Create your own screen accurate Hello Unicorn backpack from Altered Carbon that automatically lights up when you unzip and open it. Ever since I first watched the show I've been obsessed with this backpack, so I built one to bring to Denver Comic Con. I even found a Takeshi Kovacs cosplayer to model it for me! I also use it when I teach workshops on costume tech as an example of incorporating electronics into cosplay prop builds.
Don't know what the Hello Unicorn backpack is? Check out this reference: a video with lots of Hello Unicorn moments from the official Altered Carbon Facebook page.
How Does It Work?
The interior is lined with addressable LEDs set to a blueish hue (matching the show) that turn on when the backpack is open and turn off when it is closed again. The trigger mechanism is a small magnet and reed switch placed on either side of to center of the backpack that connect to an Arduino microcontroller.
You'll need some basic soldering, painting, and sewing skills to complete the project and basic experience uploading code and installing libraries in Arduino.
- SparkFun Pro Micro 5Vor equivalent microcontroller with micro USB connector
- ~2.25 meters of NeoPixel LED strips, I used these(you can sub a single color/non-addressable strand to save money or if you don't care about the blue hue matching the show exactly)
- Electrolytic capacitor - 1000uF/25V (optional, but helps with performance)
- USB power bank, I used this slim 5Ah lithium ion battery pack
- Micro USB cable (if not included with the power bank)
- Insulated reed switchthe plastic casing is more durable
- ~3-4 ft of stranded hookup wire (ribbon cable works great for this)
- Soldering iron and solder
I made a wishlist on SparkFun.com with most of the parts I used for this build (excluding soldering tools). Feel free to swap any of the parts in this list with compatible parts as needed for price and sourcing considerations.
- Pink hard shell backpack (I found one on Amazon with construction very similar to the one used in the show)
- Spray paint - white primer and pink slightly darker than the fabric of the backpack bring print outs with you to the store to find the perfect color
- Paint brushes large and small for fine detail
- Acrylic paints in red, yellow, orange, green, light blue/teal, dark blue, purple, light purple, white, and black
- Spray acrylic clear coat/sealer
- Masking tape
- Vinyl cutter and vinyl I used a Silhouette Cameo and 12x12 vinyl sheet
- Permanent marker and pencil
- Clear vinyl (I used less than 1/2 yard)
- Clear or pink thread and needle
- Exacto knife and/or small scissors
- Hot glue gun
- Pink fabric to match interior of backpack
- Thick black webbing (if you'd like to attach to the top of the backpack for screen accuracy)
- Small magnet (rare earth magnet works best)
- Sewing machine (optional)
- Small plastic bags (optional, for 'drugs' to fill the bag with)
Addipak 3ml unit dose containers, wax stick candy, or mini glow sticks (optional, for 'drugs' to fill the bag with)
- Arduino IDE - https://www.arduino.cc/en/Main/Software
- Pro Micro support for Arduino - https://learn.sparkfun.com/tutorials/pro-micro--fio-v3-hookup-guide
- Adafruit NeoPixel Library - install through the library manager in Arduino
Step 1: Prime and Mask Backpack
This is the most important step of the build - getting the backpack just right! First, we'll prime and paint the plastic shell of the backpack.
Don't forget to remove the thin plastic film coating from the hard shell of the backpack if it has one. Scuff up the shell a bit with sandpaper to get a better surface for the paint and mask the plastic edges of the backpack to protect the fabric. I used a plastic bag to cover the bottom of the backpack and taped the edges to keep any overspray from the fabric. Spray the backpack with white primer. Add coats as needed to completely cover the backpack graphic.
While the paint dries, mask out placement for the unicorn graphic before painting pink to get the best color saturation from the acrylic paints used for the cartoon graphics. Using a vinyl cutter, create a mask for the shape of the unicorn, rainbow, and Hello Unicorn lettering. I've included two files that you can download and use on a vinyl cutter - in Adobe Illustrator and Silhouette Studio formats. I did not mask out each individual stripe of the rainbow (I did by hand later), but if you'd like to add them you can edit the file before you cut.
The mask is actually three separate masks - the Hello Unicorn lettering, outline of the rainbow (note: it will need to be extended with masking tape to conform to the backpack's shape), and the unicorn. After cutting, peel away extra material and then transfer the mask to the backpack. Pieces of masking tape across the lettering will help keep them in place as you transfer check out this youtube video for the technique.
