This is a felted knit bag that incorporates a temperature/humidity sensor connected to NeoPixels and a display module. The light display varies with changing temperatures and accurate data is shown on the LED display in both Fahrenheit and Celsius.
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Step 1: Materials Needed
Textiles (about $30-$50):
- 11 balls of felting wool
- #10 Knitting Needles
- Dark wool roving (optional for needle felt accents)
- Felting needles
- Fabric for the bag lining
- Zippers for the lining (to keep the electronics accessible)
- Thin foam (protection for the electronics)
Electronics ($130- $140):
- LilyPad ATmeg328 (Sparkfun) $19.95
- FTDI Cable
- DHT22 temperature-humidity sensor + extras (Adafruit Product ID: 385) $9.95
- 2x LilyPad LiPower (Sparkfun) $14.95
- 2x LiPo Batteries with charger (used here two 3.7V 4000mAh from ebay)
- 2x JST-PH Battery Extension Cable 500 mm (Adafruit Product ID: 1131) $1.95
- 3x NeoPixel Diffused 5mm Throug-Hole LED 5 pack (Adafruit Product ID: 1938) $4.95
- Monochrome 1.3" 128x64 OLED graphic display (Adafruit Product ID: 938) $ 24.50
- 2x Tactile Button Switches (Adafruit Product ID: 1685) $ 3.95 Note: The third wire is not really needed but the 2 wire switches were unavailable at the time
- Conductive thread (Adafruit Product ID:603) $4.50
- Various colors of Silicon Covered Stranded-Core Wire - 2m 30AWG (Adafruit Product ID: 2003) $0.75
Total Cost: $160-$190)
Cheaper alternatives are likely to be around. I did learn the hard way though that sometimes some of these cheaper things don't work too well...
- Soldering equipment
- Alligator clips
- Sewing Machine
Step 2: Knitting the Bag
This project takes 11 balls of Felt Virgin Wool Ecru from Ice Yarns and number 10 needles. The pattern is based on the Chambered Nautilus Tam pattern by Elizabeth Zimmerman (Book: Knit One Knit All) with the modification of 1 stitch every 20 rows after the first 60 rows. Word of caution - this made for a complex knit and is not recommended for novice knitters!
Reminder: For the two sides of the bags mirror images of the pattern need to be knitted. Again, not really for the beginner knitter...
Either stitch or crochet the two sides together and think about the shoulder strap or handle. For this bag I simply added a strap (15 stitches) knitted as a tube that will later get attached at the other end.
Obviously any shape or pattern would work for a bag like this. However, regardless of the shape or size of the bag, keep in mind that the felting process shrinks the project anywhere from 20-40%. It is highly recommended to knit/felt a swatch to better predict how much the final product will shrink.
Step 3: Felting the Bag
This is a rather large bag and thus easier to felt in the washing machine. It took about 20 minutes on the hot cycle and resulted in about 25% of shrinking. Careful monitoring during wet felting is recommended to avoid over-felting.
To accentuate the spiral design of the nautilus needle felting was used to add darker shading.
Tip: I was very impatient during this step and tried to needle felt before the bag was entirely dry - that cost me 5 felting needles! Once the bag is dry this step is MUCH easier so be patient.
Step 4: Preparing NeoPixels
These NeoPixels are not readily designed to be used in wearables. However, it is fairly easy to modify them so they can be sewn into projects. Use needle nose pliers to bend the prongs into small eyelets being careful to be keep track of the pins. To reduce confusion about which pin is which I marked them with sharpies (red for power and blue for ground - could not find my black sharpie...) and the data pins remained unmarked.
I found out later that this was still not sufficient as I accidentally flipped a few data pins causing some (much) pain later on getting them right. If I were to do this again I would definitely mark each of the four pins individually to avoid input/output pins.
Step 5: Sewing the NeoPixels
Using conductive thread all prepared NeoPixels are sewn into the bag. This is worked from the wrong side of the bag and the bulbs are pushed through the felted knit so they are visible from the front (this is where the knitting approach really made life easy as I could take advantage of small holes already present).
And yup, this is when I managed to get my wires crossed (literally) by inserting some of the NeoPixels backwards... Better preparation of the pins (see previous step) could have save a lot of aggravation here!
