Introduction: Wearable Technology Rapid Prototyping Band 2.0
This band builds off of an original prototype I designed in 2014. The new band is extremely modular and allows for several different sensors and feedback components to be interchanged using snaps. The prototyping patch is small enough to fit on a female forearm and comes with adjustable elastic bands so that it can be placed anywhere on the body. The entire kit can be seen above, but this set of instructions will focus only on the main patch shown in the 2nd picture.
What can this patch work with?
- Microcontroller: SparkFun ESP8266 Thing
- Adafruit Neopixels
- Vibrating Disk Motors
I decided to work with the SparkFun Thing because it's easy to use and sends data to/from the computer wirelessly. I use MAX/MSP a lot, and the SparkFun Thing works great with it. You can use any microcontroller you want, but you'll need to modify the schematic accordingly.
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Step 1: Make a Paper Prototype and Cut Out the Base Fabric
Make Paper Prototype
Even if you are building this exactly as I did, I still recommend drafting it out on paper first. It's very useful to have a quick, non-digital reference as you're building. To do this, trace the components on the paper and draw out your connections. As you can see in the image the connections cannot cross. This patch uses conductive thread, which is like using exposed wire.
NOTE: The schematic above shows LED IN going to D5. I had to modify the final design so that LED IN goes to D0 instead. More about this can be found in STEP #3.
Cut Base Fabric
Once you have your paper prototype, you can use it to trace and cut out your base piece of neoprene fabric. My base piece is 7" x 4". This is much smaller than my original patch, which was 9" x 5". (see visual comparison above.) The larger patch was much easier to build, but it was difficult to wear on all parts of the body, particularly calves and forearms. Since most people want to prototype for distal ends of the body, I revamped the patch to make it more compact. This made it compatible for smaller, narrower body parts. If you are new to using a sewing machine and working with textiles, I recommend working with a bigger base patch at first. This will give you more room for error.
Step 2: Place the Base Circles
This step is optional, but I think it makes the patch look a little more playful and it's much easier to visually parse out what goes where. I find this visual layout incredibly useful if you're planning to use this band with students. It ensures users can identify which snaps belong to individual sensor/feedback components.
- Trace and cut out 4 circles. I used the photon breakout board for the microcontroller circle and random circular objects around the house for the rest.
- Trace and cut out 2 long ovals for the LED and disk motor snaps. I rounded the edges to maintain a similar aesthetic.
- Seal your edges. If you used cotton fabric like me, you'll need to make sure your fabric doesn't fray. For this, I use Fray Check. Line the edges of all your patterns and let dry.
- Once your fabric is dry, trace and cut stitch witch to cover all the edges of your fabric. You'll have to get a little creative here, as most of the shapes are wider than the stitch witch tape.
- Carefully lay all of the components onto your base patch and iron them on. Make sure to place a piece of fabric between your components and the iron. I used an old t-shirt. If you're not familiar with using stitch witch, just follow the instructions on the box. Remember, be careful when you lay everything down. You have lot of small components, and it's easy for them to move around in the process.
Once you're done, you should have a nice visual layout for the rest of your work.
Step 3: Solder Snaps and Modify the Breakout Board
Before you move on with the base patch, you'll need to solder snaps onto your microcontroller, sensors, and feedback components. Wearable sensors are pretty easy because the I/Os are intentionally spread out. If you're planning to use sensors that are not designated as "wearable," you'll have to get a little creative. Most sensors come with solder points for male leads. I recommend soldering the male leads in and bending them outward like a fan. This gives some space for snaps. Look at the absolute orientation sensor and the gain sensor as examples.
Modify Photon Breakout Board
To use the SparkFun Thing ESP8266 for this wearable application, I had to get creative. There is not yet a wearable breakout board for this mircocontroller, so I modified the Photon breakout board to fit my needs. The SparkFun Thing has 20 pins and the Photon has 24. I placed the SparkFun Thing in the center of the Photon breakout board, leaving an extra female input port on each side. You'll also notice that the Photon is narrower than the Sparkfun Thing, which means the SparkFun thing will not fit without modification. To make it work, do the following:
- Prepare your SparkFun Thing by soldering the male pins onto your board.
- Gently bend the female ports on the breakout board out with needle nose pliers.
- Place one side of the male pins on the SparkFun Thing into one side of the breakout board, hold the female ports with your needle nose pliers to stabilize, and gently press on the microcontroller to bend the pins in.
- Repeat step 3 with the other side.
You'll need to solder snaps onto the following breakoutboard I/Os (see image above). Make sure you use the male snap end, not the female side. This will make future steps much easier:
Snip Male Lead for Pin 5 on the Sparkfun Thing
You'll need to cut off the male lead connected to PIN 5. The Photon breakout board connects both of the Ground pins, so unless you sever the connection, the Thing's PIN 5 is technically connected to the Thing's Ground. This is why I mentioned the modification in Step #1.
