Created March 1, 2020 © GPL3+

Smart IoT Tray

Make a smart IoT tray that keeps your food hot, can be turned on and off using a Kemet Proximity Sensor and can be remotely controlled.

IntermediateFull instructions provided10 hours65

Runner Ups

Make Sense of Our Proximity Sensor

Things used in this project

Hardware components

Adafruit Feather HUZZAH with ESP8266 WiFi

Resistor 10k ohm

Resistor 330 ohm

SparkFun Heating Pad

Breadboard (generic)

Power MOSFET N-Channel

Dadamachines Power Supply

SparkFun SHR Connector

Software apps and online services

Arduino IDE

Adafruit IO

Hand tools and fabrication machines

Soldering iron (generic)

Solder Wire, Lead Free

Shapeoko CNC

Story

Introduction

I wanted to make a smarter tray - one that had a dedicated place for drinks as well as having a space that would stay hot. I wanted to be able to control it remotely and I wanted a contactless way to trigger the hot mode on and off. Using the Kemet Proximity Sensor along with the Adafruit Feather Huzzah and Adafruit IO allowed me to accomplish my goal.

Kemet Proximity Sensor

Powering the kemet sensor with 5V seems to result in analog readings of 1024 consistently when my hand is over the sensor. I receive a string of high readings when I place my hand and then I receive another string of high readings when my hand moves from the sensor. Because of this, I waited until I had two pulses before I triggered the on/off function in my code. The sensor itself uses a SHR connector but functionally only uses three of the five pins. See the Things section for the exact connector. I followed the example that was provided in the tutorial of this contest but had to make some adjustments in order to get it to work.

Kemet Sensor

As you can see from the picture above, the colors from left to right are White, Purple, Green, Red, and Black respectively. From left to right for the sensor are Vin, Tx, Rx, Vout and Gnd respectively. This means for the device to be wired correctly, White should be connected to Vdd (5V in our case), Red should be connected to our analog input and black is connected to ground.

Building the Case

I wanted to make a nice looking enclosure that could have space for a couple of drinks as well as a relatively large space that could be heated with the heat pad. I needed to drill a hole for the proximity sensor as well as another hole when I wanted to give the user an easy indicator for when the device was on. I used my Shapeoko CNC to cut out the enclosure and a compound miter saw and a whole lot of sanding to get it just right. I decided to put some hairpin legs on it but it is not necessary whatsoever to have. I used a copper sheet and cut it to the hole size. The heat pad will warm up the copper and make the surface hot enough to maintain whatever the food's temperature is. I added a support underneath it because the copper is not strong enough to maintain the weight of even a small plate. See pictures below for the assembly.

1 / 12 • CNC simulation

Programming and Circuit Design

The circuit design can be found in the attachments and isn't anything too fancy. I used the Adafruit Feather Huzzah because it has WiFi on board and I had a spare one. You could use any ESP8266 module and probably have limited changes to what I did. The Kemet Vout does go to an analog in which I had to change after making the circuit design and I added a LED but both of those are pretty minor and the pins I used are in the code that I attached. See pictures below for my circuit design.

1 / 2

I'm trying to use the Adafruit IO platform more so I decided this would be a good project for it. I followed along with their tutorial for Digital In and Digital Out. You can find the instructions here. The design of the page was very basic with just a 0 and a 1 and a bar. Mixing both of the digital in and digital out examples allowed me to control the device locally and remotely. See the code attached for details.

Basic bar design

Proof of Concept

After assembling the device and programming it, you should be able to turn on the heat pad locally and remotely. If it works right, you should be able to do the same thing as in this video:

Schematics

Code

Main Program

#include "config.h"

#define LED_PIN 4

int Pyro = A0;
int heatpad = 14;
unsigned long PyroRead = 0;
unsigned long IR_threshold = 198000;
int anaValue = 0;
int pulses = 0;

// set up the 'digital' feed
AdafruitIO_Feed *digital = io.feed("digital");

// IR_threshold is in microsec (usec), therefore 198msec threshold
int LED = 7;
int Detected = LOW;
int IR_sensed = 0;

void setup() {
  
  pinMode (Pyro,INPUT); // IR Sensor connected to A1
  pinMode(heatpad, OUTPUT);
  pinMode(LED_PIN, OUTPUT);
  
  // start the serial connection
  Serial.begin(115200);

  // wait for serial monitor to open
  while(! Serial);

  // connect to io.adafruit.com
  Serial.print("Connecting to Adafruit IO");
  io.connect();

  // set up a message handler for the 'digital' feed.
  // the handleMessage function (defined below)
  // will be called whenever a message is
  // received from adafruit io.
  digital->onMessage(handleMessage);

  // wait for a connection
  while(io.status() < AIO_CONNECTED) {
    Serial.print(".");
    delay(500);
  }

  // we are connected
  Serial.println();
  Serial.println(io.statusText());
  digital->get();

}

void loop() {

  // io.run(); is required for all sketches.
  // it should always be present at the top of your loop
  // function. it keeps the client connected to
  // io.adafruit.com, and processes any incoming data.
  

  while ((IR_sensed < 2)){ //Break after 2 good triggers PyroRead = pulseIn(A1, HIGH); //Measure trigger point if(PyroRead > IR_threshold){ //Make sure trigger is over 198msec)
    while (pulses < 5) {
      io.run();
      anaValue = analogRead(Pyro);
      Serial.println(anaValue);
      if (anaValue == 1024) {
        pulses++;
      }
      else {
        pulses = 0;
      }
      delay(100);
    }

    IR_sensed++;
    pulses = 0;
    delay(100);
  }
  
  if (Detected == HIGH)
    {
      digitalWrite(heatpad, LOW);
      Detected = LOW;
      digitalWrite(4, LOW);
   }
  else {
    digitalWrite(heatpad, HIGH);
    Detected = HIGH;
    digitalWrite(4, HIGH);
  }

  digital->save(Detected);

  PyroRead = 0; // Reset readings
  IR_sensed = 0;
  delay(1000); // Accept triggers after a second
  
  

}

// this function is called whenever an 'digital' feed message
// is received from Adafruit IO. it was attached to
// the 'digital' feed in the setup() function above.
void handleMessage(AdafruitIO_Data *data) {

  Serial.print("received <- ");

  if(data->toPinLevel() == HIGH)
  {
    Serial.println("MANUAL HIGH");
    digitalWrite(heatpad, HIGH);
    Detected = HIGH;
    digitalWrite(4, HIGH);
    
  }
  else {
    Serial.println("MANUAL LOW");
    digitalWrite(heatpad, LOW);
    Detected = LOW;
    digitalWrite(4, LOW);
  }

  PyroRead = 0; // Reset readings
  IR_sensed = 0;

}

Credits

Alex Merchen

22 projects • 37 followers

I'm an EE with a Masters in ECE. I like building things.

Comments

Awards

Runner Ups

Make Sense of Our Proximity Sensor

Smart IoT Tray