Everyone has had that moment where they are too impatient and just have to take that first bite of pizza fresh out of the oven only to have it burn the roof of their mouth with the heat of a thousand suns. I know I have had these moments and I finally decided to make something to help prevent it. Using an Arduino and a temperature sensor, a homemade spatula is created to serve the pizza and measure the temperature of the sauce and topping of the pizza.

To achieve this, I gave my design some basic requirements:

The wiring (without the Arduino) should be built into the spatula
The user should be notified if it is too hot, or if it is the right temperature to eat
The spatula should be washable and food safe

In this Instructable, I will show you the circuit design, code, and the final spatula assembly along with a demo video.

Step 1: Tools and Supplies

Tools:

Drill (only if you need to modify the spatula like I did)
Drill Bits
Food Safe Adhesive (ASI #502 Silicone, for example)

Supplies:

(1) 4.7kOhm Resistor
(2) 220Ohm Resistor
(1) Green LED
(1) Red LED
(1) Arduino (Any variety will work, I will use a Seeeduino) w/associated data cord for computer connection
(1) Jumper Wires
(1) Spatula
(1) DS18B20 Temperature Sensor (Prebuilt is preferred, I use one encapsulated in stainless steel for food safety and easy cleaning)
(1) Breadboard

Optional Items:

Digital Multi-meter (for troubleshooting the circuit)
Soldering Iron and Solder (For more permanent circuitry)

Step 2: Software and Libraries

To use the microcontroller and the DS18B20 Temperature Sensor you will need to download and install some software and an Arduino Library

Arduino IDE: This is where the code will be written and compiled

Find this here: https://www.arduino.cc/en/Main/Software

2. OneWire Library

Find this here: https://github.com/RobTillaart/Arduino/tree/master...

You can also find this library and install it within the Arduino IDE by going to the tools tab and manage libraries where you can search "OneWire"

Step 3: Build the Circuit

See the schematic attached as a guide for building the circuitry. Connect the LED's to the proper micro-controller IO as shown on the schematic. Connect the sensor output to IO2 on the micro-controller.

Step 4: Modifying the Spatula

This step is crucial in the creation of the final design. Depending on the spatula you have, you can modify it in many different ways. The main part of this modification is cutting out a hole where the temperature sensor can sit. I started by tracing the sensor on the top of the flat part of the spatula. Then I drilled out the whole using a drill. Next, I drilled a hole for the wire of the sensor to go through. This is more cosmetic than functional. Next, I drilled two holes for the LED's to sit in. At this point, I only made further modifications to hide the wires, so this can be done according to whatever spatula you have.

Step 5: Uploading and Modifying the Code

The code is based off of a library that can be found within the Arduino IDE. Once the OneWire library is downloaded and installed as described in Step 2, an example for the DS18B20 can be found in the IDE under File --> Examples. I modified the 'DS18B20_Simple' example to work with LED's. The code is attached here, once the library is downloaded and installed, the code can be downloaded and run in the Arduino IDE. In the code, the temperature in the if statement can be adjusted to your tastes.

DS18B20_Instructable.ino
Download

Step 6: Wire-up the Spatula

The components are placed into the holes drilled in the previous step. To keep the wires clean looking and to avoid any unplugging or short circuits, I wrapped any loose wires in electrical tape. Now, the wires lead to a breadboard where the resistors are at and the spatula components meetup with the micro-controller. This is where the jumper cables are good for quick connections. Be sure to double check the wiring before you plug the micro-controller into your laptop. The last picture shows me testing the LED's to make sure the wiring was correct. In the next step, the code is discussed.

Step 7: Final Result

The Video here shows the spatula at work on a fresh out of the oven pizza. The green LED turns off and the red LED turns on after a little while. This take at least 15-20 seconds to level out when the spatula is left sitting at room temperature. I chose the temperature here to be 60 degrees Celsius or 160 degrees Fahrenheit. Thus, when the LED turns green, the pizza is at a temperature that will no burn the roof of your mouth.