After the mask is in place, paint with a pink spray paint.
Step 2: Add Details With Acrylic Paint
Now it's time to paint the unicorn and rainbow details.
First, carefully peel away the mask over the rainbow, making sure to leave the lettering and unicorn shape in place. With a pencil, draw the lines of the rainbow stripes and carefully paint them in. I ended up using a combination of small brushes and masking tape to keep the edges crisp. This step took quite awhile, but is worth it for clean lines. Depending on your acrylic paint, you may need to build up a few layers.
After the rainbow is finished, use an Exacto knife to trace the edge of the unicorn graphic. I found that acrylic paint tends to pull and stretch, especially when using thicker layers, so scoring the edges will keep the vinyl from tugging on your paint and pulling it up.
Finish the painting by filling in the unicorn. I kept a printout of a screen capture from the show handy as a reference to work against as I painted. Take your time and sketch first with pencil then fill in the details with acrylics. I hand painted all the outlines with a small brush and black paint, but you could also use a paint marker for this step.
When all the painting is done, peel up the lettering to reveal the white primer underneath. I found this a lot easier than trying to paint white letters in over all the other layers. Make sure to trace the edges with a knife before removing to make sure no acrylic pulls up with the letters. Do any touch up painting as needed along edges.
Finally, add in the graffiti details with permanent marker and white paint. To add some extra realism, carefully dab a paper towel with some isopropyl alcohol over the marker to remove some of it and make it look worn. I also added some dirt detailing to rough it up a bit. When all the painting and detailing is complete, seal with an acrylic sealing spray and let set overnight.
Step 3: Create Channels for LED Strips
After the sealer has dried, open up the backpack. There are some flaps and pockets that you can cut out if you like.
Cut long strips of clear vinyl about 1.5" wide and stitch the top edge into the backpack, leaving the bottom edge open. This will create a channel to slide the LEDs into as an extra layer of protection. For the front hard shell, use glue to attach the vinyl. At the bottom hinge of the bag, leave a small opening in the vinyl to thread the LED strips and wires through.
Using some masking tape, trace the LED strip around the edges of each side the backpack to measure for fit. A full meter won't quite fit around the soft side of the backpack, so I ended up splicing about 4" of strip to the end to fill up the entire outline. This is optional, but makes for a better effect if you use the bag in any cosplay where you want to have it fully opened.
Note: it's best practice to test the strip before installing to catch any defects or damage. This is especially important if using random parts from your workspace rather than brand new product!
Step 4: Wire Up LED Strips
Identify the beginning of each LED strip by looking for a DIN or arrow pointing down the strip. Trim the connectors off of the strips, leaving ~1-2" of wire still connected to the strip and some on the connector. Set aside one of the female JST connectors and one of the male JST connectors. Take the LED strip you measured to fit for the hard shell side of the backpack and thread the wires through the opening in the vinyl to the soft side. Use some tape to hold the wires together to keep them from separating or catching on items in the pack.
Next, splice the two stripped ends of the LED strips together to a female connector, adding wire as necessary to give about 6-8" of space between the end of the strip and the connector. I also included a capacitor for extra protection from any power spikes. Use heatshrink on any exposed wires and to help bundle the wires together.
After all the wiring is done, push the strips up into the vinyl pockets around the edge of the pack and hot glue in place. If the LED strip overlaps the beginning of the strip too much, trim an LED or two from the strip to avoid any short circuits. Tuck the wire behind the LED strip on the fabric side of the backpack to hide it, paint pink if desired. Leave enough length of wire so that it does not get pulled too much when the backpack is open. Hot glue the edges of the vinyl over the LED strips to seal them and trim any excess vinyl away.
Step 5: Make a Pocket to Hold Electronics
From watching the show, it looks like the prop makers added a second zippered pouch in the backpack to hide the electronics and battery pack. Since I didn't feel like doing that much construction on the pack itself, I installed a matching pocket inside using some spare pink fabric I had. You can also use some of the trimmings from the pieces you cut away earlier.
