and I'm really a sucker for anything Becky Stern does). The common thread for Gemma projects is that they're almost exclusively centered on LEDs, with one sensor or an additional board. The Gemma is a minimal (and cheap) entry point, leading to equally minimal projects.

LilyPad

The LilyPad is the Gemma's big sibling, with a few key differences. The LilyPad has many more output pins (14 digital, 6 analog), twice as much memory, and is nearly twice as wide across. It is also somewhat less user-friendly from the outset, because unlike the Gemma it doesn't support a USB connector. Instead, you need to connect over a serial connection.
Courtesy of SparkFun Electronics under a Creative Commons CC BY-NC-SA 3.0 license
Of course, the serial interface is preferable to some hackers working with a lot of sensors, as mentioned above. Personally, I have found serial connections to be vastly more intimidating for the new hacker.

Most interestingly, the LilyPad is washable. You read that right - you can hand wash your garment without removing the LilyPad (at your own risk). Obviously you have to remove the power supply, but being able to gently wash the garment with the board attached is a great boon to wearable projects. Clothing gets gross quickly, and it would be great if the project could last longer than a few wearings without requiring significant re-stitching.

Otherwise, the LilyPad offers similar capabilities to the Gemma. And like the Gemma, it has been used in many cool projects. SparkFun's Dungeons & Dragons dice roller gauntlet is pretty amazing, and is a good opportunity to learn both sewing and electronics.

Flora

The Flora is Adafruit's Arduino-compatible wearable development board. Adafruit also manufactures a line of compatible expansion boards, like a Bluetooth module. The Flora is quite a bit more powerful than either the Gemma or LilyPad, and is aimed at more advanced projects.

One of the major differences between the Flora and the Arduino boards is the availability of detailed technical information. While the Flora's schematics are available, they're nowhere near as readable as the straightforward tech specs provided for the Gemma and LilyPad. In addition, you need to use the Arduino IDE's board manager to add the Flora and make it compatible with the IDE. These slight usability hiccups highlight how much effort the Arduino team puts into making their boards an ideal starting point for people with minimal electronics experience.

Image courtesy of Becky Stern under a Creative Commons Attribution-ShareAlike 2.0 Generic license
It's not all bad, of course. The Flora's built-in power regulator means that it's nearly impossible to fry by plugging a battery in the wrong way, a significant risk with the Gemma. As has been the theme, it's also well-supported by great tutorials and projects!

The Flora does have one particularly killer feature compared to the Gemma and LilyPad: a built-in RGB Neopixel LED, beyond the four indicator LEDs. For rapid prototyping or basic projects, that makes it an all-in-one solution. Otherwise, it's much the same as the LilyPad, albeit with a slightly more updated processor. It's even washable!

Circuit Playground

My addition to the wearables list is Adafruit's Circuit Playground. I picked one of these up a few weeks ago, and I LOVE it. It's based on the Flora and has the same form factor, but includes a host of integrated sensors, LEDs, and switches for only $5 more. The board has an accelerometer with tap detection, a microphone, a speaker, a thermistor, a photoresistor, 10 RGB Neopixel LEDs, two push buttons, and a toggle switch. It is GREAT. I recommend it for prototyping any wearable project (though it's out of stock at the moment).

video

Enjoy this video of me, courtesy of me, being really excited after testing out some code on the Circuit Playground. It makes a really cool Star Trek communicator badge!

Which one should you use?

  • Gemma: Ideal for super low power projects, usually involving LEDs. Plan to add just one sensor, if any.
  • LilyPad: Great for washable projects or more complex circuits needing a variety of I/O pins. Get going right away with the Arduino IDE.
  • Flora: The onboard Neopixel LED is great for rapid prototyping, and it opens up the Adafruit ecosystem. Requires more setup.
  • Circuit Playground: Just pick this one, as long as you don't need to wash it. The onboard sensors and outputs mean you can take on many, many projects and it's incredibly easy to get up and running.

Conclusion

There are some great microcontroller boards for use in wearable projects. They vary somewhat in terms of resources available and community support, but as Arduino-compatible boards there's no shortage of cool projects to make including sensors, LEDs, and switches.

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