Both the power and the ground pins are sewn with a continuous thread each while the data pins (running in the center) are connecting the input pin of one NeoPixels with the output pin of the other. Pay attention to the orientation of the data pins so the input for the strand is closest to the main board.
Once the NeoPixels are in place it is time for the Lilipad and the power sources (see wiring diagram). At this point it is wise to work with alligator clips before committing to the hardware. Unlike more traditional electronics, undoing "sewn" circuits get very time consuming.
Step 6: Adding the Lilipad and Power
The final bag has two different power sources - one for the lights and the other for everything else. This was an adjustment that happened after finding out how power hungry the lights are (live and learn) and the pictures taken do not show the second power source until the end. Use the wiring diagram in the following step for clarification.
The Lilipad main board and the first Lipower are placed and sewn to the bag. Conductive thread is used to connect the two with each other and to hook the NeoPixels to pin # 6. Any connections where conductive thread was cut and/or knotted is sealed with hot glue to secure the connections.
Step 7: Wiring Diagram
The wires of the graphic display module appear to be twisted in this diagram. However, this is intentional because display module gets flipped when placed on the outside of the bag.
Step 8: Adding the Display Module and the Temperature Sensor
While it is fun to have different colored lights indicating ambient temperature ranges, a more accurate reading truly satisfies the inner (and outer) nerd and is needed to show humidity. The monochrome graphic display module not only allows for that but can also handle a few extras like snowflakes when things drop below freezing or any other monochrome animation...
The sensor and display module are first tested with a breadboard using the same power source as the Lilipad main board (the lights remain on their own circuit - LiPower/battery combo). See the previous wiring diagram for details.
Once everything works - something that will doubtlessly require multiple rounds of tinkering (a nice bottle of Merlot helps ease the pain and is highly recommended here) the hardware gets installed in the bag.
First cut a small (5x10 pin) piece of protoboard and solder the sensor and a 10K resistor in place. It was critical for this project to keep this component as small as possible so it would fit in the center of the spiral of the Nautilus. Solder silicon wires to the power, ground and data pins and feed the wires from the front of the bag to the back. In similar fashion the display module is soldered to silicon wires and installed in the bag (wires are pushed to the back before stitching the module down.
The silicon wires that are attached to the sensor and display module are soldered to the appropriate pins on the Lilipad and LiPower (a little cardboard beneath the main board is sufficient to protect the textiles from the heat of the solder).
Use the wiring diagram as a reference since the pictures are a little much!
Step 9: Finishing Touches on Electronics
In order to avoid stress on the connections and accidental pulling of the wires as the bag is in use, everything is hand stitched and fastened to the bag.
Note: Neither the sensor nor the display module are visible in the first picture because they are placed on the outside of the bag.
Also, I added a little bit more dark roving around the display module and carefully needle felted that in place to clean up the aesthetics.
Step 10: Programming
Please note that an interesting bug occurred. The sensor only works properly after the FTDI cable is unplugged and the bag is powered independently.
Step 11: Inside of the Bag
The lining of the bag serves the purpose of practically and internal organization as well as the protection of the wiring and electronic components.
It is important to remember that all components need to remain accessible after the lining is installed (large zipper does the trick). This makes it easy to reprogram the bag and trouble shoot issues as they no doubt will arise through the use of the bag.
The lining also contains a pocket for the batteries which are connected to their respective LiPower sources via battery extension which makes battery removal for recharging much easier.
Step 12: Adding the Switches
An added benefit with the two battery approach is that the two circuits can be operated independently. This means that the main board, sensor and written display can stay all the time, but the lights can worked independently depending on power availability or circumstances.
In addition, it would be very awkward to access the electronic panel on the inside of the bag each time to use the slide switch on the LiPowers and I wanted to make this as accessible as possible.
I spliced the tactile switches into the JST extension cables so I could feed the switches into the the strap of the bag and easily operate them. This means that the LiPowers stay on all the time and power is controlled through the switches easily accessible.
Again keeping with the theme of ease-of-use I placed the battery pouch right on the inside of the bag so that I do not have to go into the "guts" (between bag and lining where all the electronic components are). The JST extension cables reach out into that pouch and removing batteries to recharge them is as simple as taking out my cell phone.
Step 13: Finishing
Before sewing in the lining, a small piece of foam is placed over the electronics and held in place with a few stitches. The fully finished lining is then hand-stitched into the bag and voila - the bag is ready to be used and without a doubt start many a conversations.