Measure your pocket length to make sure it fits your battery pack in it. I used some cool vinyl I had and a fabric layer for my pocket, but it does not have to be lined. I also made two spaces in it - one for my wallet and phone and the other for the electronics to run the LEDs. On the pocket for the LEDs, attach velcro along two sides for easy access to plug and unplug the battery or get to the parts for repair. I also left an opening to thread the wiring through.
Glue or stitch the pocket to the inside of the pack and place the LED wiring inside of it.
Step 6: Install Reed Switch
To create the automatic light effect, we'll use a reed switch to sense when the backpack is open or closed. Measure two lengths of wire that are long enough to travel from the center top of the backpack along the sides of the pocket for the electronics, approximately 12-15 inches.
Solder one wire to each end of the reed switch and cover with head shrink. I used ribbon cable and split apart the ends to solder to the switch, which left a nice line of cabling that wouldn't get tangled on install.
Cut a small opening in the fabric of the backpack above the LED strip and a small hole on the other side toward the bottom seam. Be careful not to cut the LED strip. Slide the reed switch inside the gap and thread the wires down through the lower hole. Try to center the reed switch directly behind the LED strip so the magnet will trigger it.
Make sure you get a secure connection when gluing the reed switch in. Mine ended up sliding around inside the lining because I didn't put enough glue on it. As it moved away, the magnet stopped being close enough to trigger it. I opened up the seam again and repositioned with more glue to fix it.
After securing the reed switch, run the wiring down the side of the backpack to the velcro pocket you created and secure with thread or hot glue, leaving enough wire free to solder to the Pro Micro in the next step.
Step 7: Program Pro Micro and Solder Connections
Open up Arduino on your computer and plug in the Pro Micro. If you don't have support for the Pro Micro installed, check out the directions on SparkFun's Pro Micro Hookup Guide. You'll also need to install the Adafruit Neopixel Library through the Library Manager in the Sketch menu.
The program for this project is relatively simple, it will check the state of the reed switch and if triggered (when the magnet is near/backpack is closed) it will turn off the LED strips and if not triggered (magnet moves away/backpack is opened) it will turn them on.
Download the attached code and open the sketch in Arduino. You may need to adjust the number of LEDs depending on the density/size of the LED strips and base backpack used in your project. Don't worry if one strip is shorter than the other, use the higher of the two. Count the LEDs on the strip if you haven't already to get the correct number to use in your code.
When you are ready to upload code, open the Tools menu and select:
- Board: SparkFun Pro Micro
- Processor: ATmega32U4 (5V, 16 MHz)
Next, select the Port the Pro Micro is connected to. Then click upload. Unplug from your computer and power adapter before installing in your project.
After uploading the code, complete the hookup by soldering a male JST connecter that you set aside earlier and the reed switch to the Pro Micro as shown in the provided Fritzing diagram. Note that the colors in the diagram may differ from the LED strips you used, always double check the wiring on the LED strips to make sure DIN, VCC, and GND are all correctly placed. For example, my LED strips used red for VCC, yellow for GND, and green for DIN.
After soldering, test out the circuit by plugging the LED strips into the connector and holding a magnet near the reed switch. The LEDs should turn on when the magnet is moved away from the reed switch. The reed switch used in my project has around a 20mm activation zone.
Add some velcro inside the pocket and on the Pro Micro to keep it from moving around in your project.
Read more on how reed switches work in SparkFun's reed switch hookup guide.
Step 8: Install Magnet and Test
The final step is to install the magnet that will trigger the reed switch. Mark a place on the plastic of the rim of the hard shell side of the backpack above the LED strip. Tape the magnet in place and test to make sure it triggers the reed switch when closed before final install. Depending on the magnet it may need to be placed differently than in these photos. Carve away some of the plastic for a snug fit and glue the magnet in place. Paint if desired to further hide it.
Add any extra finishing details to the backpack like the black tactical webbing and any extra scuff marks. Fill with fake drugs in plastic baggies. You can use small saline bottles to be super accurate. Wax stick candy or mini glow sticks work great as a cheaper option.
Now your backpack is ready to bring to a con! I got a lot of great comments on this build at Denver Comic Con and many people asked where I bought it. I haven't seen any really good purchasable replicas of this backpack yet so it's a pretty special project for me. It even got a 'Wow!' from Dichen Lachman over on my Instagram :D. I hope you enjoy making one as much as I did!
Second Prize in the