Tinkercad
Basic Relay Setup
Cutting and Soldering
Plugging in the Wires
Basic Code
Blynk
Photocell
Photocell Code
Blynk Part 2
Enclosure

Published March 2, 2018 © LGPL

Lane Tech HS - PCL - <Lamp powered with Photocell and Relay>

This project controls the power going through an extension cord into a lamp using surrounding light.

IntermediateFull instructions provided10 hours1,120

Lane Tech HS - PCL - <Lamp powered with Photocell and Relay>

Things used in this project

Hardware components

Relay (generic)

Particle Photon

Extension Cord

Lamp

Resistor 10k ohm

SparkFun Photocell

Jumper wires (generic)

Male/Female Jumper Wires

Software apps and online services

Particle

Blynk

Hand tools and fabrication machines

Soldering iron (generic)

Exacto Knife

Wire Cutter

Story

This project was part of the Lane Tech HS Physical Computing Lab course. I created this project as part of the Home Automation / IoT project. To fit these requirements, I made a device that is turned on by a master control switch using the Blynk App, and that also turns the lamp on if it gets dark.

Tinkercad

The first thing I did was learn what the different ports of a relay are and what they mean (COM, NC, NO, VCC, GND, and IN). After this I created an online Tinkercad project using the relay they provided. It was a little different than the one I owned, but it helped me understand how relays worked.

1 / 2 • Wiring Diagram

Basic Relay Setup

The next step in the project was to hook up the actual relay I would be using. To do this I inserted positive wires into NO (Normally Open) and COM (Common), then I hooked these up to the LED as seen in the picture below. I connected IN (Input) to pin 11 on the Arduino (I used the Arduino because it doesn't require a wifi connection), I connected GND (Ground) to ground, and I connected VCC to 5v. All this did was turn the LED on. I connected the Arduino to my computer to power it.

Wiring of the Arduino.

Cutting and Soldering

The next step in the project was to essentially take apart the extension cord. To complete this project you have to cut through the positive side of your extension cord. On most new extension cords the positive side is smooth while the neutral side has grooves. If the two wires in your extension cord are the same, the larger prong is neutral and the smaller one is positive. After figuring out which side of your extension cord has power running through it, you want to cut only that wire in half, and then wire-strip (stripping away the protective casing to expose the wire) both sides. After cutting them in half you'll want to twist the wires as tight as you can and then pre-tin them completely. This means covering all of the exposed wire in solder.

Wire before soldering

Plugging in the Wires

The next step in the project is to connect the wire to relay. The half of the cord leading to the prongs is connected to NO and the other half is connected to COM. Make sure you're exposing as little wire as possible.

Basic Code

After this you once again connect IN to pin D6, connect GND to ground, and connect VCC to 3.3v, all on the Photon. Upload the code below and listen to your relay, if you have the same one I have you should be able to hear it clicking between closed and open. The Photon automatically sets output pins to LOW, so if you want your relay to be "off" when you start, make sure you set D6 to HIGH. Be careful with the relay, if you touch the bottom it will shock you.

1 / 4 • Code to make the relay turn on and off

When you are completely sure everything works, you can plug the extension cord connected to your relay into the wall, and plug in your lamp on the other side. Make sure your lamp is turned on. This part is the most dangerous part of the project so be extremely careful. Once you plug into your Photon, assuming you have not flashed any new code, it should turn your light on and off.

Blynk

The next step in the process is to connect your code to Blynk. To do this simply create an account on the Blynk app and create a new project. Make sure to email your authorization code to yourself, you'll need it to connect your Photon to the app. For our project we're going to create one button, and have it be digital button D6. Make sure the button is on switch mode. You will also need to download the Blynk library to your particle photon code. The following code will allow your Blynk app to turn your relay on and off.

Photocell

The next step in the project is to connect a photocell to your project. A photocell is pretty simple to set up. You want to connect one side of the photocell to A0 (Analog Pin 0). On that same side you'll want to connect it to aa resistor around 10kΩ and ground. The other side of your photocell should be connected to VIN

1 / 2

Photocell Code

After connecting your photocell, you'll want to read the voltage coming from it, and compare it to whatever the normal light in your room is (your Dark Threshold). If it is darker than your threshold the light turns on and vice versa. When this code is flashed, your light should turn on when you cover your photocell with your finger.

Blynk Part 2

The final step for setting up the hardware side of your project is making your Blynk button be a "master switch." This means nothing will work or turn on unless your button is switched on. To do this you'll need to change your button from digital D6 to Virtual V0, and flash the following code. The virtual pin allows you to read the value from your Blynk button.

1 / 2 • What your Blynk Button should look like

Enclosure

The final step in this project is to create an enclosure that can replicate turning the lights on and off, or plug in the project in your room. Since I had to present this in my classroom, I used a box that could become a "dark room" when the lid was closed. I used an exacto knife to cut two holes in the sides so that the two sides of the extension cord could slip through. Lastly, I taped down the breadboard and relay.

1 / 3 • The box with just the extension cord in it

And with that, you're done! Hope you enjoy your new device :)

Code

Project's code

// This #include statement was automatically added by the Particle IDE.
#include <blynk.h>
#define BLYNK_PRINT Serial
char auth[] = "YOUR_AUTH_CODE_HERE";

const float VCC = 4.98;
const float DARK_THRESHOLD = 1500; //If your photon reads less than this it should turn on.
const int LIGHT_PIN = A0;
float lightV;
int lightADC;
int pinValue;
 //NO -> LOW is on


void setup()
{
  Serial.begin(9600); //lets you check the voltage number
  pinMode(LIGHT_PIN, INPUT); //LIGHT_PIN is the photocell
  pinMode(D6, OUTPUT); //D6 is the relay
  digitalWrite(D6, HIGH); //D6 is automatically set to LOW, but this turns the relay on and we want the relay off at first.
  pinValue = 0; //Sets the VirtualPin to zero
  Blynk.begin(auth);
}

BLYNK_WRITE(V0) // V0 is the number of Virtual Pin  
{
    pinValue = param.asInt(); //This grabs the value of the virtual pin
}


void loop()
{
    Blynk.run();
    if(pinValue == 1 ) { //if the virtual pin is on
      lightADC = analogRead(LIGHT_PIN); //read the value the photocell is sending
      if (lightADC > 0)
      {
          
        lightV = (lightADC * VCC / 1023.0)*100; //Calculates voltage, then multiples by 100 to make the # easier to read
        Serial.println("Voltage: " + String(lightV) + " V"); //Displays Voltage
            if ((lightV) <= DARK_THRESHOLD) //If its dark
                digitalWrite(D6, LOW); //turn the relay and therefore the extension cord on
            else //if its not dark
                digitalWrite(D6, HIGH); //turn the relay and extension cord off
        Serial.println();
      }
    }
}

Credits

Lilly Moore

2 projects • 2 followers

Thanks to Ostin Jos.

Lane Tech HS - PCL - <Lamp powered with Photocell and Relay>