This repository is for a smart clay timer project with arduino for the CASA0016 course. It uses a Feather Huzzah to measure temperature non-invasively using an infrared thermal camera and uses the change in temperature of clay as it dries as an indicator of progress of the drying process. This progress is displayed tangibly using a strip of RGB LEDs, much like a loading bar. With some calibration, this project may also be suitable for measuring the drying of other materials such as paint or as an automatic contactless thermometer.
PotteryProgress: The Smart Clay Timer/Sensor
Inital concept sketch. Note the differences in final LED colours used and the original position of the DHT22 sensor
The following hardware was used in this project:
- Adafruit Feather Huzzah (or similar ESP8266-based board)
- SR04 Ultrasonic distance sensor / range finder
- MLX90640 Infrared Thermal Camera (Pimoroni or similar with integrated surface-mount voltage regulation components)
- DHT22 temperature and humidity sensor
- Adafruit Neopixel stick (with 8 LEDs)
- Copper wires (sleeved) (in black, red, etc.)
- 3 10k Ohm resistors
- Proto/strip board
- Header pins male & female
The following dependencies must be installed for this project to work:
- ESP8266 board package to ensure the Arduino IDE can communicate and write code to the Feather Huzzah
- Adafruit MLX90640 library I found this simpler to use than the Sparkfun libraries and sketches suggested by Pimoroni
- Adafruit Neopixel library to control the Neopixels
- Math library for the round function to round floating point numbers to integers
- Adafruit DHT22 sensor library to interface and read from the DHT22 sensor
- ESP8266WifiMulti.h to connect to multiple WiFi networks
- ESP8266WebServer to use the ESP8266 as a web server capable of hosting simple webpages
The ultrasonic sensor and Neopixel LED strip require a 5V circuit to be powered, while the other sensors can work at 3.3V. The logic of the Feather Huzzah is 3.3V, hence it makes sense to maintain most of the load on the 3.3V circuit and provide a seperate circuit from the USB pin (5V) of the Huzzah to power the ultrasonic sensor and the LEDs. The disadvantage of taking such an approach with the Feather Huzzah is that a 5V power supply must be connected to the USB port to provide 5V to the USB output pin. This means that the device must be plugged into a 5V wall adapter or into a 5V power bank, which limits the settings in which it may be deployed. However, as this device is envisioned to be used within an indoor pottery studio setting, it is expected to be plugged into mains power most of the time.
For the various sensors, the following wiring was used:
- Ultrasonic sensor - pins 13 and 15 for the Echo (input, receiving the returning ultrasonic pulse) and Trigger (output, producing the ultrsonic pulse) pins respectively. 2 10k Ohm resistors are necessary to create a voltage divider to return a signal back to the Huzzah at 2.5V, within the logic level of the microcontroller
- DHT22 - pin 2 for the input. A 10k Ohm resistor is used as pull-up for this pin.
- Neopixel - pin 14 for the data_in (output signal from the ESP8266)
- MLX 90640 Thermal camera - the MLX90640 uses I2C to communicate with the ESP8266 (green wires) so connections to the Feather Huzzah should be straightforward as the SDA and SCL pins that make up the I2C connection are clearly labelled on the microcontroller's pinouts. Note that the illustration used here is for Adafruit's version of the MLX90640 board and therefore has some minor differences to Pimoroni's version. In particular, the Adafruit version has a 3V output pin which can be used to connect another load in series on the 3V circuit, whereas the Pimoroni version (used in this project) has an unused pin that serves no function.
Fritzing breadboard diagram
Fritzing circuit diagram
The Arduino built-in, DHT sensor and Adafruit MLX90640 libraries provide useful example sketches which may be used to test and understand the sensors. For the ultrasonic sensor, you can use the Ping sketch from the built-in examples to test and trouble shoot the sensor, and ensure that the pins that you have selected to produce and receive the ultrasonic pulse are behaving as expected.
For the DHT22 sensor, the DHT_Unified_Sensor exmple sketch provides a great overview of how to define and instantiate a DHT sensor object and then take regular readings from the sensor, which should be fairly straightfoward.