Step 4: Make Templates for Sensors and Microcontrollers and Sew Conductive Thread
Make a Template
Once you've soldered male snaps to all of the sensors and the Sparkfun Thing, you'll use these to make templates. Pierce the male leads through paper, and then use the holes to mark where you'll sew your female snaps. This will prepare you for sewing.
For your feedback input locations, spread 3 snaps out equally. You'll make a custom connectors for your LEDs and motors, so there's no need to make templates. Mark by hand.
Sew Conductive Thread
Once you've marked all of the snap locations, machine sew the conductive thread between each major connection point. If a single line runs through multiple points, you can sew through middle points. Make sure you leave enough thread at the end of each line to hand sew the snaps down. Hand sew the snaps using embroidery stitch techniques. More about this is in Step 4 of my previous armband instructable.
Step 5: Make a Battery Pocket and Sew Down the Voltage Booster
Make a Battery Pocket
You'll need stretch fabric for this. Trace the battery and cut a rectangle slightly bigger. Machine sew this down close to the edge. Leave a small hole for the JST connector/cable. Sew "shoulders" at the bottom so the battery doesn't fall out.
Sew on the Voltage Booster
Hand sew the voltage booster down using available holes and the standard USB connector. NOTE: You only need the voltage booster if you are planning to accommodate haptics in your design. If you don't want to use haptics, then this piece is not necessary.
Step 6: Make Connectors for LEDs and Motors
As a reminder, all feedback connects to the long patches placed directly above and below the microcontroller. The top patch (orange and teal) is for LEDs, and the bottom patch (black and white diamonds) is for motors.
To connect the motors and LEDs, I went with a modular system that allows wearers to use variable length jumper cables to connect the band to the feedback components. This allows wearers to create various distances between the band and the feedback.
Solder snaps to the end of three wires, braid until the orientation matches your needs, and solder male leads to the other side. I use shrink tubing to hold the braids in place.
NOTE: I have three output snaps for my motors because I've been playing around with the neopixel chip to make independently addressable motors. If you only want to turn motors on and off, you can get rid of the power line and use your digital output and ground. (i.e. you'd use two rather than three outputs) You can also use this 3-output location to run more LEDs if you're not interested in haptics. If you want to fade the motors in and out, you'll need to share with the variable resistor patch circle (gray). The Sparkfun Thing only comes with one analog pin, and in this design I've dedicated it to variable resistor sensors.
The process for making connectors is almost exactly the same, but you won't have braid the wires. The orientation of the leads on the patch matches the orientation of the leads on the Neopixel LEDs.
Step 7: Make a Special Jumper Cable for Variable Resistors.
I built this so that I could use any variable resistor with the band. Snap off three male leads and bend one side to match the snap setup for variable resistors (in this image it's the circle with green zig-zags). Solder the snaps on one side and jumper cable on the other. Insert the resistor as shown.
Step 8: Sew on the Adjustable Hardware and Make Straps
The final step in making this band is adding the adjustable hardware and elastic straps that make it...wearable. You can follow my model or create your own. For this I used two plastic loops and two adjustable clamps. I don't have "official" names for these pieces because I picked them up from a local upholstery store. You can probably find similar parts online.
Sew on loops and clamps
For this, I used elastic to connect the hardware pieces to the band. You can use any other fabric, but I like that the elastic on the band matches the elastic I used to make the straps. Elastic is also much easier to work with if you want to machine sew the loops and clamps down.
Measure a piece of elastic long enough to loop through your hardware piece and comfortably connect it to the band. Cut and seal the edges with fabric glue. Elastic frays easily so don't forget to seal the ends. Thread your loop or clamp and lay the elastic ends on either side of the band's neoprene so the elastic is pinching the band. Make sure you're not covering any of your conductive thread lines. Machine sew the elastic to your band.
NOTE: I used these specific clamps to make adjustment easy. All wearers have to do is thread the elastic through and clamp down. Most adjustable fasteners require wearers to thread more than once (as in the hardware used on my LED strands). Since the band is taken on and off most often, I recommend using these clamps for added ease.
Make variable length elastic straps
Your final step is to make your straps. As you can see, I made several straps to accommodate various body parts and body types. I strongly recommend making several so that the band can be used in multiple ways. In hindsight, I would also recommend color coding your various length bands so that it's easy to tell them apart. I learned this after using them in my first class.
Cut your length and machine sew velcro to one side. The two sides of the velcro should be side-by-side. This velcro side will be threaded through the loop and secured down. The other side of your strap will be threaded through the clamp for adjustment.
Step 9: Wear!
This is it. Now your band is ready to wear. Good luck and happy prototyping!