Introduction: Not Yet Cookie Jar


I am a nanny and I love watching and interacting with children! There are different things to learn and different ways to teach when interacting with kids. My girls are great but they have a sweet tooth. So obviously I have a problem with the little girls getting into their cookie jar without having permission. I wanted to apply what I have learned about craft technologies to a real world application with my kids and this idea came to be. I used a 8MHz Gemma, a rechargeable battery, conductive string, a light sensor and 7 neo-pixels. The lights are dark when the lid is closed and the lights flare up and alert me when the lid is lifted!

Where to buy:

Gemma: or

Neo Pixels:

Conductive String:


Step 1: Sew Your Neo Pixels to Felt or Paper

I chose to use felt to sew my neo pixels to with the conductive thread. I lined them all up and made sure to attach the correct ends to the correct ends. (I urge you to double check because even with thinking I was right, I had to unstitch one out that was backwards.) I used a parallel circuit and lined them up. All of the input pins or arrow symbols need to be attached but only one at a time by the string, and then tied off individually. IT IS VERY IMPORTANT to not let extra threads or knot strings overlap, on the front side or the back side. I had one pixel that seemed to be malfunctioning until I realized my strings were hanging off and touching other threads or parts of the pixel.

Step 2: Secure the Gemma to the Felt and Attach to the Neo Pixels

Attach the gemma to the felt using non conductive thread and then sew the appropriate lines to the neo pixels. Attach the negative node to the negative side (-) of the parallel circuit. Make sure to keep the stitches small and tight so that they don't fray and also tighter stitches are more conductive. Attach the D1 node to the arrow nodes on the neo pixel (->). Lastly, attach the Vout node to the positive side of the neo pixels (+). Be aware of frayed wires and hanging strings off knots. Also make sure to line up your diagram before hand so that no strings are forced to cross each other in the stitching.

Step 3: Attach the Light Sensor to the Felt and Sew It to the Gemma

The method of attachment is the same as the step before hand, but attaching the light sensor. Sew in the light sensor and attach the negative (-) node to the GRN node, the S node to the D2 node and the positive (+) node to the 3Vo Node. Make sure the sensor is far enough away to allow for your specific designs. The light sensor needs to be able to read the light when exposed.

Step 4: Cut Out the Pixels and Gemma and Light Sensor to Fit Over Your Design

Once you have everything secured you can reduce the amount of felt used and cut it out. I even made a little pocket for the battery. Make sure that you use non conductive string to not short any circuits.


See how my tin is made out of metal? Yeah that messes up my stitches because it conducts and shorts when it touches the metal. I fixed this by putting tape on the back, and felt on the front. It makes it a little thicker but avoids the shorts.

Step 6: Code

My code is fairly simple, it is dark when there is no light and turns on when there is light. I changed the color values to make it more fun for my kiddos! I had to adjust the number of neo pixels and the delay is not very long, so immediate fun and reaction.

Step 7: It Turns on and Off

See in the pictures how the light is on and then off with just a small shadow!?

Step 8: Finale! Add to the Jar or Tin

The felt can be laid over the lip of the jar and when the lid is on the lights are off. I attached mine to the jar with hot glue, but its able to be removed and put on another jar. This is a great tool for dieting (for adults), play and reinforcement for children. Enjoy!!