The MLX90640 thermal camera forms the heart of the device and this project and therefore is worth experimenting with in a bit further detail. Adafruit provide the MLX90640_simpletest example sketch, which provides a nice and simple way to test and visualise outputs from the camera. The script shows how to set up the camera to read infrared values and output these in the format of an array. These values are then visualised in the serial monitor using ascii characters:
Ascii character art from the infrared camera - a human hand is warm so it shows up very easily. Note that the camera is upside down inside the device!
By commenting out the #define PRINT_ASCIIART line and uncommenting the #define PRINT_TEMPERATURES line, it is also possible to get the raw temperature values output as floating point numbers rather than ascii characters.
Testing the device with a cold and moist object such as a glass of water straight from the tap
Calibrating this project to wet and dry clay required testing with a variety of objects to get a feel for how the temperatures of wet and dry objects might differ. Cold water in a glass was one such object and it was found that, the glass itself was almost always one or two degrees warmer than the water within it. More relevant to the project however, it was also found that bone-dry clay almost always had temperature readings around room temperature.
While getting an array of temperature readings from the camera is useful, what was really needed was a way of estimating the overall temperature of the object in front of the camera. Without getting bogged down in computer vision techniques, which aren't really ideal for the ESP8266 anyway, a simple way to approximate the temperature of the subject and ignore the background readings is simply to take the mode or most common temperature value in the frame. To ensure that the most common value is the correct one, the object must be placed reasonably close to the camera such that most of it fills the frame, which is where the ultrasonic sensor comes in. Using conditional statements, the Feather Huzzah only takes readings from the thermal camera whenever an object is placed within 15cm of the device's front face.
The solution to finding the mode per frame was to use a histogram type data structure (https://cplusplus.com/forum/general/257730/). This counts the frequency of each unique temperature value and stores them in key:value pairs, similar to a python dictionary.
histogram[T]++; //increment element(temperature reading) count
mode_count = std::max(mode_count, histogram[T]);
The key(s) with the highest count is/are therefore the mode(s), which can then be retrieved using a simple comparison statement in a for loop, the code for which was adapted from https://stackoverflow.com/questions/42194494/find-the-mode-of-an-unsorted-array-and-if-that-array-has-more-than-one-mode-or-n:
for (auto T: histogram){
if (T.second == mode_count) {
To ensure that there was a mode in the first place, which wouldn't exist if all the temperature values in the array were different from one another, the values were normalized by rounding them to the nearest integer.
The device can work without WiFi, however if you want to display data collected in a webpage served from the ESP8266 (see below section) you will need to set this up. The code has already been written into the startWiFi() function, all you need to do is set up up to two WiFi networks by entering their SSIDs and passwords into a file named arduino_secrets.h, which will be imported into the main code if you place it next to the main .ino file. If you wish to add more than two WiFi networks, you will need to modify the code slightly. After importing the ssid and password variable pairs for your additional networks into the main .ino file, you then need to call the wifiMulti.addAP() function once more for every additional WiFi network. Note that the code loops through the known WiFi networks you have assigned so if you assign a large list of WiFi networks, it may take some time to connect to the internet.
A PCB or maker strip board was considered essential to the project as the final device was envisioned to be quite small and compact as a potential consumer product. To achieve this, the mess of wires and the breadboard had to be miniaturised to fit into a relatively small enclosure. The most reasonable way to prototype this is to use a strip board, which has copper connections running in parallel strips along a board. New connections can be made by soldering wires from one strip to another and individual lengths of each strip can also be isolated by breaking the copper channel using a drill bit in a pin vise or another similar tool. In the image below for example, the pins on each side of the Feather Huzzah are isolated from each other using this technique:
The copper side of the strip board showing the pattern created by breaking the copper channels
The more expensive components, such as the Feather Huzzah and the MLX90640, were connected using male/female header pins so that they could be removed and reused, while components that had to be attached at specific positions below the front face of the enclosure were attached with breadboard connectors to allow some flexibility over their final placement.
The enclosure was based off a simple box design generated using the MakerCase website (https://en.makercase.com/#/)
The rear, side and bottom faces of the enclosure were to form a single piece, so these were glue together with Gorilla wood glue
The openings for the various sensors were measured and drawn into the .dxf file using Fusion360. The .dxf file was then used to lasercut 3mm plywood to make the box. Where errors were made, more precise measurements were taken with a pair of vernier calipers and used to correct the drawings.
Discarded plywood pieces of the enclosure with hand-written markings showing corrections to be made for the next cut
To secure the ultrasonic sensor and the Neopixel strip to the enclosure body, 2M screws and nuts were used. The SR04 has holes that are sufficiently tight that nuts will probably not be necessary to hold it securely if 2M screws are used.
The ESP8266 can be set up as a server to host a simple webpage (https://lastminuteengineers.com/esp8266-dht11-dht22-web-server-tutorial/).
The HTML code for the webpage can be found in the main arduino file itself:
String ptr = "<!DOCTYPE html> <html>\n";
ptr += "<head><meta name=\"viewport\" content=\"width=device-width, initial-scale=1.0, user-scalable=no\" >\n";
ptr += "<link href=\"https://fonts.googleapis.com/css?family=Silkscreen:400\" rel=\"stylesheet\">\n";
ptr += "<meta http-equiv=\"refresh\" content=\"10\" >\n";
ptr += "<title>Pottery Progress</title>\n";
ptr += "<style>html { font-family: Silkscreen; display: inline-block; margin: 0px auto; text-align center;}\n";
ptr += "body{margin-top: 50px;} h1 {color: #444444;margin: 50px auto 30px;}\n";
ptr += "p {font-size: 24px;color: #444444;margin-bottom: 10px;}\n";
ptr += "</style>\n";
ptr += "</head>\n";
ptr += "<body>\n";
ptr += "<div id=\"webpage\">\n";
ptr += "<h1>Pottery Progress</h1>\n";
ptr += "<img src=\"https://github.com/ethmacc/CASA0016_smart_clay_timer/blob/main/pot_drawing.png?raw=true\" width=\"300\">\n";
ptr += "<p>Air Temperature: ";
ptr += (int)AmbTemp;
ptr += " C</p>";
ptr += "<p>Humidity: ";
ptr += (int)Hum;
ptr += "%</p>";
ptr += "<p>Clay Temperature: ";
ptr += (int)ClayTemp;
ptr += " C</p>";
ptr += "<p>Your clay is ";
ptr += PercDry;
ptr += " % dry</p>";
ptr += "</div>\n";
ptr += "</body>\n";
ptr += "</html>\n";
The Google fonts website (https://fonts.google.com/) was linked into the HTML file to provide the Silkscreen font, which felt like it would work well visually with the robot face formed by the sensor ports in the front face of the enclosure. To provide some illustration and visual interest, a simple drawing of a pot, drawn from scratch, was also embedded in the webpage.
To view this webpage on another device (connected to the same WiFi network) you will need to enter the device IP address (printed in the serial monitor) into a web browser. The webpage will be visible at that address.
The Neopixel strip provides an ambient indicator of what is being sensed from the clay environment:
- Orange coloured LEDS indicate very dry air as read from the DHT22 (less than 20% Relative Humidity)
- Yellow coloured LEDs indicate moderately dry conditions (20 to 40% RH)
- Blue LEDs indicate humid conditions (greater than 40% RH)
The number of LEDs lit up out of the strip of 8 LEDs available indicates how dry the clay is. For example, if the sensors indicate the clay is most likely 50% dry, 4 out of 8 of the LEDs will be lit up.
- Simple LCD screen to show the thermal camera output in visual form, as well as display the device's IP address so that a user can browse to the webpage with the data output without needing to first connect the device to a computer to read the IP address off from the serial monitor
- Vibration motor/ buzzer, which could be used to indicate when the clay is done and dry.
- A dedicated PCB so that the device USB port can be placed at a more convenient location on its side.